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www.laser focusworld.com Ju ly 2010
Scanning optics slice 3D images PAGE 48
Structured fiber advances short-pulse lasers PAGE 52
Imaging spectrometers get smaller PAGE 57
Manufacturers’ Product Showcase PAGE 71
Femtosecond amplifi er output gets a boost PAGE 39
International Resource for Technology and Applications in the Global Photonics Industry
Microplasma displays are fl exible and transparent PAGE 33
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The Tunability You Want.The Power and Control You Need.
www.newfocus.com©2010 Newport Corporation
Put the power of New Focus™ into your BEC experiment and gain the power, control
and ease-of-use you desire. The combination of our New Focus Vortex™ II or Velocity®
laser with our new VAMP™ tapered amplifi er delivers more power and precision,
tunability and control than ever before. The result is an unsurpassed BEC solution
with clean solid tuning from a single seed laser, fi ber coupled input option, and WIFI
connectivity for ease-of-use along with:
• 100 GHz or 8000 GHz of mode hop free tuning
• Narrow line-width unaltered after amplifi cation
• >1 watt tunable light
• Center Wavelength from 760 nm to 980 nm
In addition, New Focus is part of the Newport family of brands allowing for the
seamless integration of optical components and vibration control products from a
single source. With over 40 years of expertise and innovation New Focus and Newport
deliver innovative solutions and the global resources and services you need.
Find out more by calling (408) 980 4370. You may also visit us at
www.newport.com/newfocusBEC for more information.
VAMP test data
Amplified Mode Hop Free Tuning from 765 nm to 782 nm
765 770 775 780
Wavelength (nm)
0
2
4
6
8
10
12
14
16
18
20
Inpu
t Pow
er (m
W)
P(out)P(in)
Outp
ut P
ower
Fro
m A
mpl
ifier
(W) 1.0
0.5
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___________________________
JULY 2010 ■ VOL . 46, NO. 7
International Resource for Technology and Applicationsin the Global Photonics Industry
July 2010 www.laserfocusworld.com Laser Focus World 2
d e p a r t m e n t sc o l u m n s
n e w s b r e a k s w o r l d n e w s
L A S E R S ■ O P T I C S ■ D E T E C T O R S ■ I M A G I N G ■ F I B E R O P T I C S ■ I N S T R U M E N T A T I O N
13 Diode-Pumped Solid-State Lasers Modelocked Ti:sapphire
laser is pumped by blue laser diodes.
14 Metamaterials Electromagnetic ‘black hole’
is experimentally realized
16 Infrared Imaging OLED converts IR to visible:
Night vision for your cell phone?
18 Microstructured Fiber Fiber-sensor technology
is thin-skinned but robust
22 Photodetectors LWIR plasmonic detector has breakthrough
sensitivity and quantum effi ciency
24 Dye Lasers Small pulsed organic laser is highly effi cient
9
Resonant metalens resolves to λ/80
LC-fi lled PC fi bers form tunable
bandpass fi lter
Wake Forest patents low-cost, highly
effi cient plastic-optical-fi ber solar cells
10
Cold-atom gravimeter requires
only one laser beam
11
Biological protein can self-assemble into tiny
nanolasers and other photonic devices
Optical gain seen in plasmonic waveguides
7 THE EDITOR’S DESK
Material matters
Stephen G. Anderson
Associate Publisher/Chief Editor
31 BUSINESS FORUM
How can I develop my consulting business?
Milton Chang
76 IN MY VIEW
The sayings of Rear Admiral Grace Murray Hopper, USN
Jeffrey Bairstow
66 NEW PRODUCTS
71 MANUFACTURERS’ PRODUCT SHOWCASE
74 BUSINESS RESOURCE CENTER
75 ADVERTISING/WEB INDEX
75 SALES OFFICES
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3Laser Focus World www.laserfocusworld.com July 2010
f e a t u r e s
LFW on the Web Visit www.laserfocusworld.com for breaking news and Web-exclusive articles
33 COVER STORY
By successfully confi n-
ing plasmas in arrays of
microcavities, research-
ers and engineers at the
U. of Illinois have real-
ized thin, inexpensive
light-emitting sheets.
Shown is a fl exible and
transparent display
based on microplasmas
sealed within two thin
plastic sheets. (Image
courtesy of the Univer-
sity of Illinois and Eden
Park Illumination)
33 FLEXIBLE DISPLAYS
Sheetlike microplasma arrays have many applications
By shrinking plasmas to microscopic
dimensions, thin light-emitting sheets
ideally suited for displays, specialty
and general illumination, environmental
remediation, and sterilization have
become a reality.
J. Gary Eden and Sung-Jin Park
39 ULTRAFAST LASERS
Femtosecond amplifi er output gets a boost
Advanced ultrafast amplifi ers combine
high power, excellent beam quality,
and high repetition rates in a turnkey
system without cryogenic cooling.
Steve Butcher and Marco Arrigoni
48 SCANNING OPTICS
Optical-sectioning microscope uses a single-pixel detector
A programmable-array microscope
relies on a digital-micromirror device
and a sampling technique called
compressive sensing to take 2D slices
of 3D objects, all the while collecting
light with just a single detector.
John Wallace
51 FIBERS FOR FIBER LASERS
Structured fi ber advances short-pulse laser performance
Chirally coupled core fi ber enables
scaling of single-mode fi ber core size—
essential for the high-peak-power laser
operation needed in high-precision
materials processing applications.
Phill Amaya
57 MINIATURIZED IMAGING
SPECTROMETERS
Prism-based spectrometers tackle today’s miniaturization requirements
Because a prism transmits 90% of
light over an extended wavelength
range, matching it to a CCD detector
with close to 90% quantum effi ciency
creates a nearly ideal system that, with
some tradeoffs, can be miniaturized
to meet portable spectroscopy
application needs. Jeremy Lerner
61 PHOTONIC FRONTIERS:
FREQUENCY-SHIFTED
DIODE LASERS
Shifting semiconductor laser wavelengths poses challenges
Nonlinear optics can generate new
lines from semiconductor lasers by
harmonic generation and frequency
mixing, but it requires high power, good
beam quality, and narrow linewidth.
Jeff Hecht
Coming
in August
Ellipsometry characterizes thin-fi lms in the IR
Modern IR-surface ellipsometry instruments and associated data analysis software can provide accurate and repeatable thickness and optical property measurements of substrates, as well as single and multilayer fi lm samples, over a large spectral range. In this article, authors at J.A. Woollam Co. and LohnStar Optics use several real-life examples to demonstrate the versatility of ellipsometers for characterization of substrates and thin-fi lms.
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5Laser Focus World www.laserfocusworld.com July 2010
laserfocusworld.online More Features, News & Products
e x c l u s i v e f e a t u r e s e x t r a s
®
www.laserfocusworld.compowering photonics technologies & applications on
Blog: Inside the world of venture capital
Done it vs. Read about it I was having a drink with an old friend who is the best product marketing guy I know, he was also my BoD member and
an excellent operating partner at Accel. We were discussing the diffi culty in hiring the right VP Sales, VP Marketing, and, hardest of
all, VP Product Management.
http://bit.ly/
bcMr4v
Blog: Opto Insider
Time for customers to pony up There was news recently that Morgenthaler Ventures is ending its track for funding opto hardware start-up companies, mostly in silicon, but including optical components. This is not good news, to be sure, but maybe it’s time again for the systems integrators to fi nally pony up for components research.http://bit.
ly/9AWUuX
Videos
CLEO/Laser Focus World
Innovation AwardsLearn more about the technologies that make this year’s Innovation Awards winner
and honorable mentions stand out from the crowd.http://bit.ly/
cWedVu
UV DETECTORS
Zinc-oxide materials and their alloys redefi ne UV sensingZinc oxide (ZnO) and its alloy MgZnO are emerging as promising ultraviolet-sensing candidates due to their direct wide bandgap (wider than aluminum gallium nitride) and the ability to tailor their electronic, magnetic, and optical properties through doping and alloying. Shiva Hullavarad and Nilima Hullavarad
http://bit.ly/9bsLOk
PRODUCT FOCUS: OPTICAL SPECTRUM ANALYZERS
Understanding the latest features in optical spectrum analyzersAn OSA has long been an important tool for signal discrimination in
networking. New capabilities such as in-band OSNR and wider dynamic range are expanding their potential in next-gen networks and extending them to other applications. Valerie C. Coffey
http://bit.ly/91hRxU
CLEO 2010 Rocks!The 2010 CLEO Conference on Lasers and Electro-Optics (CLEO) celebrated the 50th Anniversary of the Laser with special displays, events, plenary and technical sessions, and an outstanding LasersRock! celebration.http://bit.ly/9waAL6
Visit our web siteFind in-depth news and features, as well as photonics products at our newly redesigned web site featuring topic centers on biophotonics, instrumentation, imaging and detectors, and more.www.laserfocusworld.com
Post your video! Send file to: [email protected]
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______
_______
_____
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_______________________
___________________
editor’s desk
Christine A. Shaw Senior Vice President & Group Publisher,
(603) 891-9178; [email protected]
Stephen G. Anderson Assoc. Publisher/Editor in Chief, (603) 891-9320; [email protected]
Gail Overton Senior Editor, (603) 305-4756; [email protected]
John Wallace Senior Editor, (603) 891-9228; [email protected]
Carrie Meadows Managing Editor, (603) 891-9382; [email protected]
Sharon A. MacLeod Executive Assistant, (603) 891-9224; [email protected]
CONTRIBUTING EDITORS
Jeffrey Bairstow In My View, [email protected]
David A. Belforte Industrial Lasers, (508) 347-9324; [email protected]
Valerie Coffey (978) 263-4485; [email protected]
Jeff Hecht Photonic Frontiers, (617) 965-3834; [email protected]
Conard Holton Imaging, (603) 891-9161; [email protected]
D. Jason Palmer Europe, 44 (0)7960 363 308; [email protected]
Adrienne Adler Marketing Manager
Suzanne Heiser Art Director
Sheila Ward Production Manager
Chris Hipp Senior Illustrator
Diane Giannini Web Publisher
Debbie Bouley Audience Development Manager
Steve Archer Ad Services Manager
EDITORIAL OFFICES
Laser Focus World
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98 Spit Brook Road, LL-1, Nashua, NH 03062-5737
(603) 891-0123; fax (603) 891-0574
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CORPORATE OFFICERS
Frank T. Lauinger Chairman
Robert F. Biolchini President and CEO
Mark Wilmoth Chief Financial Offi cer
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Gloria S. Adams Senior Vice President,
Audience Development and Book Publishing
Subscription inquiries
(847) 559-7520; fax (847) 291-4816
e-mail: [email protected]
web: www.lfw-subscribe.com
EDITORIAL ADVISORY BOARD
Dan Botez, University of Wisconsin-
Madison; Connie Chang-
Hasnain, UC Berkeley Center for
Opto-electronic Nanostructured
Semiconductor Technologies;
Pat Edsell, Avanex;
Jason Eichenholz, Ocean Optics;
Thomas Giallorenzi, Naval
Research Laboratory;
Ron Gibbs, Ron Gibbs Associates;
Anthony M. Johnson, Center
for Advanced Studies in Photonics
Research, University of Maryland
Baltimore County;
Kenneth Kaufmann, Hamamatsu
Corp.; Larry Marshall, Southern
Cross Venture Partners; Jan Melles,
Photonics Investments;
Masahiro Joe Nagasawa, TEM Co.
Ltd.; David Richardson, University
of Southampton; Ralph A. Rotolante,Vicon Infrared; Toby Strite, JDS
Uniphase.
7Laser Focus World www.laserfocusworld.com July 2010
Stephen G. Anderson
Associate Publisher/
Editor in Chief
Material mattersThe fi eld of materials processing has come a long way from the early days of blasting holes in stacks of
steel razor blades with CO2 lasers. Its advance has required research and development into both the
interaction of light with the materials involved and the design of the lasers themselves. For a light/mate-
rial interaction to be routinely successful, the laser must deliver its output at a specifi c wavelength, pow-
er, beam quality, and stability. Interest in the use of short pulses for high-precision materials processing
applications like direct structuring of components or microvia hole drilling has “raised the bar” on such
performance specifi cations, especially pulse length and repetition rates. Because of their effi ciency and
relative simplicity, fi ber lasers are particularly attractive for industrial materials processing and recent
developments in structured fi bers may help broaden their use in short-pulse applications (see page 51).
The use of short (or fast) pulses in basic science is well established, though the pulses typical in the re-
search arena are much shorter than those generally used for materials processing. But while the order of
magnitude of the pulsewidth may be different, the desire for power and beam quality coupled with pulse-
to-pulse stability and higher repetition rates is common to both markets. Ultrafast amplifi ers are one route
to higher-power femtosecond pulses, though they have traditionally been a complex option—at least one
system now offers a performance boost from a turnkey package without cryogenic cooling (see page 39).
Working with materials in a different context has led to many exciting advances in photonics, one of
which is highlighted on our cover. The emerging fi eld of microplasma
technology could lead to some novel displays and lighting. The exam-
ple shown is a fl exible and transparent display based on an array of
microplasmas sealed between two plastic sheets (see also page 33).
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9Laser Focus World www.laserfocusworld.com July 2010
newsbreaks
Resonant metalens resolves to λ/80
Researchers at the Institut Langevin, ESPCI ParisTech & CNRS
(Paris, France) have designed and created a novel form of sub-
wavelength-structured lens called a metalens, which breaks the
diffraction limit but operates in a way very different from that of
a conventional near-fi eld lens. The experimental prototype, built
for use in the microwave region (as are many fi rst attempts at
fabricating metamaterial optics), produced a far-fi eld image at a
resolution of λ/80 of an object consisting of 16 point sources.
The metalens consists of a 2D array of identical
subwavelength-sized resonators (in the prototype, they are
copper wires); the object, which is placed in the near fi eld of the
metalens, is illuminated with broadband light. The near-fi eld
energy captured by the lens decomposes into many different
spatial modes, each of which remains in the resonators for a
different length of time, with the modes with highest spatial
detail remaining the longest. The far-fi eld output is recorded
and the image reconstructed using an inversion algorithm. The
researchers plan to further increase resolution by adding some
disorder to the resonators to enhance dispersion. They believe
that metalenses can be created at visible wavelengths using
nanoparticles or nanowires as resonators. Contact Geoffroy
Lerosey at [email protected].
LC-fi lled PC fi bers form
tunable bandpass fi lter
Two short sections of optical fi ber that combine
to become an electrically tunable bandpass fi lter
have been fabricated by scientists at the Technical
University of Denmark (Lyngby, Denmark) and NKT
Photonics (Birkerød, Denmark). The 10 mm long
sections are each large-mode-area solid-core
photonic-crystal (PC) fi bers with their holes fi lled
with a fl uid of liquid-crystal (LC) molecules; the
hole diameters and the LC type are different for
each section. The two sections are placed serially
and butt-coupled in a silicon v-groove containing
gold electrodes along the sides of the groove; two
single-mode fi bers are also held in the ends of the
groove and butt-coupled to the sections to couple
light in and out of the PC-fi ber arrangement.
Light from a supercontinuum-fi ber source is
coupled into the device. One LC type is a long-
pass fi lter and the other a shortpass fi lter; the
combination produces a bandpass fi lter trans-
mitting over the 1520 to 1680 nm range. When
a driving voltage variable between 90 and 120 V
is applied to one LC and no voltage to the other,
the shortpass edge of the fi lter can be tuned
over a 36 nm bandwidth, with the longpass
edge immobile. A similar process applied con-
versely to the fi ber sections produces a longpass
tuning range of 12 nm with no shortpass change.
Contact Lei Wei at [email protected].
Wake Forest patents low-cost, highly
effi cient plastic-optical-fi ber solar cells
A new type of potentially low-cost solar cell that is twice as effi cient as tra-
ditional organic solar cells—and may even rival silicon fl at-panel cells—has
been patented by research professors in the Center for Nanotechnology and
Molecular Materials at Wake Forest University (Winston-Salem, NC). Fiber-
Cell, a Winston-Salem spinoff of the nanotechnology center, has already li-
censed the technology for commercialization and has successfully fabricated
lightweight and fl exible solar-cell modules using inexpensive roll-to-roll and
spray-on techniques.
The solar cell is made
using millions of tiny
plastic optical fi bers
that collect light at
oblique angles, prolong-
ing the effi cient collec-
tion of sunlight from
early morning through
evening hours. The fi ber
structure is composed
of polymethylmethacry-
late or perfl uorocyclobu-
tyl aligned optical fi bers followed by an interior indium tin oxide (ITO)-based
transparent conductor layer and a polythiophene:butyric acid methyl ester ab-
sorptive cladding layer. An aluminum external refl ector and contact along the
outside of the fi bers funnels incoming light down the fi ber, where photons
are absorbed by the cladding layer and converted to electrons. Prototype 10
× 10 cm solar panels have been fabricated and are now undergoing testing at
other laboratories. Contact David Carroll at [email protected].
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π/2
π
π/2
Interferometerduring free fall
3D pyramidalmagneto-optic trap
Raman 1
Raman2
Coils
Detection
newsbreaks
NEWS ONLINESee more breaking news at
www.laserfocusworld.com
Cold-atom gravimeter requires only one laser beamAtom interferometers used as sensitive gravimeters (which de-
tect the strength of the local gravity fi eld, or g) are normally
quite complex, requiring nine independent laser beams and
associated optics, making them too cumbersome to use in the
fi eld. Researchers at LYN-SYRTE, UPMC (Paris, France) have
created a cold-atom gravimeter based on Raman transitions
that requires only one laser beam and is very compact. The
device relies on a 3D hollow pyramidal magneto-optic trap
(MOT) to trap the atoms; the four inner mirrors of the trap
also produce the proper polarizations to drive the Raman tran-
sitions and measure the positions of the falling atoms.
The MOT, which is custom-made from two glass corner
cubes and two glass isosceles rectangular prisms, has a 20 × 20
mm pyramid base and mirror faces that are perpendicular to
each other to within one arc minute. Two laser diodes are tuned
to frequencies close enough to correspond to the microwave
transition of the ground levels of rubidium (Rb). The combined
collimated beam enters along the axis along which the Rb at-
oms fall. Measurement of g is achieved by adjusting the Raman
frequency difference until its chirp compensates the measured
Doppler shift (which changes as the atoms fall). Measurements
taken over a 50 h span matched variations expected from the
earth’s tides, with a short-term (1 s) sensitivity of 1.7 × 10-7 g.
Contact Arnaud Landragin at [email protected].
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Laser Focus World
newsbreaks
Optical gain seen
in plasmonic
waveguides
Propagation of surface-plasmon polaritons
(SPPs) with optical gain over macroscopic
distances has been demonstrated in a collbo-
ration by the University of Iceland (Reykjavik,
Iceland), Harvard Medical School (Boston, MA),
the University of Cologne (Cologne, Germany),
and the Fraunhofer Institute for Applied Optics
and Precision Engineering (Jena, Germany).
To overcome the substantial ohmic losses
normally seen at the plasmon-dielectric inter-
face, the researchers fabricated symmetric di-
electric-metal-dielectric waveguides support-
ing coupled SPP modes on the top and bottom
interfaces of a metal fi lm. Because mode con-
fi nement and propagation loss for these long-
range SPP modes decreases with metal thick-
ness, amplifi ed spontaneous emission (ASE)
for the propagating SPPs can be observed.
The waveguides consisted of a 4 nm thick
gold layer and a 1 μm layer of a fl uorescent
poly(phenylene vinylene) derivative blended
with a large-bandgap poly(spirofl uorene) poly-
mer and an alkyl compound that were sand-
wiched between two 20 μm thick transparent
polymer layers on a silicon substrate. Experi-
ments that gradually increased 532 nm pump
power to the waveguide produced ASE near
600 nm. The measured net optical gain was
8 cm-1, which corresponds to a 3000-fold sig-
nal increase after 1 cm of propagation. Con-
tact Malte C. Gather at [email protected].
Biological protein can self-assemble into tiny nanolasers and other photonic devices
Found in the cells of nearly every living thing,
the protein clathrin forms into tripod-shaped
subunits called triskelia that sort and transport
chemicals into cells by folding around them.
While multiple triskelia can self-assemble into
cage structures with 20 to 100 nm diameters for
applications in drug delivery and disease target-
ing, scientists at ExQor Technologies (Boston,
MA) see a host of other nanoscale electronic
and photonic applications for clathrin that could
rival those for silicon or other inorganic devices,
including a bio-nanolaser as small as 25 nm.
A spherical scaffold of clathrin subunits forms
ExQor’s patented clathrin bio-nanolaser. How
can a chromophore so small (25 to 50 nm in size)
serve as a cavity for visible light? ExQor says it
forces chromophore-microcavity interaction, and
this combination possesses a high-enough Q for
lasing. In this way, the bio-nanolaser produces
self-generated power in a sub-100-nm diameter
structure for potential applications in illuminating
and identifying (or possibly destroying) particular
biological tissues by functionalizing the structure
with antibodies or other agents that can target
particular pathogens or even certain cells. In ad-
dition, ExQor says quantum-mechanical effects
could be used that might enable unique, spin-
based, self-assembling nanoelectronic/nano-
photonic devices and even bio-based quantum
computers composed of clathrin protein. Contact
Franco Vitaliano at [email protected].
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Improving the quality of light
Visit our website to request your copy: http://optosigma.com/Contact/litrequest.asp
Visit our website to request your copy: http://optosigma.com/Contact/litrequest.asp
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HR, ROC =100 mm
Ti:Al2O3crystal
Fused silicaprisms Slit Output
TocHR,ROC = 75 mm
HR: High reflector ROC: Radius of curvature SBR: Saturable Bragg reflector
HR/SBR
GaN diode laser
1 W, 452 nm
world newsTechnical advances from around the globe
Got News? Please send articles to [email protected]
13Laser Focus World www.laserfocusworld.com July 2010
plasmonic
detector
See page 22
Although titanium-doped sapphire is a versatile laser gain ma-
terial and the main ingredient in widely tunable and ultrafast
Ti:sapphire lasers used across a broad spectrum of photonic ap-
plications, it requires a high-brightness (bulky and expensive)
pump source—typically, a multiwatt argon-ion or frequency-
doubled neodymium laser. Now, increased power levels for gal-
lium nitride (GaN)-based blue and green laser diodes have en-
abled researchers at the University of Strathclyde’s Institute of
Photonics (Glasgow, Scotland) to be the fi rst to demonstrate a
modelocked Ti:sapphire laser directly pumped by a laser diode.1
An unlikely result
Because the optical power of blue and green laser diodes is gen-
erally low and their wavelength is poorly matched to the broad,
but weak absorption spectrum of the Ti:sapphire gain material,
the laser industry has always felt that diode-pumped Ti:sapphire
was an unlikely achievement. Nonetheless, a compact 1 W, 452
nm GaN laser diode from Nichia (Tokushima, Japan) is suffi cient
for a Ti:sapphire laser with a continuous-wave output of 19 mW
at 800 nm in a standard cavity (see fi gure).
To achieve lasing, an aspherical collimating lens, a two-el-
ement cylindrical-lens telescope, and a spherical focusing
lens were used to concentrate the laser-diode output onto a
Ti:sapphire crystal within a four-mirror cavity. The calculated
cavity-waist radius was 25 × 15 μm in the crystal. For an output
coupling of 0.5%, a modelocking threshold of 750 mW and a
maximum average output power of 9 mW were obtained with
870 mW incident on the crystal. Using interferometric autocor-
relation, the transform-limited output had a measured full-width
half-maximum pulsewidth of 116 fs.
Challenges remain
The measured output power was lower than predicted by mod-
eling. The researchers say this is due to pump-induced losses at
the lasing wavelength; however, the losses are not observed at
wavelengths above 477 nm. Because progress has been made in
longer-wavelength GaN laser diodes, the team is confi dent that
future experiments will soon produce a higher-output-power di-
rect-diode-pumped Ti:sapphire laser. Even using the current laser
diode at 452 nm along with double-sided pumping or polariza-
tion-combining techniques, the research team is confi dent that
output powers around 50 mW could be achieved.
“Diode-laser-pumping of Ti:sapphire enables drastic reductions
in complexity over current systems,” says PhD student Peter
Roth. “As a result, some of the unrivaled performance of today’s
high-cost tabletop Ti:sapphire lasers may soon be available at a
fraction of the current cost and footprint. With currently avail-
able GaN diode lasers [approximately 1 W per device around
450 nm], a tunable femtosecond Ti:sapphire laser with an aver-
age output power of roughly 50 mW should be possible by mul-
tiplexing two diodes... Such a laser would fi nd numerous applica-
tions from imaging to spectroscopy—for example, as a bolt-on
accessory to a fl uorescence microscope.” —Gail Overton
REFERENCE
1. P.W. Roth et al., “Modelocking of a diode-laser-pumped Ti:sapphire la-
ser,” CLEO 2010, paper CMNN1, San Jose, CA.
Commercially available blue laser diodes from Nichia (top right) are
used in a compact setup (lower diagram) for the fi rst time as a low-
cost pump source for a Ti:sapphire laser in place of conventional
bulky and higher-cost frequency doubled solid-state lasers (top left).
(Courtesy of the University of Strathclyde)
Modelocked Ti:sapphire laser is pumped by blue laser diodes
D I O D E - P U M P E D S O L I D - S T A T E L A S E R S
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world news
Electromagnetic ‘black hole’ is experimentally realizedThe subwavelength structure of optical
metamaterials gives them their unique
properties—and also makes them chal-
lenging to fabricate. This is why meta-
materials researchers sometimes fi rst
opt to put their ideas into practice in the
microwave region, which brings the size
of a structure’s unit cell up from a few
hundred nanometers to a few millime-
ters. Once proven with microwaves, the
concept can then (at least sometimes) be
scaled down into the optical regime.
Researchers at Southeast University
(Nanjing, China) have taken an idea fi rst
proposed last year and implemented it in
the microwave region.1 The idea—a meta-
material omnidirectional optical absorb-
er, or electromagnetic “black hole”—was
fi rst proposed last year; if ultimately cre-
ated in the optical region, the device could
be useful for maximizing the light absorp-
tion of solar cells and photodetectors.2
Radially varying
permittivity
The experimental mi-
crowave device is 2D for
simplicity (see Fig. 1). Its
overall effect is that of
a dielectric cylinder with
a lossy inner core and a
lossless circular shell with
a permittivity that varies with radius. All
electromagnetic waves of any polariza-
tion at the design frequency that hit the
cylinder, even at a glancing angle, are
captured and spiral inward to the core.
As in many microwave metamaterial
structures, the unit cells consist of piec-
es of circuit-board material with specifi c
metal shapes etched onto them. To create
a radially varying permittivity, the metal
shapes are changed as a function of radius.
For example, the shapes could be circular
rings, “I” shapes, or Jerusalem crosses; the
dimensions of the individual shapes can
be varied as well. The researchers chose a
non-resonant I shape for the outer shell of
the absorber, and an electric-fi eld-coupled
(ELC) resonator for the inner core.
A microwave frequency of 18 GHz was
chosen for the experiments. The unit cells
were 1.8 mm in size, or about 1/10 the
M E T A M A T E R I A L S
FIGURE 1. A 2D metamaterial omnidirectional absorber of
microwave radiation, or “black hole,” is made of concentric dielectric
sheets containing different metal patterns, one type for the core
and another for the outer shell. (Courtesy of Southeast University)
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________________
LightMachinery www.lightmachinery.com
Pulsed CO2 LasersLightMachinery pulsed CO2
lasers have a very low cost of
operation and are built for a wide
variety of applications in precision
manufacturing and R&D.
Micro-machining, wire stripping,
ultrasonics, plasma generation,
marking, date coding, anti-
counterfeit, pulsed laser deposition
Ultra-reliable lasers andresponsive customer servce
15Laser Focus World www.laserfocusworld.com July 2010
wavelength of the radiation to be cap-
tured; the entire device had 60 concen-
tric layers, with all layers three cells high.
To fi x the layers in place, circular slots
were cut into a styrofoam board and the
layers fi t into the slots.
Dark shadows
In the experiment, a nearfi eld scanning
system measured the incident micro-
waves and what happened to them as
they entered the absorber; the scanning
system could measure a 400 mm2 area
to a resolution of 0.5 mm (the absorb-
er itself was 216 mm in diameter). For
comparison, specialized numerical soft-
ware was used to simulate the absorber
and its ability to capture microwaves.
The absorption of a simulated Gauss-
ian beam striking the absorber at nor-
mal and off-center incidences was cal-
culated to be 99.94% and 98.72%,
respectively. Experimentally, it is diffi -
cult to create a small Gaussian micro-
wave beam, so an easier-to-generate
beam was used for the experiment. The
path and behavior of the beam, which
was narrow but slightly divergent, was
mapped and shown to be similar in be-
havior to simulations; in both, the beam
is seen to enter the absorber and spiral
toward the core.
Additional simulations of the response
of the absorber to a plane wave were
made for the distributions of both the
electric fi eld and the power (see Fig. 2). A
simulation of the behavior of the absorber
when subjected to an electric fi eld radi-
ated by a nearby monopole source agreed
well with the experimental measurements
of the same arrangement; both showed a
shadow region cast by the absorber.
The researchers believe that, because
the core of the device absorbs radiation
and emits it as heat, the omnidirection-
al absorber could fi nd use as a thermal
emitter or a “harvester” of electromag-
netic radiation.—John Wallace
REFERENCES
1. Q. Cheng et al., New J. Phys. 12, 063006
(2010).
2. E.E. Narimanova and A.V. Kildishev, Appl.
Phys. Lett. 95, 041106 (2009).
FIGURE 2. In a simulation, the absorber
responds to a plane wave, modifying
the electric fi eld (top) and blocking the
power (second image). A simulation of the
absorber and a nearby point source (third
image) matches well with experimental
measurements (bottom). (Courtesy of
Southeast University)
100 200 300
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world news
July 2010 www.laserfocusworld.com Laser Focus World 16
OLED converts IR to visible: Night vision for your cell phone?Optical upconversion—the process
of converting light at one wavelength
to that of a shorter wavelength (with
“up” being higher in the frequency
spectrum)—is possible by directly
combining photodetectors with LEDs.
Unfortunately, the fabrication process
is diffi cult for inorganic or even hybrid
organic/inorganic devices and photon-
to-photon conversion effi ciencies are
very low—typically less than 1%. In
addition, fabrication is expensive, and
some alternative upconversion methods
using quantum dots as an infrared (IR)
absorber suffer from high dark currents.
But thanks to advances in organic pho-
todetectors and organic LEDs (OLEDs)
with very high external quantum ef-
fi ciencies (EQEs) on the order of 20%,
researchers at the University of Florida
(Gainesville, FL) have demonstrated a
more effi cient all-organic upconversion
device that just may make night vision
on your cell phone a possibility.1
All organic
The organic upconversion device, fab-
ricated on an indium tin oxide (ITO)
substrate with overall dimensions of
I N F R A R E D I M A G I N G
In the absence of 830 nm IR radiation (left), a 0.04 cm2 all-organic upconversion device
remains dark. But in the presence of 830 nm illumination, the all-organic device upconverts
this radiation to visible green light (right). (Courtesy of the University of Florida)
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_______
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��������� ��������������������������������������
�
Consider us your partner in ultrafast laser research��������������� ����������������� � ��������� ! ���������" ���#$���%�������� ���������! &���� "�'����!������������(��%��" !! ���) �&��*
�������������������� �������������������� ���������������������������������������������������������������������������������������������������
world news
July 2010 www.laserfocusworld.com Laser Focus World 18
0.04 cm2, consisted of a tin phthalo-
cyanine (SnPc)-based bulk heterostruc-
ture layer as a near-IR (NIR) sensitizer
and an iridium-doped biphenyl OLED
layer as a phosphorescent emitter—
one of the most effi cient OLED materi-
als in use today. In photovoltaic mode,
the EQE of the NIR sensitizer layer can
be higher than 20%, while the EQE for
the OLED emitter layer is close to 20%
(compared to typical EQE values of less
than 5% for most conventional fl uores-
cent OLEDs).
In the absence of IR radiation, the
poor-hole-transport NIR sensitizer keeps
the OLED layer in the off state. But
upon photoexcitation, photogenerated
holes are injected into the OLED layer
and recombine with electrons injected
from a cathode layer to emit visible light.
The 100 nm thick NIR sensitizer layer
or fi lm has strong NIR absorption up to
1000 nm, with a peak at 740 nm. Using
an 830 nm, 14.1 mW/cm2 NIR source,
green light emission began at 2.7 V and
reached a luminance of 853 cd/m2 at
15 V. At 12.7 V, the on/off ratio of lu-
minescence intensity was about 1400
(see fi gure).
Even though maximum photon-to-
photon conversion effi ciency was only
2.7% for this device, the researchers
say that this value represents an or-
der-of-magnitude increase compared
to conventional (and more expensive
and complicated) hybrid organic/inor-
ganic devices. “Since OLEDs are be-
ing used for fl at-panel displays, the
costs of making these organic devices
are expected to be low because they
can use the existing OLED manufac-
turing infrastructure,” says Franky So,
associate professor of materials sci-
ence and engineering at the Universi-
ty of Florida.—Gail Overton
REFERENCE
1. D.Y. Kim et al., Adv. Mat. 22, 1–4 (2010).
Fiber-sensor technology is thin-skinned but robustProgress continues apace for a European
project aiming to create a fully integrated
photonic sensing “skin” that can be used
anywhere that requires close monitor-
ing of mechanical properties. The three-
year European Commission-funded proj-
ect, known as “photonic skins for optical
sensing” (PHOSFOS), has now perfected
its fi ber-production methods and has its
sights set largely on medical applications.
The 2.5-million-Euro PHOSFOS project is
being led by Francis Berghmans of the Free
University Brussels in Belgium, in collabora-
tion with a number of European universities
and the nanotechnology fi rm IMEC (Leu-
ven, Belgium). At the project’s heart is the
M ICROST RUCT U R ED F I BER
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_______________________
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____________________
Protect YOUR High Power Protect YOUR High Power Laser from BackLaser from Back--ReflectionsReflections
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!����� �� "#$$%!����� �� "#$$% &���� ����� &���� ����� '������'������ ������� ��������� �� &������� ��������� �� &(( �������� &����)� %*+ �� ������ ��� �� ���� ��� ��������&����)� %*+ �� ������ ��� �� ���� ��� ��������
%������ ��� ��� ���� ����� ��� �����, ����� ��� �� %������ ��� ��� ���� ����� ��� �����, ����� ��� �� ��������--���� ���, ��� �� � ������, ������� �� ������ ���� ���, ��� �� � ������, ������� �� ������ ������� ��� ���� ��������� ������� ��� ���� ���������
Electro-OpticsTechnology, Inc.www.eotech.com/[email protected]
inc.800-697-6782
world news
July 2010 www.laserfocusworld.com Laser Focus World 20
use of fi ber Bragg gratings created in silica
fi bers, microstructured fi bers, or exotic
plastic optical fi bers. Those in turn are to be
embedded in a thin foil or skin which the
team envisions could be put to uses rang-
ing from dentistry to civil engineering.
Key to the whole enterprise, Berghmans
says, is the integration of the elements—
the ability to integrate the optical sensing
functionality with on-board signal pro-
cessing, a power source, and even wireless
communication inside the fl exible poly-
mer skin. The skin can then be tacked to,
wrapped around, or built into any shape
the application requires.
“There are other ways to do it but not
in such an integrated manner,” he says.
“You’re getting your complete system
inside a fl exible material that can be at-
tached to anything you would like. It’s ap-
plicable in many different cases, whether
you’re thinking of medical applications or
of structural health monitoring—since ev-
erything is embedded and comes in a sin-
gle system, you’re not limited.”
The idea for PHOSFOS came from a
longstanding collaboration. “We were
working with microstructured fi bers and
had collaborations with the University
of Ghent and IMEC,” Berghmans says.
“They had the microsystems technology,
thinning diodes down until they were fl ex-
ible. We said it would be great if we could
combine everything to achieve these fully
fl edged integrated sensor systems.”
A PHOSFOS photonic-crystal fi ber (shown
here as a preform) will be patterned with
Bragg gratings and be embedded in a
fl exible polymer skin for sensing (top). An
experimental polymer skin, illuminated
with a supercontinuum source, is wrapped
around a surface to be monitored (bottom).
(Courtesy of Vrije Universiteit Brussel)
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Time (s)
Tem
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ture
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0 10 20 30 40 50 60
25
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35
40
/ Expected servo response
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Slope gain 4.47 s
Servo performance
Calculating optimum servo constants
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21Laser Focus World www.laserfocusworld.com July 2010
Insensitive to temperature
But making fi ber Bragg gratings in a num-
ber of types of fi bers while maintaining
optical performance wasn’t—and still
isn’t—a straightforward business. One
principal problem was limiting the tem-
perature sensitivity of the photonic skins;
they should measure the same mechanical
properties regardless of the ambient tem-
perature. Berghmans is somewhat guard-
ed about the secret but says that the team
now has fi bers with a temperature sensi-
tivity so low as to be unmeasurable.
“You have to take advantage of the
thermal properties of the polymer fi ber;
normally these things are quite sensitive
to temperature, but if you thermally treat
them in a proper way, you can achieve
writing multiplex gratings.”
Most recently, the team pulled off a
landmark result: fi ber Bragg gratings with
features smaller than ever before, made
point by point with an ultrafast near-IR
laser.1 Each period of the grating is made
with a single pulse, and the grating is built
up by translating the fi ber through the fo-
cused spot. The team’s method is simple—
their optical setup doesn’t even attempt to
account for the curvature of the fi ber, for
instance—so it bodes well for large-scale
manufacturing in the future.
For now, the team is working to make
the production of the fi bers reliable and
repeatable. The European-funded part of
the project fi nishes early next year and
potential uses for the skins are already
mounting up.
“The killer applications are defi nitely
in the medical fi eld,” Berghmans notes.
“We’re now working toward a demon-
strator for respiratory monitoring, and
there’s another project in artifi cial limbs
or ‘smart prosthetics.’”—Jason Palmer
REFERENCE
1. T. Geernaert et al., Opt. Lett. 35, p. 1647 (2010).
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July 2010 www.laserfocusworld.com Laser Focus World 22
world news
LWIR plasmonic detector has breakthrough sensitivity and quantum effi ciency
Building on earlier work, researchers in
the Bio-inspired Sensors and Optoelec-
tronics Laboratory (BISOL) at Northwest-
ern University (Evanston, IL) have devel-
oped a long-wavelength infrared (LWIR)
photodetector.1
The performance of this quantum-well
IR photodetector (QWIP) was enhanced
by applying surface plasmons via peri-
odic holes fabricated in a gold-foil layer
above the quantum-well structure. For
electromagnetic waves normal to the
quantum-well surface, a properly de-
signed plasmonic array forms standing
waves with a long propagation length,
producing a cavity effect that leads to
an enhanced transverse plasmonic mode
that resonates with electron intersub-
band transitions in the quantum well and
excites additional carriers to generate a
strong photocurrent.
Designing the plasmonic array
Because photodetection is only en-
hanced if the wave-generating surface
plasmons are perpendicular to the sur-
face (due to the intersubband-polariza-
tion selection rule), 3D fi nite-difference
time-domain modeling was used to op-
timize the surface-plasmon waves and
electric-fi eld distribution. By optimizing
the surface-normal component of the
electric-fi eld intensity distribution at 8
μm (the desired operation wavelength
of the LWIR detector), the parameters
of the plasmonic array could be deter-
mined. Holes with 1.4 μm diameter in
a lattice with a 2.9 μm lattice constant
were fabricated in a 40 nm thick gold-
fi lm layer using focused ion beam (FIB)
milling over the semiconductor structure
(see fi gure). This gold layer could also be
fabricated over large areas using super-
lens lithography.2
The quantum-well structure was de-
signed to achieve a peak absorption
wavelength of 8 μm with a bound-to-
continuum transition. The indium phos-
phide/indium gallium arsenide (InP/In-
GaAs) structure includes eight periods
of 5.6 nm thick In0.53Ga0.47As doped
with a 2.5 × 1017/cm3 silicon (Si) con-
centration and 50 nm thick undoped
InP quantum barriers. These quantum
wells are sandwiched between two
highly doped (1018 Si concentration)
In0.53Ga0.47As layers 40 nm thick at the
top and 500 nm thick at the bottom
that form ohmic contacts. The thinner
top layer insures maximum proximity of
the quantum-well structure to the gold
plasmonic layer fabricated on its surface.
P H O T O D E T E C T O R S
Finite-difference time-domain modeling was used to design a gold plasmonic layer (left) that
enhances photoconductivity of a long-wavelength QWIP. Scanning-electron microscopy
shows the actual plasmonic layer as a series of holes fabricated in a gold layer (right).
(Courtesy of Northwestern University)
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world news
July 2010 www.laserfocusworld.com Laser Focus World 24
Enhanced sensitivity
Analysis of the enhancement ratio of the
electromagnetic fi eld for a QWIP struc-
ture with and without the plasmonic layer
shows that this layer enhances the fi eld
by a factor of fi ve. Peak responsivity of
the device occurs at approximately 8.06
μm and is as high as 7 A/W for IR light
at normal incidence to the detector sur-
face. Because of the strong plasmonic en-
hancement of the electric fi eld, the mea-
sured peak detectivity of approximately
7.4 × 1010 cm Hz1/2/W is a few times
higher than for other InP/In0.53Ga0.47As
devices operating at a similar wavelength
and temperature. In addition, the full-
width half-maximum (FWHM) of the ab-
sorption spectrum is approximately 0.84
μm, almost half that of identical quan-
tum-well-only structures without the
plasmonic layer.
The researchers surmise that this nar-
row spectral response is due to strong
modulation of the QWIP structure by
the surface-plasmon resonance of the
gold array holes. While a narrow spec-
trum is favorable to applications that
require high spectral resolution, it is less
favorable for broadband detection.
Northwestern University associ-
ate professor Hooman Mohseni says,
“Our plasmonic layer is a perfect match
for QWIP, since it addresses the main
drawbacks of this technology. Not only
does it address the low quantum ef-
fi ciency of QWIP by enhancing the
fi eld intensity, but it also eliminates the
natural insensitivity of a QWIP to the
normal incident light.” Lead author Wei
Wu adds, “Interestingly, our plasmonic
design also performs as an antirefl ec-
tive coating, and we have plans to cre-
ate new devices over a broader spectral
range.”—Gail Overton
REFERENCES
1 . W. Wu et al., Appl. Phys. Lett. 96, 161107
(May 2010).
2. W. Wu et al., Nanotech. 18, 485302 (2007).
Small pulsed organic laser is highly effi cient
An organic optically pumped solid-state
laser called a vertical external-cavity sur-
face-emitting organic laser (VECSOL), de-
veloped by scientists at the Laboratoire
de Physique des Lasers at Université Paris
(Villetaneuse, France), produces a high-
quality beam at a conversion effi ciency
of 43%, and also is tunable.1 With further
development, the dye laser could be of
practical use for sensing or communica-
tions over plastic optical fi bers.
The gain medium is an organic poly-
methyl methacrylate (PMMA) fi lm doped
with Rhodamine 640 to 1% by weight
and spun-cast onto a fl at mirror to a
thickness of a few microns. The fl at mirror
has a refl ectivity greater than 99.5% for
D Y E L A S E R S
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___________
1 μm & 1.5 μm
for � a l l
1�μm�&�1.5�μm�
Fiber�Lasers
CW�&�pulsed�units,�optical�tweezers,�
For�complete�list�of�lasers�and�laser
RPMC�Lasers�Inc��203��Joseph�St��O
For�more�information�contract�[email protected]
p p
amplifiers/EDFAs,��polarized,�and�
custom�units.�
� you r � l a se r � needs…
Laser Diodesase odes620nm�to�2.3μmMultimode�or�Single�mode
s�diodes,�See�www.rpmclasers.com
O’Fallon�MO�63366���636�272�7227
For�more�information�contract�[email protected]
world news
July 2010 www.laserfocusworld.com Laser Focus World 26
wavelengths between 600 and 660 nm;
a concave (200 mm radius of curvature)
output-coupler mirror with a refl ectiv-
ity of 98% between 600 and 880 mm is
placed 4 mm away from the fl at mirror to
complete the laser cavity.
The two mirrors are transparent to light
at 532 nm, which is the pump wave-
length. The PMMA fi lm, however, ab-
sorbs 80% of the pump light in a single
pass when cast at a 17 μm thickness. The
VECSOL is pumped by a frequency-dou-
bled Nd:YAG laser beam emitting either a
“long pulse” of 7 ns duration, or a “short
pulse” of 0.5 ns duration, both with a 10
Hz repetition rate and a pump-beam di-
ameter of 140 μm (see fi gure).
Serendipitous tunability
For long-pulse pumping, the VECSOL
shows a lasing threshold of 1.8 μJ, a maxi-
mum output energy of 6 μJ (870 W peak
power), and an optical-to-optical effi ciency
of 43% (a quantum effi ciency of 63%). The
emission, which is linearly polarized in the
direction of the pump beam and is diffrac-
tion-limited (beam quality M2 of 1.0), is cen-
tered at a wavelength of about 655 nm but
consists of several peaks between 640 and
670 nm spaced by 7.5 μm—which is the
free spectral range of the Fabry-Perot etalon
formed by the thickness of the PMMA fi lm.
A VECSOL with a plano-concave resonator is pumped at 523 nm and emits at around 650
nm with a conversion effi ciency of 43%. (Courtesy of S. Forget, Laboratoire de Physique des
Lasers, CNRS/Université Paris 13)
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___________
©2010 Newport Corporation
Newport. The Brands of Innovation.
NewportRotation Stages
NewportAgilis™ Optical Mounts
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Spectra-PhysicsIndustrial & Ultrafast Lasers
OrielLight Sources
OrielMonochromators
Richardson GratingsDiffraction Gratings
NewportOptical Tables
NewportMotion Controllers
At Newport our mission is to continuously evolve our knowledge and
experience in order to deliver innovative products and solutions that advance
our customer’s technologies. To deliver upon our mission, we feel it is vital
to possess expertise and experience across a broad spectrum of technologies and
interconnected products.
For over 40 years, Newport has continued to grow and today is built upon world-class
brands such as Corion®, New Focus™, Oriel® Instruments, Richardson Gratings™ and
Spectra-Physics®. Alone, each of these brands has a rich history of product innovation
and expertise. Together, we provide a synergy of knowledge across a broad spectrum
of products along with the ability to deliver unsurpassed solutions and integration.
We are dedicated to maintaining the high quality and integrity of each of these
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Today, Newport is one company comprised of industry leading brands, stronger
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40 years of support, and we look forward to many more years of partnership.
Visit our website at www.Newport.com/brands-5 or call for more specifi c information
at 800-222-6440.
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As a result of the spin-casting, the PMMA fi lm ended up with a vari-
ation in thickness across the mirror; this allows the laser to be tuned
over a 20 nm range by laterally translating the mirror.
The researchers also tested PMMA thicknesses of 10, 5.6,
and 2.35 μm. They observed the expected variation in peak
spacing for the different thicknesses; the spacing for the thin-
nest fi lm was large enough that the laser produced only a single
peak (although the single peak was not tunable because the
thinnest coating had a uniform thickness).
Short-pulse pumping produced a threshold of 0.95 μJ, a max-
imum output energy of 0.7 μJ (2 kW peak power), and a con-
version effi ciency of 6.3%.
The researchers note that the cavity length for the VECSOL
can be increased to 60 mm for long-pulse pumping and 10 mm
for short-pulse pumping, allowing experimenters to insert intra-
cavity optics.
“This laser could be interesting for applications which require
a cheap, compact, easy-to-handle tunable source in the visible
range,” says Sebastien Chénais, one of the researchers. “The
key difference between the VECSOL and distributed-feedback
organic lasers or organic microcavity lasers is the perfect diffrac-
tion-limited beam quality and the very high conversion effi cien-
cies that are attainable. The beam can for instance be coupled
easily to a polymer optical fi ber, whose transmission is maxi-
mum around 650 nm, which corresponds to the wavelength
range of our laser. This could then be used for short-haul data
communications. Another potential application is spectroscopy
of organic molecules, including biological systems, or chemical
sensing. It could then replace expensive and bulky optical para-
metric oscillators or liquid dye lasers in those fi elds where mod-
est energies in a pulsed mode are required.”
Chénais believes that, provided some improvements are
made to the VECSOL (for example, adding well-controlled
wavelength tunability), it could be of interest to industry. The
cost of the whole system is now approximately the cost of the
pump laser, he notes; with a cheaper pump source such as a
laser diode, the device can become cost-effective.
Easily recoated
“The ultimate goal would be the achievement of electrical pumping
with an organic semiconductor as the gain medium, but this per-
spective is today still a big challenge for the community and cannot
be regarded as realistic within a short-term period,” says Chénais.
“The limitation brought about by the inherent low photostability of
organic dyes is highly reduced compared to solid-state dye lasers
using bulk dye-doped polymer blocks (or compared to other more
complex structures that require a patterning of the active medium),
since here it takes only a few minutes to rinse the mirror and coat it
with a fresh active layer.”—John Wallace
REFERENCE
1. H. Rabbani-Haghhighi et al., Opt. Lett. 35, 12, p. 1968 (2010).
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High-volume manufacturing, rapid engineering development, andworldwide service and support make Coherent the leading supplierof diode laser products to system builders in pumping, materialsprocessing, defense, medical and printing applications.
From epitaxial growth to device packaging and system assembly,vertically integrated manufacturing gives us control of every processand product parameter. You’re guaranteed consistently superiorperformance and reliability in device after device, batch after batch,year after year – as well as lower ownership costs.
To learn more about partnering with the most capable and responsive diode laser manufacturer in the world, visit our website at www.Coherent.com/diodes/preferred or call 1-800-527-3786.
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Offering Standard Products and Custom Solutions.
Coherent – The Preferred Diode Laser Supplier.
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31Laser Focus World www.laserfocusworld.com July 2010
BusinessForum
MILTON CHANG is founder and managing director of Incubic Management LLC. He is also director of Precision Photonics and mBio. Chang is a Fellow of IEEE, OSA, and LIA. He has received Distinguished Alumni awards from the University of Illinois and Caltech, is a trustee of Caltech, and is member of the Committee of 100. Contact Chang at [email protected] with questions, and visit www.incubic.com for other articles he has written regarding entrepreneurship.
Q
QA
A
I have been working on and off as a
consultant for a couple of compa-
nies since I lost my job almost two
years ago. Despite my extensive
project management experience
and reputation in the photonics
industry, I am unable to fi nd any
work recently. Any suggestions?
You may want to brand yourself as a
contractor instead of a consultant to
at least get a block of days at one time.
To many people, “consultant” implies a
high billing rate and intention to work
only sporadically—both of which are
not really the case. And given that we
are just coming out of a severe reces-
sion, companies are more likely to hire
temporary workers than permanent
employees to avoid increasing their
overhead costs just in case there is a
double dip in the economy. Also, it is
unlikely that companies will aggres-
sively pursue new projects that require
consultants at this point of the recovery.
You have to increase the number
of clients and get beyond the photo-
nics industry in order to get a stable
income and feel less impact from eco-
nomic cycles. Given the usefulness of
photonics, you should be able to fi nd
companies that want to apply photo-
nics but need your help.
You could first leverage your
reputation and the network of people
who are aware of your capability and
reputation. Generate a target list and
let your friends know your availability
and predicament. You can also
prospect broadly and promote your
credentials: Develop a web site and come up with ways for search engines to
fi nd you, attend conferences to renew acquaintances, talk to companies on the
exhibition fl oor, and even spend a few dollars to run an ad campaign (such as
using Google AdWords) for potential clients to fi nd you.
One other tactic that may be worth considering is to promote your exper-
tise and name recognition to help companies win contracts. You can boost the
likelihood of winning contracts by participating in writing proposals and by
lending your name to give the proposal more pizzazz. By getting written into
contracts, you are assured of work when the contract is awarded.
I would you like to discuss how to start a company to commercialize
my solar energy invention that I plan to patent.
In order to succeed, you must fi rst put in place all the necessary ingredients
for building a successful enterprise: technology, application, business model,
human and fi nancial resources… as well as leadership and management skills.
Having a patent is a good starting point but is no guarantee that the idea is
useful or the technology works.
Solar energy is a “hot area,” which also means risk increases exponentially
with time to market. What you don’t want to do is raise lots of money to try
to build out the company quickly to gain “fi rst mover” advantage. That is in
essence putting the cart before the horse, betting on a wing and a prayer, etc.,
that your assumptions are correct—a risky proposition, based on VC statistics,
with less than a 50/50 chance that you might succeed.
Now I will stick my neck out a bit to suggest what you might do. Work toward
an early acquisition by focusing resources to verify what a potential acquirer
might want to ascertain: The technology works, the product is manufacturable,
and customers want the product. Getting acquired is not easy but at least you
will be spending less to fi nd out earlier whether your idea is valuable. Adding a
feature to the product line of an established company could provide a competi-
tive advantage, and you may get a high valuation if several companies compete
for the ownership of your IP. And taking this approach does not deprive you
the opportunity to “go for it” if you fi nd your invention is a barnburner.
M I LT O N C H A N G
How can I develop my consulting business?
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________________________________
33Laser Focus World www.laserfocusworld.com July 2010
Sheetlike microplasma arrays have many applicationsJ. GARY EDEN and SUNG-JIN PARK
Plasma, also known as the fourth
state of matter, is a partially ionized
gas or vapor. Commercial applications
of plasmas include water purifi cation,
manufacturing of integrated circuits,
and curing polymers, but of all the in-
dustrial and residential uses of plasma,
displays and lighting are pre-eminent.
The rise of fl at-panel plasma TVs in the
past decade has been nothing short of
meteoric. However, despite the recent
emphasis by manufacturers on
decreasing the power consumption
and thickness of plasma and liquid-
crystal-display (LCD) TVs, the most
pressing long-term drivers of display
development continue to be dramatic
reductions in weight
and manufacturing
cost, as well as the
introduction of
fl exibility. The avail-
ability of an economi-
cal sheetlike fl exible
display that could be
hung on a wall, or wrapped around
curved surfaces, would allow video dis-
plays to be placed virtually anywhere
for a variety of applications.
In the realm of lighting, plasma
lamps have a dominant position by
generating several gigawatts of visible
light on a continuous basis worldwide,
or approximately 80% of all the light
produced by general illumination.
Although existing plasma lamps
boast favorable effi ciencies, virtually
all contain mercury and most
require ballast and have a fragile
glass envelope. The availability of a
thin, lightweight, inexpensive, and
nontoxic source of white light would
transform the landscape of residential
and commercial lighting.
Microcavity arrays
The emerging fi eld of microplasma
technology holds considerable promise
for the next generation of displays and
lighting. By shrinking a conventional
plasma lamp by three orders of
magnitude, microscopic plasmas
having the form of cylinders, ellipsoids,
or other shapes can be generated by the
thousands or millions in microcavities
By shrinking plasmas to microscopic
dimensions, thin light-emitting sheets
ideally suited for displays, specialty and
general illumination, environmental
remediation, and sterilization have
become a reality.
FIGURE 1. 20,000 microcavities
each have a parabolic shape
and green phosphor deposited
within the cavity (left top and
bottom). A 6 × 6 in. white
lamp has a thickness of a few
millimeters (top right). A small
array of microplasmas creates
UV emission from ordinary room
air (bottom right). (Courtesy of
the University of Illinois and Eden
Park Illumination)
FLEXIBLE DISPLAYS
CO
VE
R S
TO
RY
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July 2010 www.laserfocusworld.com Laser Focus World 34
FLEXIBLE DISPLAYS cont inued
fabricated in the surface of glass, aluminum (Al) foil, or even
plastic. Having sizes on the order of the diameter of a human hair,
these microcavities are built by processes largely developed by
the very-large-scale-integration (VLSI) and MEMs communities.
By successfully confi ning plasmas in arrays of microcavities,
researchers and engineers at the University of Illinois have
realized light-emitting sheets that are thin and inexpensive
and, in several instances, fl exible as well. At the heart of a
microplasma device is the microcavity itself, whose shape, in
addition to the surrounding materials determines the spatial
profi le of the electric fi eld within the cavity. Most of the micro-
plasma devices being pursued today are cylindrical with diam-
eters of 50 to 200 μm, but other cross-sectional shapes such as
diamond, rectangular, and pyramidal have also been created
and used successfully, and the smallest plasmas realized to date
were confi ned to cavities 5 μm in width.
A wide array of substrate materials, including silicon, glass,
high-k ceramics, polymers, and Al have been explored. After
sealing the device (or a large array of devices) with a window
material, a gas or mixture of gases is introduced to the cavity.
With proper design of the electrodes, the dielectric separating
them, and the cavity, a stable and bright glow discharge is
produced in the microcavity when a voltage (AC, DC, or pulsed)
is applied to the electrodes.
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_______________________________________
___________________________
35Laser Focus World www.laserfocusworld.com July 2010
Near-atmospheric pressure
Although in some ways similar to
plasmas in standard fl uorescent lamps,
microplasmas have several startling
properties. Because of their small cavity
dimensions, microplasma devices oper-
ate well at pressures of roughly one at-
mosphere, as opposed to the several
thousandths of an atmosphere that is
characteristic of fl uorescent lamps. This
property is valuable for several reasons,
one of which is that little or no pressure
differential exists across the window and
substrate of a microplasma lamp, thereby
allowing the overall package to be quite
thin and fl exible. A less obvious advan-
tage is the ability to produce effi ciently, in
large numbers and in situ, transient light-
emitting molecules not normally found in
nature (such as excited diatomic xenon or
argon deuteride).
Another surprising characteristic of
microplasmas is the steady-state power
loading, or power density (electrical power
deposited in the plasma per unit volume),
which often reaches tens of kilowatts
per cubic centimeter; values as high as 1
MW/cm3 have been realized. Such excita-
tion levels are extraordinary and, in fact,
unprecedented for continuous operation of
macroscopic plasmas. For comparison, the
power loading of fl uorescent lamp plasmas
is typically tens to hundreds of milliwatts
per cubic centimeter.
To meet the need for inexpensive,
large-area display and lamp technology,
arrays of microplasma devices built into
Al foil were fi rst tested successfully four
years ago at the University of Illinois;
the development curve has been steep
ever since. Aside from the low cost of
Al foil itself, a strong attraction of this
technology is the automatic formation of
array electrodes and interconnects by a
wet chemical process.
Beginning with a single sheet of Al foil
having a thickness of nominally 120 μm,
holes or cavities 30 to 200 μm in diameter
are produced in the foil in the desired
pattern by etching. In a subsequent
electrochemical process, virtually all of
the Al in the original foil is converted into
translucent, nanoporous Al oxide (Al2O3).
This carefully controlled wet process
forms electrodes around the microcav-
ities and the electrical interconnects
between microcavities while simultane-
ously burying the microplasma devices
in a thin layer of Al2O3.
Converting aluminum to alumina
If the cavity-to-cavity spacing (pitch)
and chemical-processing parameters are
chosen properly, the electrodes for all
of the microcavities in a line (or a two-
dimensional pattern, if desired) are inter-
connected automatically. A modifi cation
of this process provides the ability to
precisely control the cross-sectional geom-
etry of a cavity, thereby opening the door
to shaping the electric fi eld throughout
the microplasma while also optimizing
the extraction of light from the cavity. For
example, an array of 20,000 micro-emit-
ters, each having a parabolic cross-section
and an emitting aperture of 160 μm, has
been fabricated (see Fig. 1). This array has
a radiating area of about 25 cm2 and, al-
though originally a 120 μm thick sheet of
ordinary Al foil, has been almost entirely
converted into transparent alumina. The
green luminescence from the array is the
result of injecting a commercial phosphor
into each microcavity and illuminating
the array with weak ultraviolet light.
Such arrays are the building blocks
for displays and lamps. Microplasma
lamps as large as 900 cm2 in active
(radiating) area have been built and
tested to date but development at Eden
Park Illumination is focusing on 6 × 6 in.2
(230 cm2) and 8 × 8 in.2 (400 cm2) white
lamps. Having a thickness of only a few
millimeters, these fl at lamps are powered
by plasmas produced within cavities in
a phosphor and alumina-overcoated Al
mesh. A carefully balanced mixture of
red, green, and blue phosphors converts
ultraviolet emission generated by the rare-
gas plasmas into white light. Although
optimizing the cavity design and other
aspects of the lamp’s construction is in
progress, the luminous effi cacy (optical
effi ciency, expressed in units of lumens/
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_____________________
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______________________
LightMachinery www.lightmachinery.com
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37Laser Focus World www.laserfocusworld.com July 2010
FLEXIBLE DISPLAYS cont inued
watt) of these fi rst-generation lamps
easily exceeds that of incandescent lamps,
and laboratory prototypes are yielding
effi cacies beyond 30 lumens/W.
Arrays of microplasmas are also
promising for environmental applications
such as the purifi cation of
air or ozone production. A
small array has been made
that operates continuously
in ordinary room air, for
example, a feat which is
extraordinarily challenging
with conventional
(macroscopic) plasma
technology. By producing
intense but uniform
glow discharges in air,
biological contaminants
can be destroyed and
pollutants or greenhouse
gases converted into other,
more useful forms.
It is f lexibility,
however, that may well
be the most appealing
aspect of microplasma technology.
Displays made by sealing microplasma
arrays within thin plastic sheets are
both fl exible and transparent, such as
shown in the low-resolution prototype
in Fig. 2. Cavities and gas-connecting
channels are stamped into the plastic
substrate by a process known as replica
molding; addressability of all the pixels
in such arrays has been achieved. With
this development, lightweight wall-sized
plasma TVs can be envisioned that could
ultimately lead to widespread adoption
of virtual-reality environments.
J. Gary Eden and Sung-Jin Park are profes-
sors of electrical and computer engineering at
the University of Illinois, 1406 W. Green, Urba-
na, IL 61801, and cofounders of Eden Park Il-
lumination, 903 N. Country Fair Dr., Champaign,
IL 61821; e-mail: [email protected]; www.
edenpark.com.
Tell us what you think about this article. Send an
e-mail to [email protected].
FIGURE 2. A fl exible and transparent display is based on
microplasmas sealed within two thin plastic sheets. Ultraviolet
emission produced by the plasmas excites a phosphor within
each cavity. (Courtesy of the University of Illinois and Eden
Park Illumination)
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___
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___________________
Laser crystal
Conductive cooling
Radial thermal gradient
Pumplight
39Laser Focus World www.laserfocusworld.com July 2010
Femtosecond amplifi er output gets a boostSTEVE BUTCHER and MARCO ARRIGONI
Numerous applications in applied
physics and chemistry are driving a
demand for ultrafast amplifi ers that
deliver femtosecond pulses at higher
repetition rates and average power to
increase signal-to-noise ratios and re-
duce data acquisition times. Delivering
this performance without sacrifi cing
pulsewidth, beam quality, operation-
al simplicity, or reliability has proven
to be a challenge. Recent design im-
provements now enable a system that
yields up to 15 W of average power us-
ing only thermoelectric (TE) cooling of
the Ti:sapphire gain medium. Previous-
ly, these output power levels required
cryogenic cooling, resulting in complex
and space-consuming systems.
The need for power
The Ti:sapphire-based modelocked laser
oscillator revolutionized applications
of ultrafast lasers, simplifying access
to femtosecond pulses. A typical
Ti:sapphire oscillator delivers average
powers up to 2–4 W. At
repetition rates of 50–
100 MHz, the pulse
energy is at most a
few tens of nanojoules,
with a peak power of
about 500 kW, depending on the pulse
duration.
Many applications require much
higher pulse energy or peak power,
a need met with chirped pulse ampli-
fi cation (CPA). The oscillator pulses
are stretched, selected by an appro-
priate pulse picking device, ampli-
fi ed by several orders of magnitude
in another Ti:sapphire crystal, then
recompressed to pulsewidths almost
as short as the initial pulses.
Amplifi ed femtosecond pulses can
be used to pump one or more tunable
optical parametric amplifi ers (OPAs)
for pump-probe studies in solid-state
physics and photochemistry. They can
also be used to generate THz pulses
for imaging or spectroscopy. More
recently, the availability of amplifi ed
systems featuring carrier to envelop
phase (CEP) stabilization opened the
door to the production of attosecond
pulses at extreme UV (4–30 nm) wave-
lengths—pulses that are short enough
to study the dynamics of electrons in
atoms and molecules.
Many of these applications involve
one or more cascaded or parallel non-
linear conversion stages (parametric
Advanced ultrafast amplifi ers combine
high power, excellent beam quality, and
high repetition rates in a turnkey system
without cryogenic cooling.
FIGURE 1. End-pumping a
Ti:sapphire laser rod with a circular
pump beam creates a radial
thermal gradient that acts like a
strong spherical lens.
ULTRAFAST LASERS
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www.nanoplus.com email: [email protected] phone: +49 (0) 931 90827-0 fax: +49 (0) 931 90827-19
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conversion or other effects) that are often
relatively ineffi cient. Thus, increasing the
amplifi er energy per pulse offers the capa-
bility to effi ciently drive multiple, high-
energy, nonlinear stages in parallel.
Thermal lensing
A major technical hurdle in scaling ul-
trafast amplifi er systems to higher pow-
er is thermal lensing (distortion) in the
gain crystal. Even with laser pumping,
more than 75% of the pump power is
converted into heat. End-pumping the
Ti:sapphire rod creates a radial power
distribution where maximum pump in-
tensity is delivered along the center line
of the gain medium. Local heating in the
Ti:sapphire crystal follows the intensity
pattern of the pump light and the crystal
FIGURE 2. In a regenerative amplifi er an
injected pulse makes many trips around the
amplifi er cavity before being released via an
acousto-optic switch.
Output beam characteristics using regenerative amplifi er
Regen + Power amp (1 kHz) Output power (W) M² (x) M² (y)
Single-pass 8.0 1.09 1.08
Double-pass 10.2 2.09 1.60
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Sales Offices:North America and Asia: dial USA +1 310-978-0516Europe: dial Norway +47-3-303-0300Email: [email protected] www.osioptoelectronics.com
Engineering Custom andStandard Optoelectronics
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Light Sensing Ideas
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Corporate Headquarters: 3280 East Foothill Boulevard, Pasadena, CA 91107-3103 (626) 795-9101Fax (626) 795-0184 E-mail: [email protected] Web: www.opticalres.comOffi ces: Tucson, AZ | Westborough, MA | Pittsford, NY
©2010 Optical Research Associates. LightTools is a registered trademark of Optical Research Associates.
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Richardson Gratings –A Leader for Over 60 Years• World's largest selection of ruled and holographic diffraction
gratings for industrial and scientific applications
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©2010 Newport Corporation
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43Laser Focus World www.laserfocusworld.com July 2010
is conductively cooled via its mounting surface(s). The end re-
sult is a radial thermal gradient perpendicular to the direction
of the laser beam (see Fig. 1). Even a pump power of just 10 W
and a beam waist of 50 μm, for instance, can result in a thermal
lens of more than 50 diopters. With pulsed pump lasers avail-
able at 40 W and higher, this lensing effect becomes the single
largest design challenge.
There are several ways to cool a Ti:sapphire crystal, thereby
reducing the strength of the thermal lens effect. Unfortunately, the
effectiveness of these cooling methods scales with their cost and
complexity. Passive conductive cooling is the simplest method, fol-
lowed by water cooling. These approaches are practical for pow-
ers up to 3–4 W. In higher-performance systems, the Ti:sapphire
crystal is usually cooled with a TE cooler, but until recently even
with this method the maximum average power was 7–8 W.
The ultimate approach is to use cryogenic cooling. At these
low temperatures the thermal conductivity of Ti:sapphire
increases roughly 40 times and the dependence of refractive
index on temperature drops by an order of magnitude. The net
result of these two effects is about a 400 times decrease in ther-
mal lens power between a Ti:sapphire crystal at 300 K and one
cooled to 77 K. Until now, all amplifi ers producing more than
a few watts were cooled cryogenically, with disadvantages in
terms of cost and complexity.
ULTRAFAST LASERS cont inued
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SAVE THE DATESeptember 26-30, 2010 ANAHEIM MARRIOTT • ANAHEIM, CALIFORNIA
LASER APPLICATIONSPOWERING THE RECOVERY
ICALEO® brings together the leaders and experts in the field of laser materials interaction, providing the world’s premier platform
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Pump
Thermallensing effect
Incomingamplified IR beam
Normal beam divergence
ULTRAFAST LASERS cont inued
A 15 W system
Diverse applications concur to make
highly desirable a 15 W class amplifi er
with the same simplicity and beam qual-
ity as a 3–4 W system.
We chose a hybrid design to deliver the
beam quality of a regenerative amplifi er
without the cost and complexity of cryo-
genic cooling. Specifi cally, the Coherent
Legend Duo HP uses a regenerative ampli-
fi er followed by a single-pass amplifi cation
stage, all in the same box, with TE cooling
for both Ti:sapphire crystals.
This approach is different from multi-
pass amplifi cation where the input pulses
pass about 10–15 times through the crys-
tal, with each pass at a slightly different
angle but providing some overlap with
the pump beam. Such a system is opti-
cally complex and results in beam quality
and pointing that is degraded compared
to the seed laser beam quality. In con-
trast, a regenerative amplifi er is a high-
gain laser cavity where pulses from the
seed laser are amplifi ed during numer-
ous round-trips and, upon reaching gain
saturation, are coupled out of the cav-
ity (see Fig. 2). The output beam charac-
teristics of the amplifi er are independent
of the seed laser, governed by the simple
cavity design, and produce a near-perfect
TEM00 mode with stable pointing char-
acteristics suited for downstream nonlin-
ear generation processes. The additional
single-pass power amplifi er is simple and
maintains the beam quality of the regen-
erative amplifi er.
With an integrated pump laser split
between the two Ti:sapphire crystals,
this regenerative plus single-pass ampli-
fi er can deliver more than 8 W at 1 kHz
and 12.5 W at 5 kHz. For the high aver-
age pump powers involved, thermal lens-
ing is not trivial but can be reduced to a
manageable level by using specially shaped
crystals with fl at, larger mounting surfaces
FIGURE 3. Using a single-pass amplifi er (SPA) to boost the output of the regenerative
amplifi er means thermal aberrations are only experienced once resulting in excellent beam
quality. Even just two passes would degrade the beam quality.
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0
0.2
0.4
0.6
0.8
1
1.2
0 0.5 1 1.5 2 2.5 3 3.5 4
Re
sp
on
se
36
24
12
48 dB/octave
Bessel
Time (ms)
-60
-50
-40
-30
-20
-10
0
100 Hz 1 kHz 10 kHz
12 dB/octave
24
36
48 dB/octave
Bessel
Re
sp
on
se
[d
B]
-60
-50
-40
-30
-20
-10
0
100 Hz 1 kHz 10 kHz
12 dB/octave
24
36
48 dB/octave
Frequency
Re
sp
on
se
[d
B]
Butterworth
0
0.2
0.4
0.6
0.8
1
1.2
0 0.5 1 1.5 2 2.5 3 3.5 4
Time (ms)
Re
sp
on
se
36
12
48 dB/octave
Butterworth24
Bessel and Butterworth Filters
The SIM965 Analog Filter is ideal forapplications where Bessel or Butterworthfilters are needed. High-pass and low-passfiltering are both included, with up to48 dB/octave rolloff. The cutoff frequencymay be set with 3-digit resolution.
Up to eight SIM965 modules can behoused in one SIM900 mainframe.Mainframes can be cascaded, allowing anunlimited number of filter channels.
All SIM965 functions can be programmedfrom a computer through the SIM900mainframe. RS-232 and GPIB interfacesare supported.
• 1 Hz to 500 kHz
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• Continuous time filter
SIM965 ... $1095 (U.S. list)
Stanford Research Systems
All filters shown tuned to 1 kHz cutoff
(408)744-9040
www.thinkSRS.com
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©2010 Newport Corporation
Make the Impossible, Possible With Newport Replicated Mirrors
Need to minimize system cost? Locate a mirror in an otherwise inaccessiblelocation? Design the exact optical instrument you want? Newport OpticonReplicated Mirrors can help you accomplish these seemingly impossible missionsand more.
A great alternative to conventional optics, these mirrors are typically made of low-cost metal and ceramic substrates, providing both the design andmanufacturing flexibility to:
• Reduce instrument weight and size • Increase instrument stability• Improve ease of assembly• Drive down instrument costs
Newport’s Opticon Mirror Products team has many years of experience designingand manufacturing creative solutions for OEM applications. To see what’s possible,visit us at www. newport.com/mirrors-5 or call 1-800-598-6783.
July 2010 www.laserfocusworld.com Laser Focus World 46
ULTRAFAST LASERS cont inued
instead of the typical cylindrical
laser rod shape. The crystals are
then cooled through the fl at sur-
faces by TE coolers in a proprie-
tary highly conductive mount.
To boost the regenerative ampli-
fi er output to 15 W, we add a sec-
ond, external pump laser. The
optical setup of the regenerative
plus single-pass amplifi er is essen-
tially unchanged but the output
power is boosted to greater than
10 W at 1 kHz, 15 W at 5 kHz,
and 12 W at 10 kHz. With either
one or two pump laser confi gu-
rations, the one-pass fi nal ampli-
fi er stage does not affect the beam
pointing and TEM00 beam pro-
fi le that are key characteristics of a
regenerative amplifi er. Laboratory
tests show that this is an optimum
setup (see Fig. 3). Increasing the
number of passes from 1 to 2 only
modestly increases the overall out-
put power (by about 20%) but increases
the beam M2 value by nearly 100%. By
maintaining a low M2 value in a single-
pass setup, the design combines optical
simplicity and effi ciency with the ideal
beam characteristics for focusing into hol-
low fi ber cores or pumping multiple high-
energy OPAs, and eliminates the need for
complex cryogenic cooling (see Fig. 4).
Ultrafast amplifiers are usually
selected based on parameters like energy
per pulse, repetition rate, and mode
quality. As the experiments become
more complicated, turnkey reliability
and ease of use become increasingly
important. Design refi nements make it
possible to improve fl exibility and per-
formance, along with simplicity and
turnkey operation.
Steve Butcher is marketing manager for Re-
search Laser Systems and Marco Arrigoni is
director of marketing for the Scientifi c Market
at Coherent Inc., Santa Clara, CA; e-mail: steve.
[email protected], www.coherent.com.
FIGURE 4. Excellent beam quality enables higher
effi ciency and quality of nonlinear processes
like parametric amplifi cation and harmonic and
continuum generation. When an amplifi ed pulse
is focused into a sapphire plate (or hollow fi ber),
cascaded nonlinear effects create a supercontinuum
of light, shown here dispersed by natural diffraction.
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By listening to customers and designing solutions to fit their needs, GSI have a wide range of lasers, process
tools and options to make JK Lasers a great fit for your industrial manufacturing requirements.
The JK Fiber Laser range includes:
• Air and water cooled fiber lasers up to 400 Watts
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To see how JK lasers can be a flexible solution for your processing requirements contact us at our
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Single pixel detector
Beamsplitter
Objective
Collimatinglens
Relay lens
Illumination source
Excitation filter
Emission filter
“On” pixel “Off” pixel
DMD
Specimen
July 2010 www.laserfocusworld.com Laser Focus World 48
Optical-sectioning microscope uses a single-pixel detectorJOHN WALLACE, senior editor
Confocal microscopy, in which the
image of a point source is scanned
across the specimen and the collect-
ed light fi ltered by a pinhole to block
the out-of-focus light, allows a 3D
image of the specimen to be built up
point by point—a valuable property
for both science and industry. In the
latter, the technique is widely used to
image and inspect the patterns manu-
factured on semiconductor chips.
The scanning in an ordinary con-
focal microscope (CM) requires a
mechanically moving stage or other
device to move the focal spot relative
to the specimen. In contrast, a pro-
grammable-array microscope (PAM)
contains, somewhere within its optical
train, an array with pixels that can be
switched on and off in
individual sequence
to mimic a mechani-
cally scanned point of
light. The array can
be a digital-micro-
mirror device (DMD),
liquid-crystal-on-sili-
con (LCoS), or other type of 2D pro-
grammable array; such devices usually
allow scanning at kilohertz rates. A
PAM also requires a second 2D imag-
ing array precisely aligned to the fi nal
image of the programmable array.
Compressive sensing
The complexity of the PAM optical
system has led researchers at the Uni-
versity of Delaware (Newark, DE) to
simplify things by applying a tech-
nique called compressive sensing (CS),
in which many pixels on the pro-
grammable array are switched on at
the same time in different predeter-
mined patterns and all the light from
the specimen collected at once; sub-
sequent calculations derive the image
A programmable-array microscope relies
on a digital-micromirror device and a
sampling technique called compressive
sensing to take 2D slices of 3D objects,
all the while collecting light with just a
single detector.
FIGURE 1. A pixel pattern on a DMD forms a
modifi ed scrambled-block Hadamard ensemble;
black is “off” and white is “on” (left). No two
adjacent pixels are ever on at the same time
(the black areas between any two nearby pixels
are actually “off” pixels). The illumination source
for the SP-PAM is imaged onto the DMD at a
24° angle (right) so that, in the mirrors’ “on” state,
the illumination follows the optical axis, which is
normal to the DMD.
SCANNING OPTICS
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Bottom surface of the etched holes Top surface of the sample
8 μm
Horizontal
plane
10 μm
20 μm
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49Laser Focus World www.laserfocusworld.com July 2010
from the results.1 Using CS allows the
second array (the 2D imaging array) to
be eliminated and a single detector to
be used instead.
The pixel patterns for CS must be
carefully designed so that they effi -
ciently collect the data for the subse-
quent calculations; each pattern must
have no two adjacent pixels on at the
same time; and in combination the pat-
terns should include every pixel of the
array. The researchers chose to use pat-
terns called modifi ed scrambled-block
Hadamard ensembles (see Fig. 1).
Design and model
In the experimental single-pixel (SP)
PAM system, light from an incoherent
(tungsten-halogen) illumination source is
introduced to a DMD programmable array via a beamsplit-
ter and a relay lens; the illumination intensity across the ar-
ray is approximately uniform. The DMD is in turn imaged
onto the specimen via a collimating lens and a microscope
objective with 40X magnifi cation and a numerical aperture
(NA) of 0.65. Light collected from the specimen takes the
path back through the system, passing through the beam-
splitter to a single-pixel detector.
The DMD has frame rates of up to 8000 frames per sec-
ond. Each micromirror in the DMD has an off position of
-12° and an on position of 12° from the normal of the DMD;
as a result, the illumina-
tion light for the SP-PAM
is introduced at 24° from
the normal so that the mir-
rors refl ect the light at 0°
when in the “on” state.
The researchers mod-
eled a simplifi ed version
of their system with an
optical-design program
to examine the trans-
fer functions of versions
of the PAM architecture
with differing parame-
ters. They concluded that
a smaller DMD pitch (relative to the illumination wavelength)
results in a more-widespread transfer function, meaning a
narrower impulse response and thus a smaller single-pixel
illumination size on the image and better resolution. In addi-
tion, they found that the transfer functions had some so-
called blind spots, which could mean that the DMD-based
SP-PAM does not resolve some spatial-frequency components.
Discerning texture
The researchers used the SP-PAM to generate 2D optical sec-
tions of a dry-etched silicon sample (see Fig. 2). The sample
had etched holes about 8 μm deep with rough sidewalls and
FIGURE 2. Using the SP-PAM, optical cross-sections were taken of a patterned silicon
sample (drawing, top right). The sections were 2 μm apart (bottom, left to right). In addition,
a control image was taken with a CCD replacing the single detector and with all the DMD
mirrors “on” (upper left). (Courtesy of the University of Delaware)
Optical-Sectioning continued on page 55
A smaller DMD pitch
(relative to illumi-
nation wavelength)
results in a more
widespread transfer
function, a narrower
impulse response, and
a smaller single-pixel
illumination size.
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Helicalside core
Central core
Cladding
r
Λ
φ
51Laser Focus World www.laserfocusworld.com July 2010
Structured fi ber advances short-pulse laser performancePHILL AMAYA
A growing number of high-precision
materials processing applications re-
quire short-pulse lasers. Such appli-
cations include microvia hole drilling
in PCBs and fl ex circuits, semicon-
ductor memory repair, solar cell
edge isolation and thin-fi lm pattern-
ing, and sapphire substrate scribing
in LED manufacturing.1 All of them
are characterized by increasing min-
iaturization and/or relentless pressure
to reduce manufacturing costs.
Miniaturization and diminishing
feature size are the primary reasons
for using short-pulse lasers. Pulse
lengths of less than 80 ns are
typically required to mini-
mize the heat-affected zone
at the work piece and con-
sequent potential damage to
nearby components. Micron-
scale features also favor
shorter wavelengths because
these wavelengths can achieve
a smaller focused spot size.
Material absorption charac-
teristics are also a key con-
sideration in determining laser
wavelength.
In addition, as feature sizes
diminish, there are more fea-
tures to process per device
or per unit area so
laser pulse repetition
rate must increase or
manufacturing cycle
time per device will
grow. This require-
ment is amplified
when the substrate upon which fea-
tures are fabricated simultaneously
increases in size. The minimum fea-
ture dimension of a semiconduc-
tor memory chip, for example, has
fallen from 150 to 60 μm over the last
10 years. At the same time the sili-
con wafer has increased in size
from 200 to 300 mm. Hence the
possible number of features that
can be printed on a single wafer
has jumped by a factor of 14.
In this example, the reduction
in feature size has also driven
the process to adopt UV wave-
lengths for a smaller spot size. These
advances have driven laser develop-
ers to increase average output power
by a factor of 10 at the fundamental
wavelength of around 1.0 μm while
migrating the application wave-
length to 355 nm. Similar trends
are evident in other microelectron-
ics applications. Solar cell processing
is driven by increasing surface areas
and reducing processing time.
The vast majority of nanosecond-
pulse applications today are served
by diode-pumped solid-state (DPSS)
Chirally coupled core fi ber enables
scaling of single-mode fi ber core size—
essential for the high peak power laser
operation needed in high-precision
materials processing applications.
FIGURE 1. Chirally
coupled core fi ber
uses a central
guiding core with at
least one satellite
core wrapped
helically around it.
Inset photo shows
fi ber endface.
FIBERS FOR FIBER LASERS
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Helix period (mm)
Loss (dB/m)
10987
1000
100
10
1
0.1
LP31LP21LP11
LP01
LP02
Preform spinningand fiber pulling
during fabrication
Fiber preformmade with on-axiscentral core and
off-axis satellite core
Fabricated3C fiber
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July 2010 www.laserfocusworld.com Laser Focus World 52
FIBERS FOR FIBER LASERS cont inued
lasers. The performance of these systems
refl ects more than 20 years of continu-
ous innovation and is largely unmatched
by any other laser technology. There are
signs, however, that some applications
may be advancing beyond
the practical capabilities of
DPSS lasers. Smaller spot
requirements and material
issues are driving pulse
lengths to the picosec-
ond regime, but the nec-
essary per-pulse energy
must be maintained even
as pulse repetition rates
increase. Creative solu-
tions are emerging, such
as “dual-beam” technol-
ogy where the output
from two pulsed sources
is multiplexed to deliver
twice the pulse repetition
rate. Another “hybrid”
approach is based on a
low-power, high-pulse-
repetition-rate fi ber laser
that seeds a DPSS ampli-
fi er in an approach that
splits the pulse genera-
tion work from the power
amplification. Though
these solutions are being
deployed, they do add cost
and complexity, and their
path for additional scaling
may be somewhat limited.
Fiber lasers
Among the solutions pro-
posed for a next-genera-
tion source to address
current and developing
short-pulse applications is the fi ber la-
ser. Key target specifi cations are sum-
marized in the table. Fiber lasers are
attractive for short-pulse applications
because of their high single-pass gain,
which enables simple amplifi er designs
and straightforward average power
scaling. The diffi culty comes in scal-
ing the fi ber core size for the high-peak-
power operation needed to achieve the
required pulse energy and duration.
Without core size scaling, nonlinear
optical effects cause spectral broaden-
ing and output power instabilities. Us-
ing 20 μm core double-clad fi ber (DCF),
FIGURE 2. Calculated modal loss for a specifi c 3C fi ber design
with core diameter of 35 μm shows that for a helix period of 9
mm, loss of less than 0.2 dB/m is achieved for the fundamental
LP01 mode and more than 100 dB/m for higher order modes.2
Target specs for fi ber lasers
Beam quality TEM00 (M2 <1.1)
Pulse energy 1.0 mJ (@10–100 kHz)
Pulsewidth 10 ns (10–100 ideal)
PolarizationLinear with polarization
extinction ratio ≥100:1
Spectral width <1 nm
Average power Up to 100 W
FIGURE 3. Spinning the 3C fi ber preform while it is drawn
causes the off-axis core to spiral around the central core
producing the desired helix.
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__________
Absorbed pump power (W)
Signal power (W)
120 16080400
120
90
60
30
0
z position (mm)
Beam diameter (μm)
60 80 10040
30 W
M2 = 1.07
200
900
700
500
300
100CALL
1-800-374-6866
or VISITwww.photon-inc.com/nist
“I don’t think I
can continue
guessing about
my laser’s
performance.”
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uncertainty
with Photon
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beam profilers
Laser Focus World www.laserfocusworld.com
commercial fi ber lasers available today
promise up to 25 kW of peak power in
a 10 ns pulse, yielding 25 W of average
power at 100 kHz operation. This is
only one-quarter of the average pow-
er targeted in the table and about half
of what current DPSS lasers can deliv-
er. A promising solution with poten-
tial for further power scaling involves
a uniquely structured fi ber
named chirally coupled
core or 3C fi ber.2
This 3C fi ber enables
single-mode optical out-
put from fi bers with core
diameters much larger
than conventional double-
clad, large-mode-area fi ber.
Chirally coupled core fi ber
consists of a central guid-
ing fi ber core and at least
one satellite core wrapped
helically around the cen-
tral core (see Fig. 1). This
structure is designed to
selectively couple higher-
order optical modes from
the central core to the side
core, while propagating
only the fundamental LP01
mode in the central core.
Specifi cation of the appro-
priate side core parameters
and helical period results
in high loss for the modes
coupled into the side core,
which are scattered into
the cladding. This concept
can be applied to very-large-core fi ber
designs (see Fig. 2).
Fabrication of 3C fi ber is straightfor-
ward with two basic differences from
standard DCF production. Standard
DCF is drawn from a glass rod, known as
a preform, with an appropriately doped
center core. The dimensions of the pre-
form and its core are constructed so they
converge to the desired fi ber dimensions
when heated and drawn on a fi ber tower.
To make 3C fi ber the preform includes
two doped cores. One core is on the pre-
form central axis and one slightly off axis.
Next, when the fi ber is drawn it is spun.
This spinning causes the off-axis core to
spiral around the central core producing
the desired helix (see Fig. 3).
An important attribute of 3C fi ber is
that its performance does not depend
on specifi c bending. This is in contrast
to standard large-mode-area fi bers that
achieve single-mode performance by
FIGURE 4. Tests on the 3C fi ber demonstrate its slope
effi ciency (70%) and beam quality. Here the fi ber achieved
an M2 of 1.07.4
Fiber lasers are
attractive for short-pulse
applications because of
their high single-pass
gain, which enables
simple amplifi er designs
and straightforward
average power scaling.
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TUNING FORK
CHOPPERSTuning fork choppers are suitable
for long life dedicated applications,
OEM, built into an instrument or a
portable system.
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APPLICATIONS INCLUDE: FEATURES:
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Products You Trust ... Performance You Deserve ... Prices You Expect
Temperature (°C)
Polarization extinction ratio (dB)
45 55 7565352515
25
20
15
10
5
0
July 2010 www.laserfocusworld.com Laser Focus World 54
careful coiling to exploit the
differences in bend-induced
losses between the funda-
mental mode and higher-order
modes—a method that’s effec-
tive up to about 25 μm core
diameters. For larger core
sizes it becomes increasingly
ineffective.3 This technique
is also problematic for beam
delivery and use in fi ber com-
ponents. Since modal discrim-
ination is not a function of fi ber bending,
3C fi ber can be used effectively in coiled
or straight confi gurations with active or
passive fi bers.
Chirally coupled core fi bers with core
diameters of 35 μm have been made with
and without ytterbium (Yb3+) doped
cores for use as gain fi bers and in the
construction of passive fi ber compo-
nents. Laboratory testing of fi ber per-
formance in a MOPA (master oscillator
power amplifi er) confi guration has pro-
duced more than 100 W of average
power, with 10 ns pulses and 100 kW
peak power at 100 kHz pulse repetition
rate (see Fig. 4).4
Polarization
It is important to recognize that the larg-
est applications for short-pulse lasers re-
quire visible and UV wavelengths, so a
suitable fi ber laser source must have sta-
ble polarization output. Polarized light
from optical fi bers is typically created by
strong birefringence resulting from di-
rectionally oriented material stress. This
can be achieved with stress rods in the fi -
ber and works well for fi ber core diame-
ters of less than 10 μm. As fi ber core size
increases it becomes more diffi cult to
produce uniform stress across the larg-
er cross-section of the fi ber core, mean-
ing that achieving high polarization
contrast is also diffi cult. The resulting
polarization performance is very sensi-
tive to thermal and mechanical pertur-
bations, which creates output instability.
In contrast, 3C fi ber designs have
been developed that exploit the manu-
facturing process and fi ber structure to
produce very low birefringence fi bers.
These low-bi fi bers very faithfully
reproduce at their outputs the polariza-
tion state of the input light (see Fig. 5).
Shrinking component features and
relentless pursuit of lower manufactur-
ing costs will continue to drive demand
for higher-performance, short-pulse
lasers. Our 3C fi ber is one of the most
recent innovations that can enable lasers
to meet those demands with scalabil-
ity for further performance advances.
Larger-core single-mode fi bers offer
performance potential that extends
well beyond the trajectory of current
applications in materials processing.
Three examples where applications
focused research is already underway
using 3C fi ber are 1) directed energy
weapons, 2) laser-produced plasma
extreme UV lithography, and 3) ultra-
fast spectroscopy.
FIBERS FOR FIBER LASERS cont inued
FIGURE 5. As linearly polarized
light is launched into a 4 m
length of coiled 3C fi ber, the
polarization state of transmitted
light was monitored while the
fi ber was heated from 20° to
70°C. There was no rotation of
the polarization axis and the
polarization extinction remained
above 20 dB. This performance
was also found to be robust
under signifi cant mechanical and
thermal perturbations.
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______
ELECTRO-OPTICAL PRODUCTS CORP.
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55Laser Focus World www.laserfocusworld.com July 2010
In directed energy applications, larger fi ber cores are needed
to achieve targeted CW powers while maintaining narrow spec-
tral width with single polarization. Fiber lasers are desirable here
because of their high electrical-to-optical effi ciency, compact size,
and potential for more robust assembly. Extreme UV lithography
is moving toward high-volume semiconductor production based
on large CO2, pulsed laser sources. Research based on large-core
single-mode fi bers suggests a more effi cient, compact, and scal-
able laser source might be constructed by spectrally combining
high-power pulsed fi ber lasers.5 Finally, large-core, single-mode
fi ber is a key element in efforts to make a compact and robust
source for practical ultrafast spectroscopy systems.
REFERENCES
1. S. Geiger, “Tailoring the performance of q-switched, solid state lasers – why
and how,” Solid State Lasers XV: Technology and Devices, Proc. SPIE, Vol.
6100, pp. 458–466 (2006).
2. A. Galvanauskas, M.C. Swan, C.H. Liu, “Effectively-Single-Mode Large
Core Passive and Active Fibers with Chirally-Coupled-Core structures,”
CLEO/QELS Conf. and Photon. Appl. Sys. Technol., OSA Technical Digest
(CD), Optical Society of America, paper CMB1 (2008).
3. M. Li, X. Chen, A. Liu, S. Gray, J. Wang, D. Walton, L. Zenteno, “Effective
Area Limit for Large Mode Area Laser Fibers,” OFC/NFOEC, OSA Technical
Digest (CD), Optical Society of America, paper OTuJ2 (2008).
4. C. Liu, S. Huang, C. Zhu, A. Galvanauskas, “High Energy and High Power
Pulsed Chirally-Coupled Core Fiber Laser System,” in Advanced Solid-Sta-
te Photonics, OSA Technical Digest Series (CD), Optical Society of America,
paper MD2 (2009).
5. K.-C. Hou, S. George, A.G. Mordovanakis, K. Takenoshita, J. Nees, B. Lafon-
taine, M. Richardson, and A. Galvanauskas, “High power fi ber laser driver
for effi cient EUV lithography source with tin-doped water droplet targets,”
Opt. Exp. 16, pp. 965–974 (2008).
Phill Amaya is CEO of Arbor Photonics Inc., Ann Arbor, MI 48105; e-
mail [email protected]; www.arborphotonics.com.
Tell us what you think about this article. Send an e-mail to LFWFeedback@
pennwell.com.
Optical-Sectioning continued from page 49
bottom surfaces; the sample itself was tilted slightly with
respect to the image plane due to a tilt in the sample stage.
In addition to optical sections, a “control” image was taken
with the single-pixel detector replaced with a CCD array and
with all the DMD mirrors turned on.
The neighboring sections were 2 μm apart from each other
along the optical axis. When compared to the control image,
the optical sections show more contrast between the rough
and smooth portions of the sample, thus better revealing the
variations in surface texture.
Gonzalo Arce, one of the researchers, notes that for fi ner reso-
lution, higher-NA objective lenses can easily be used in the setup.
“In terms of the next step in the experimental setup, we plan
to extend the current single-path architecture to a dual-path
compressive confocal architecture,” he says. “In a single-path
mode, we use the conjugate image only. The dual-path compres-
sive confocal microscope (CCM) exploits both the conjugate
and the nonconjugate images. The dual-path CCM, in theory,
allows us to simultaneously reach signal-to-noise-ratio values
and acquisition times that are not possible with other existing
confocal microscopy systems. In addition, we are modifying a
scientifi c-grade microscope into a CCM system. This upgrade
will give us more-convenient interfaces to different objective
lenses, better optical-alignment accuracy, lower noise contami-
nation, and a more rigid system construction.”
REFERENCE
1. Y. Wu et al., “A single-pixel optical sectioning programmable-array micro-
scope,” SPIE Photonics West 2010, Conference 7596, Jan. 27, 2010.
Tell us what you think about this article. Send an e-mail to LFWFeedback@
pennwell.com.
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Linear arraydetector
α
Matrix array(CCD)
α
57Laser Focus World www.laserfocusworld.com July 2010
Prism-based spectrometers tackle today’s miniaturization requirementsJEREMY LERNER
It is truly said that form follows func-
tion; however, increased miniaturiza-
tion inevitably collides with practical
realities. Surprisingly, however, tech-
nologies over 300 years old are fi nally
experiencing a rebirth in cutting-edge
applications. Sir Isaac Newton fi rst de-
scribed the use of a prism to display the
colors present in the sun’s light in 1666.
This promising beginning was soon
usurped by the diffraction
grating and by the late 1800s
grating-based spectrometers
became the de facto stan-
dard. But by the year 2000,
grating-spectrometer de-
velopment had more or less
hit a plateau, failing
to satisfy some of the
more demanding and
emerging applications
that often require min-
iature spectrometers or
microspectrometers in
a handheld or portable
format.
The remote-sensing community,
for example, pioneered the use of
hyperspectral imaging to correlate
objects in a heterogeneous field
of view (FOV) with their spectral
characteristics. To satisfy the needs of
this community, imaging spectrometers
were developed that used prisms and
prism-grating combinations (grisms).
This new generation of imaging
spectrometers has since been adapted
to address complex applications
including automated pathology,
biomedical imaging, and nanoparticle
imaging and characterization.1, 2
Imaging versus non-imaging
spectrometers
In the early 1900s it was observed that
all spectrometers took a point and im-
aged it as a line, at each wavelength, on
the detector. The image of a point on
the entrance slit was not only elongat-
ed due to astigmatism but also suffered
from curvature and other aberrations
(see Fig. 1). This not only made it impos-
sible to differentiate between the spectra
presented by two adjacent objects, but
also spread the light over a large area,
Because a prism transmits 90% of light
over an extended wavelength range,
matching it to a CCD detector with
close to 90% quantum effi ciency creates
a nearly ideal system that, with some
tradeoffs, can be miniaturized to meet
portable spectroscopy application needs.
FIGURE 1. A non-
imaging spectrometer
images a point as a
line (left); an imaging
spectrometer images
spatially separated
points as “points”
on the detector
(right). (Courtesy of
LightForm)
MINIATURIZED IMAGING SPECTROMETERS
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July 2010 www.laserfocusworld.com Laser Focus World 58
MINIATURIZED IMAGING SPECTROMETERS cont inued
reducing photon density and sensitivity.
A true imaging spectrometer images a
point in the FOV as a point on a detector
at each wavelength. With this capability
it is possible to reconstruct the spectral
characteristics of a heterogeneous FOV,
which satisfi es the imaging requirements
of most applications.
Grating-based imaging spectrometers
reduce astigmatism and other aberra-
tions by using aspheric optics or gratings
with asymmetrically distributed grooves
(ADG) produced holographically, or
with sophisticated ruling engines.3-6
The challenge is to produce a diffraction
grating that possesses the optimum focal
length, groove density, and wavelength
effi ciency, in a size that makes sense.
The quest for lighter, robust, more sen-
sitive spectrometers that operate over
extended wavelength ranges within the
remote Earth-sensing community has
resulted in the development of a new genera-
tion of prism-based, compact spectrometers.
Spectrometer basics
Whether a spectrometer uses a grating or
a prism, all wavelength-dispersive spec-
trometers image an entrance slit onto a
detector, at each wavelength. Unlike a
classical spectrometer, an imaging spec-
trometer dissects the image of the en-
trance slit along its length (perpendicu-
lar to the wavelength dispersion axis). In
use, an FOV is imaged onto the slit; then,
all objects appearing along the slit pres-
ent their spectra to the detector. To gener-
ate a spectral map, referred to as a hyper-
spectral image, the spectrometer is either
fl own over the FOV or the FOV is translat-
ed underneath the spectrometer on a con-
veyor belt or automated translation stage.
In both cases the spectrometer is used as
a spectrograph in which all wavelengths
are acquired simultaneously at each lo-
cation along the slit.
The ideal wavelength detector for an
imaging spectrometer is a CCD camera
where each row of pixels is assigned to
a location on the entrance slit. Each row
of pixels acquires a complete spectrum
from each location and the spectrum of
each point on the slit is dispersed across
a specifi c row of pixels. The spatial res-
olution is limited by the height of a row
of pixels and the spectral resolution
is determined by the properties of the
spectrometer, unless the CCD camera
is mismatched to the spectrometer. After
establishing the required spatial/spectral
resolution and wavelength range of the
application, the operating parameters
of the instrument can be calculated.7, 8
Spectral and spatial resolution
Given that the entrance slit is imaged
onto the detector bandpass, spectral
resolution (or bandpass BP) is defi ned
as BP = Sw
* Wd. Here, S
w = image of
the entrance slit (mm) and Wd = wave-
length dispersion (nm/mm). The aver-
age wavelength dispersion, Wd, is the re-
quired wavelength range divided by the
length of a row of pixels. If the appli-
cation characterizes a fi eld of nanopar-
ticles then the wavelength range needs
to stretch from 400 to 800 nm—a 400
nm spectral segment. And if each pixel
in the CCD detector is 4.65 × 4.65 μm
arrayed along rows 6.47 mm in length,
then the average Wd will be 400 divided
by 6.47 mm, or 62 nm/mm.
Assuming the application demands a
spectral resolution of better than 2 nm
(and for expediency it would be desir-
able to use is a standard 25 μm slit width),
then the system bandpass will be 0.025 ×
62, or 1.55 nm. Actual values of Wd and
Sw
vary with wavelength, so spectral reso-
lution will vary across the spectral range.
The image of the entrance slit will
present a full width at half maximum
(FWHM) of approximately 25 μm (Sw)
and will occupy an integer number of
pixels, with the number of pixels defi n-
ing the FWHM as 25/4.65 or 6.
Only three pixels are required to accu-
rately determine the peak wavelength
and the half maximum points; therefore,
there would be no loss in spectral reso-
lution and a gain in sensitivity if rows
of pixels were binned two by two. This
condition satisfi es the Raleigh criterion
for spectral resolution when the FWHM
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___________
CCD
Prism withcurved sides
Objects in a field of view
59Laser Focus World www.laserfocusworld.com July 2010
is that of the entrance slit when illumi-
nated by a monochromatic wavelength
such as a single-mode laser or a low-
pressure mercury discharge lamp. It is
worth emphasizing that spectral resolu-
tion depends on the width of the image
of the entrance slit, not the total number
of pixels on the CCD chip.
A spectrometer’s spatial resolution is
determined by the convolution of resid-
ual spectrometer aberration and the
height of a row of pixels. The net spa-
tial resolution is a quadratic where spa-
tial resolution equals the root of the sum
of the squares of residual system aberra-
tions, the size of a pixel, and any other
contributing factors.
A minimum of at least two pixels are
required to determine the location of an
object on the entrance slit; therefore, if the
FOV is imaged with a 40X microscope
objective the spatial resolution at the FOV
would be approximately 0.45 μm.
Correcting aberrations in a
prism-based spectrometer
Diffraction-grating spectrometers enable
aberration correction through modifi ed
groove distribution or the use of aspheric
focusing or collimating optics. The use
of aspheric optics with a prism is feasi-
ble, but unnecessary
if the prism itself can
be given “power” (see
Fig. 2). This special
power geometry used
optics with curved
sides, and was orig-
inally developed for
the SEBASS remote
hyperspectral imag-
ing system (www.lpi.
usra.edu/science/kirk
land/home.html) that
is fl own on aircraft
and operated in the far-infrared spec-
trum. A redesign for use in the wave-
length range from 365 to 920 nm resulted
in LightForm’s PARISS hyperspectral im-
aging system (www.pariss-hyperspectral-
imaging.com) for use mounted on any
microscope for biomedical, forensic, and
industrial spectral imaging.9
The optical system comprises a prism
with one side concave, the other con-
vex, and a spherical mirror for focus-
ing. The effective wavelength dispersion
is doubled because light passes through
the prism twice. Ray tracing is used to
determine the optimum curves of the
mirror and prism faces and the distances
between the mirror and prism.
Grating- versus prism-based
spectrometers
Diffraction-grating effi ciency varies con-
siderably with wavelength and peaks at the
blaze wavelength (see Fig. 3). If a grating
is non-blazed, such as many holographic
gratings, the peak effi ciency is lower but
can extend over a longer wavelength range.
In comparison a prism has a fl at 90%
transmission effi ciency over a very wide
wavelength range. This makes it feasi-
ble to use signifi cantly less expensive
cameras with lower quantum effi ciency
(QE). The majority of wavelength-sensi-
tive detectors (including photomultiplier
tubes, CCDs, and most silicon-based
detectors) have QE profi les that are very
similar to the effi ciency profi les of blazed
diffraction gratings.
For both a prism and a typical
diffraction grating, wavelength
dispersion is nonlinear. But because
the nonlinearity is greatest for a prism,
there is a surprising benefi t: Given that
spectral resolution and bandpass are
a function of wavelength dispersion,
a decrease in wavelength dispersion
FIGURE 2. An aberration-correcting prism spectrometer uses
optics with curved rather than fl at sides, somewhat like a lens
with a severe wedge. (Courtesy of LightForm)
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______________
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MILITARY•COTS•INDUSTRIALDC-DC CONVERTERS & POWER SUPPLIES
TRANSFORMERS & INDUCTORS
100
Wavelength (nm)
Efficiency (%)
80
60
40
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0800700600500400
Blazed grating
Prism
Camera QE
Non-blazedholo grating
300
Prism dispersionRelative camera QE
1.0
Wavelength (nm)
Relative wavelengthdispersion
0.8
0.6
0.4
0.2
0.0840 940740640
Diffraction grating dispersion
540440340
July 2010 www.laserfocusworld.com Laser Focus World 60
to longer wavelengths
results in a decrease
in spectral resolution.
Therefore, the spectral
resolution of prism
spectrometers is greatest
in the blue and lowest in
the red. However, light
throughput is directly
proportional to bandpass.
This is an advantage when
working with weakly
emitting samples because
as the QE of the camera
decreases, the light
throughput of a prism
increases as a function of
its bandpass (see Fig. 4).
Optimizing the size and
weight of any spectrome-
ters can be a juggling act
depending on the applica-
tion. When imaging spec-
trometers are used with a
telescope or microscope
to image an FOV onto
the entrance slit, it can be
a challenge to get enough
light through the system
with a slit width much
less than 25 μm. This
challenge, as well as the size of the CCD
chip and any linear dispersion in the sys-
tem, combines to defi ne the focal length
and groove density of the grating if this
is to be the wavelength-dispersive ele-
ment. The same is true for a prism sys-
tem except that only the focal length is
really negotiable.
Our PARISS prism-based imaging
spectrometer covers the entire spectral
range from 365–920 nm, is about 200
mm in length, and weighs approximately
2 kg—much of which is due to the
scientifi c CCD camera. A comparable
grating system is likely to be about
the same size and weigh up to 3 kg.
The high optical effi ciency, imaging
integrity, and immunity from diffraction
effects makes prism-based imaging
spectrometers a compelling addition to
the spectroscopist’s tool box.
REFERENCES
1. D.T. Dicker et al., Cancer Biology and Therapy 8,
1033–1038 (2006).
2. J. Aaron et al., Nano Letters 9, 10, 3612–3618 (2009).
3. M.P. Chrisp, “Aberration-Corrected Hologra-
phic gratings and their mountings,” in Applied
Optics and Optical Engineering, R.R. Shannon
and W.C. Wyant, Editors, Academic Press, Lon-
don, 391–451 (1987).
4. E. Loewen and E. Popov, Diffraction Gratings
and Applications, Marcel Dekker, New York,
NY (1997).
5. J. Reader, J. Opt. Soc. Am. 59, 1189–1196 (1969).
6. X. Prieto-Blanco et al., Opt. Exp. 14, 20, 9156–
9168 (2006).
7. J.M. Lerner, Cytometry 69A, 8, 712–734 (2006).
8. J. James and R. Sternberg, The Design of Optical
Spectrometers, Chapman & Hall, London (1969).
9. D. Warren et al., “Compact prism spectrographs
based on aplanatic principles,” Opt. Eng. 36,
1174–1182 (1997).
Jeremy Lerner is president of LightForm Inc.,
825C Merrimon Ave., Suite 351, Asheville, NC
28804; e-mail: [email protected]; www.
lightforminc.com.
MINIATURIZED IMAGING SPECTROMETERS cont inued
FIGURE 3. The effi ciency profi les are shown for blazed gratings,
non-blazed (holographic) gratings, and a prism, as well as
camera quantum effi ciency (QE). (Courtesy of LightForm)
FIGURE 4. The wavelength dispersion profi les of prism and
diffraction gratings are compared. Bandpass decreases with
wavelength dispersion. In the case of a prism the decrease
in bandpass compensates for the fall in QE of the camera,
resulting in an increase in sensitivity. (Courtesy of LightForm)
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___
61Laser Focus World www.laserfocusworld.com July 2010
JEFF HECHT, contributing editor
Shifting semiconductor laser wavelengths poses challenges
Nonlinear optics offer invaluable ways
to fi ll gaps in the laser spectrum, from
simple harmonic generation to more
complex optical parametric oscillators
(OPOs). Frequency doubling of diode-
pumped neodymium
(Nd) lasers has made
green laser pointers
cheap and compact,
but why can’t devel-
opers drop the diode
pumping and directly
double semiconductor laser output to
produce hard-to-fi nd wavelengths?
It’s been done for green light and
is already reaching the market in
pico-projectors from companies like
MicroVision (Redmond, WA).
But it’s not easy. Nonlinear wave-
length conversion requires not
only raw power but also high
beam quality and narrow-line
emission. It’s tough to combine all
those features in a semiconductor
laser. Yet progress is being made.
The fi rst products are on the mar-
ket, and developers are reporting
more encouraging results, includ-
ing new laser designs, diode pump-
ing of OPOs, and both harmonic
generation and difference-fre-
quency generation
with quantum cas-
cade lasers.
Quests for
doubled diodes
Serious work on di-
rect doubling of di-
odes started in the
early 1990s, when
diodes had reached high pow-
ers and the diode laser spectrum
stopped in the red. Doubling the
output of near-infrared diodes prom-
ised inexpensive sources for the short
end of the visible spectrum. It also
offered directly modulatable short-
wavelength lasers for applications
such as laser displays.
Coherent Inc. (Santa Clara, CA)
succeeded in developing a product
called the D3 (for direct-doubled-
diode) laser, which frequency dou-
bled the roughly 100 mW of an 860
nm diode to produce about 10 mW of
blue light at 430 nm.1 It required a dis-
tributed Bragg refl ector laser for nar-
row-line output, and the diode output
had to be mode-matched and phasel-
ocked into the external harmonic gen-
erator. It was a fi rst, but it found few
applications and eventually faded
away—no doubt partly because of
Shuji Nakamura’s remarkable success
in developing blue indium-gallium
nitride diode (InGaN) lasers at the
Nichia Chemical Corp. (Tokushima,
Japan). Coherent eventually devel-
oped optically pumped surface-emit-
ting semiconductor lasers, which are
frequency doubled to emit at visible
wavelengths but behave more like
solid-state lasers than diodes.
The success of blue diode lasers left
a gap in the green center of the vis-
ible spectrum, which emerged as a
problem a few years later as the con-
sumer electronics industry looked
for new technology for projection
television. Laser back-projection
promised a better color gamut than
fl at-panel displays, if a suitable laser
Nonlinear optics can generate new lines
from semiconductor lasers by harmonic
generation and frequency mixing, but
it requires high power, good beam
quality, and narrow linewidth.
FIGURE 1. Corning’s
green laser module for a
pico-projector is 4 mm
thick and shown sitting
on a smart phone for
scale. (Courtesy of
Corning Inc.)
P H O T O N I C F R O N T I E R S : FREQUENCY-SHIFTED DIODE LASERS
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Connecting minds for global solutionsThe premier optical sciences and technology meeting
Register Today
Conferences + Courses: 1-5 August 2010Exhibition: 3-5 August 2010
San Diego Convention CenterSan Diego, California, USA
spie.org/op
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LTA = 4 mm
WTA ≈ 425 μm
LRW = 2 mm
φTA = 6°
WRW = 4 μm
See us at Intersolar, Booth 8147
63Laser Focus World www.laserfocusworld.com July 2010
FREQUENCY-SHIFTED DIODE LASERS cont inued
source were available at about 530 nm.
Doubled Nd might have seemed a logi-
cal choice, but it couldn’t be directly
modulated at the required speed, so
developers turned to doubling 1060
nm diodes or other lasers to produce
530 nm green beams. Many of those
projects wound down as rear-projec-
tion television faded from the consumer
market, but a few shifted toward com-
pact pico-projectors for mobile devices,
where cost points are lower than for
televisions, says John Nightingale, an
optical consultant in Portola Valley, CA.
Corning Inc. (Corning, NY) is already
carving a niche out of the young pico-
projector market. Last year it intro-
duced a commercial version and is
supplying lasers to MicroVision for its
Showwx projector for iPods and laptops.
Corning’s green laser doubles the 1060
nm output of a distributed Bragg refl ec-
tor (DBR) laser emitting a single-spatial
mode and single frequency. The laser
includes three sections: one a DBR grat-
ing, a second for phase adjustment, and a
third for gain. Corning initially reported
generating up to 104.6 mW at the 530
nm second harmonic by coupling the
infrared DBR output into a periodically
poled lithium-niobate second-harmonic
generator.2 Measurements showed that
the green light could be modulated at
rates above 50 MHz as required for pro-
jectors, and later laboratory versions
reached green output of 184 mW.3
Corning’s fi rst commercial model,
introduced last year, emits 60 mW (see
Fig. 1). In May 2010 the company intro-
duced a prototype 80 mW version that
it says has wall-plug effi ciency of 8%
and can be modulated at speeds to 150
MHz as needed for extended graphics
resolution.
Tapered amplifi er lasers
Another approach to generating the
high-quality, high-power beam need-
ed for effi cient harmonic generation is
FIGURE 2. The tapered amplifi er developed at the Braun Institute includes a 2 mm length
of 4 μm ridge waveguide, with a 1 mm DBR at the back and a 1 mm gain section. The
remaining 4 mm amplifi er stage is tapered at 6°.4
One approach to generating
the high-quality, high-
power beam needed
for effi cient harmonic
generation is combining
a single-mode ridge
waveguide DBR laser with
a tapered amplifi er stage.
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__________
Micro-optical bench (MIOB)
Heater
Beam forming
DBR-taperedlaser
PPLN crystalλ/2
10 mm
488 nm output
M3 M4
L5 L1 L2 OD
L3L4
M2
PBS
HWP
M1PPLN
GRIN
BSD
GTA
5 mm
50 mm
July 2010 www.laserfocusworld.com Laser Focus World 64
FREQUENCY-SHIFTED DIODE LASERS cont inued
combining a single-mode
ridge waveguide DBR diode
laser with a tapered ampli-
fi er stage (see Fig. 2). Götz
Erbert’s group at the Fer-
dinand Braun Institute for
High-Frequency Technolo-
gy (Berlin, Germany) is in
the midst of a fi ve-year proj-
ect to develop compact sec-
ond harmonic sources with
output to a few watts in the
visible for a range of appli-
cations, from cinema-scale
projectors to precision spec-
troscopy. The group has
generated fundamental out-
put at 980 nm with 0.012
nm linewidth, power to 12
W, and a nearly diffraction
limited beam with vertical
divergence less than 15°.4
Single-pass second-harmon-
ic generation in periodically
poled lithium niobate gener-
ated more than 1 W at 488
nm. The group also is explor-
ing nonlinear techniques for
generating light from the ul-
traviolet to the infrared, and
together with Sina Riecke of
PicoQuant GmbH (Berlin,
Germany) has produced 30
ps pulses at 531 nm and megahertz rep-
etition rates.5
The Braun Institute group also is
working with the University of Potsdam
on a coupled ring resonator for harmonic
generation (see Fig. 3). The main ring
optically locks a tapered amplifi er laser
with the ring resonance, and couples the
fundamental output into a smaller ring
that contains a periodically poled lith-
ium niobate harmonic generator. Recent
experiments generated 310 mW of 488
nm output with 50 MHz linewidth at
18% optical conversion effi ciency.6
A joint project with Paul Michael
Petersen’s group at the Technical
University of Denmark (Roskilde,
Denmark) yielded fundamental output
of 1.38 W from a tunable diode between
659 and 675 nm with linewidth of 0.07
nm.7 The output is the highest from a
tunable diode in this range, and could
be doubled to the 335 nm range, shorter
than current ultraviolet diode lasers.
Combining the high-quality near-
infrared lasers with nonlinear optics also
can generate longer infrared wavelengths
where good sources are not available,
says Erbert. Together with the University
of Twente (Enschede, the Netherlands)
his group used 8.05 W at 1062 nm from
a monolithic diode amplifi er to pump a
singly resonant optical parametric oscil-
lator of periodically poled lithium nio-
bate. Tuning ranges were 1541 to 1600
nm for the signal wave and 3154 to 3415
nm for the idler. The idler power exceed-
ing 1.1 W at 3373 nm, the highest yet
FIGURE 3. Coupled ring resonators for diode-laser
harmonic generation developed by Potsdam-Braun
Institute Team feature a tapered amplifi er laser (TA) in the
top ring, along with a holographic diffraction grating (G),
an optical diode, a half-wave plate (HWP), a polarizing
beamsplitter (PBS), a beamsplitter (BS), and several
lenses. A periodically poled lithium niobate harmonic
generator (PPLN) is shared by the upper and lower ring.6
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______________________
65Laser Focus World www.laserfocusworld.com July 2010
from a diode-pumped OPO, and its
44% optical-to-optical conversion effi -
ciency made overall electrical to opti-
cal effi ciency 14.9%, about seven times
higher than from pumping an OPO with
a diode-pumped laser.8
Shifting quantum cascade
laser wavelengths
Nonlinear wavelength shifting is also
a hot topic for quantum cascade lasers,
where the major goals are second-har-
monic conversion, and difference-fre-
quency mixing to generate terahertz
frequencies.
The main interest in second harmonic
generation is to reach C-H, O-H, and
N-H stretching bands of hydrocar-
bons near 2.5–3.5 μm, which would
open important new applications, says
theorist Alexey Belyanin of Texas
A&M University (College Station, TX).
Problems with heterostructure growth
and current injection have hampered
development of quantum cascade lasers
with direct output at such short wave-
lengths. The fi rst observations of har-
monic generation in quantum cascade
lasers were made several years ago by
a collaboration involving Belyanin and
Frederico Capasso and Claire Gmachl,
then both at Bell Labs (Murray Hill,
NJ), but the power was limited to tens
of nanowatts.9 By 2004, they had raised
second harmonic power to milliwatt lev-
els at 4.45 μm.10 The harmonic genera-
tion occurs within the quantum cascade
structure itself. “Since we basically do
‘quantum engineering’ of the optical
nonlinearity, we can control it at our
will,” says Belyanin. That increases non-
linearity far above that of other materi-
als, and aids phase matching by shifting
electron resonances.11 He recently pro-
posed a way to generate second har-
monics as short as 1.5–2.5 μm and is
working with experimentalists to dem-
onstrate the idea.12
The appeal of difference-frequency
mixing for generating terahertz radiation is
the ability to operate at room temperature,
which for most applications is preferable
to the cryogenic cooling required for direct
terahertz emission from quantum cascade
lasers. The tradeoff, says Belyanin, is that
“there’s no free lunch because you lose a
lot of power.”
Difference-frequency generation
requires producing a quantum cascade
laser that operates at two separate wave-
lengths, which mix in the laser cavity
to generate the difference frequency.
“The terahertz output is modest, but it
is there,” says Mikhail Belkin of the
University of Texas at Austin (Austin,
TX), who mixed 7.6 and 8.7 μm wave-
lengths to generate the 60 μm difference
frequency while working with Capasso
at Harvard.13 “Theoretically we could
get milliwatts, but experimentally we
only get about 1 μW at room temper-
ature,” adds Belkin, who is continuing
this work in Austin. The good news is
that he sees plenty of opportunities to
raise the power further. Cryogenically
cooled terahertz quantum cascade lasers
can emit up to 150 mW but only at very
low temperatures, declining at higher
temperatures and to zero above 190 K.
Competition and outlook
Recent progress on green diode lasers
shows clear competition. At Photon-
ics West, Nakamura, now at the Uni-
versity of California at Santa Barbara
and Kaai (Santa Barbara, CA), an-
nounced a 523 nm green diode, and
Osram Opto Semiconductors (Regens-
berg, Germany) reported 50 mW out-
put in the laboratory from a 515 nm
InGaN laser.14 Yet Osram isn’t giving
up on doubling optically pumped sur-
face-emitting semiconductor lasers to
produce green light, and Corning is de-
livering products that are being built
into pico-projectors. Green diodes will
have to catch up in power and reliabil-
ity, and for all their appeal, there is no
guarantee they can beat doubled di-
odes—especially at the watt level. Oth-
er nonlinear wavelength shifting is on
the cutting edge of progress. Results
are encouraging, but we will have to
wait for the fi nal results.
REFERENCES
1. http://www.repairfaq.org/sam/laserdio.
htm#diocod
2. M.H. Hu et al., “High-power distributed
bragg refl ector lasers for green-light
generation,” Proc. SPIE 6116, 61160M,
doi:10.1117/12.647840 (2006).
3. J. Gollier et al., “P-233: Multimode DBR La-
ser Operation for Frequency Doubled Green
Lasers in Projection Displays,” Corning In-
corporated, Science and Technology, Cor-
ning, NY 14831, USA; available at http://
www.corning.com/WorkArea/downloadasset.
aspx?id=10533.
4. C. Feibig et al., “High-power DBR tapered
laser at 980 nm for single-path second-
harmonic generation,” IEEE J. Selected Topics
in Quant. Electron. 15, 978–983 (May–June
2009).
5. S.M. Riecke et al., “Pulse shape improvement
during amplifi cation and second-harmonic
generation of picosecond pulses at 531 nm,”
Opt. Lett. 35, 1500–1502 (May 15, 2010).
6. D. Skoczowsky et al., “Effi cient second-harmo-
nic generation using a semiconductor tapered
amplifi er in a coupled ring-resonator geometry,”
Opt. Lett. 35, 232–234 (Jan. 15, 2010).
7. M. Chi et al., “1.38 W tunable high-power
narrow-line external cavity tapered amplifi er
at 670 nm,” CLEO/QELS 2010, paper JTuD99.
8. A.F. Nieuwenhuis et al., “One-watt level mid-
IR output, singly resonant continuous-wa-
ve optical parametric oscillator pumped by a
monolithic diode laser,” Opt. Exp. 18, 11123
(May 24, 2010).
9. N. Owschimikow et al., “Resonant second-
order nonlinear optical processes in quantum
cascade lasers,” Phys. Rev. Lett. 90, 043902
(Jan. 31, 2003).
10. O. Malis et al., “Milliwatt second harmonic
generation in quantum cascade lasers with
modal phase matching,” Electron. Lett. 40
(Dec. 9, 2004).
11. M. Belkin et al., “Quasiphase matching of
second-harmonic generation in quantum
cascade lasers by Stark shift of electronic
resonances,” Appl. Phys. Lett. 88, 201108
(2006).
12. Y.-H. Cho and A. Belyanin, “Short-wavelength
infrared second harmonic generation in qu-
antum cascade lasers,” J. Appl. Phys. 107,
053116 (2010).
13. M. Belkin et al., “Terahertz quantum-cascade
laser source based on intracavity differen-
ce-frequency generation,” Nature Photon. 1,
288–292 (May 2007).
14. S. Lutgen, A. Avramescu, T. Lermer, M.
Schillgalies, D. Queren, J. Müller, D. Dini, A.
Breidenassel, U. Strauss, “Progress of blue
and green InGaN laser diodes,” invited talk at
Photonics West 2010, to be published in Proc.
SPIE 7616.
Tell us what you think about this article. Send an
e-mail to [email protected].
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______
___
________________________________
L A S E R S ■ O P T I C S ■ D E T E C T O R S ■ I M A G I N G ■ F I B E R O P T I C S ■ I N S T R U M E N T A T I O N
July 2010 www.laserfocusworld.com Laser Focus World 66
New productsWould you like to be included? Please send your
product description with high-resolution digital
image to: [email protected]
Semiconductor tapered amplifi ers
VAMP series semiconductor tapered amplifi ers are
designed to accept many fi ber-coupled seed sources for
easy alignment. The design includes output isolation,
over-current protection, and input seed monitoring in
every amplifi er, protecting the chip from self-lasing and
other hazardous conditions. It produces more than 1 W
of tunable signal frequency radiation.
New Focus
Santa Clara, CA
SM VCSEL
The new A4-PL model polarization-stabilized single-
mode VCSEL has an output of 1.4 mW, which is
double that of the previous model. The diode lasers
are available both on a chip and in a TO housing. The
emission wavelength is 855 nm ±10 nm. They can be
used in sensor technology.
Laser Components
Hudson, NH
Raman analyzer
The new ProRaman-L Series is designed for labora-
tory Raman analysis and method developments. It is
equipped with 532 or 785 nm excitation lasers and
provides solutions for semiconductor process control,
low concentration solution analysis, pharmaceuti-
cal process analyti-
cal technology, and
petrochemical
process control.
Enwave Optronics
Irvine, CA
info@enwaveopt.
com
Diode laser system
Power extensions for the
COMPACT Diode Laser
System Series include
300 W out of a 200 μm fi ber and 400 W out of a 300
μm fi ber at 9xx nm. The fi ber-coupled, turnkey diode
laser systems are based on conduction-cooled diode
laser bars. They are available with an industrial water-to-
air chiller, a power supply, and an integrated control unit.
In combination with a galvo scanner, they are suitable as
a source for quasi-simultaneous plastic welding.
DILAS Industrial Laser Systems
Mainz, Germany
www.dilas.ils.com
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nanoX® - Nanopositioning
www.piezojena.com
Piezo Positioner series nanoX®
Your provider fornanopositioning
■ Motion up to 800 �m
■ Unrivaled high stiffness
■ Sub-nm resolution
■ Unique bidirectional drive
incredibly precise
phone: +49 3641 66880fax: +49 3641 668866e-mail: [email protected]
phone: 508 634 6688fax: 508 634 6868e-mail: [email protected]
67Laser Focus World www.laserfocusworld.com July 2010
Line lasers
L3 LIMO Line Lasers are based on
process-optimized beam shapes and
allow the selection of an optimum
process window for scaling the system
to the industrial production level. With
a variety of processing heads, the
devices can be used for any type of
material. They can also be used for
annealing, crystallization, and temper-
ing of thin fi lms with high-speed linear
scanning processes and for rapid ther-
mal inspection and quality assurance.
LIMO
Dortmund, Germany
www.limo.de
Dual-CCD camera
The new ORCA-D2 is a dual-CCD
camera is designed around two ER-150
CCD devices. It can capture simulta-
neous dual-wavelength or multiple
focal-plane images. Each CCD captures
a 1280 × 960 pixel fi eld of view and
has independent exposure and gain
settings to accommodate signifi cantly
different intensity levels between the
two images as is often seen in FRET and
ratio imaging applications.
Hamamatsu
Bridgewater, NJ
Optical transceiver modules
SFP+ optical transceiver modules for
next-generation 10 Gbps Ethernet
equipment designs include the 10/1
Gbps dual-rate AFCT-701SDDZ
10GBase-Long Range (LR) single-mode
and AFBR-703SDDZ 10GBase-Short
New products
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New products
July 2010 www.laserfocusworld.com Laser Focus World 68
Range (SR) multimode fi ber transceivers.
Designed for use in enterprise and data
center applications, the dual-rate opera-
tion allows fl exibility in data rate control
through hardware or software control.
Avago Technologies
San Jose, CA
CCD cameras
The Clara CCD camera, based on mea-
sured QC data from the fi rst 200 cam-
eras built, has reduced typical read noise
to 2.4 electrons at 1 MHz. Cooling is
now offered to -55ºC with an internal
fan only (no water required), with -20ºC
under fan-off (vibration-free) opera-
tion. Features include a 1.3 Mpixel Sony
‘ICX285 sensor, low-noise 10 or 20 MHz
readout modes, and data channeled
through a USB 2.0 interface.
Andor
Belfast, Northern Ireland
www.andor.com/clara
Image analysis software
ImageUV microscope camera con-
trol and image analysis software is
designed for Windows 7. It features
quick resizing of windows, more visible
icons, and quick access to often used
documents and spectra with Jump
Lists. Windows Search gives engineers
and scientists a search engine to locate
and analyze data with the company’s
UV-visible-NIR microscopes.
CRAIC Technologies
San Dimas, CA
Strain sensors
The DT series of strain sensors allow
undercarriage structures and surfaces
to be more accurately monitored com-
pared to counting accelerometer meth-
ods. These rugged sensors incorporate
the technology of the fl ight-qualifi ed
DTD2684. Series DT3625 Sensors offer
a package of 0.45 × 0.25 × 0.14 in.
thick and weigh only 13 grams. They
are designed to monitor the fatigue
loading experienced by aircraft under
various conditions of fl ight speed,
weight, and mission confi guration.
Columbia Research Laboratories
Woodlyn, PA
Optical fi ber test platform
The Fiber Lab 800HE testing plat-
form targets applications where rough
handling and harsh conditions are
common, such as fi eld and laboratory
testing, manufacturing environments,
and military systems. The company is
also making the platform available for
customization with preconfi gured fl aws
in the fi ber to support CATV and tele-
com test equipment training.
M2 Optics
Holly Springs, NC
www.M2optics.com
Color smart camera
The BOA vision system, a highly inte-
grated smart camera, now has color
processing, which covers a broad range
of color inspection applications in the
automotive, food, packaging and phar-
maceutical industries, such as identi-
fi cation of parts or assembly features,
sorting, counting, and verifi cation of
color hue. Features include the iNSpect
Express software interface, 44 mm3
form factor, and IP67-rated housing.
DALSA
Waterloo, ON, Canada
www.dalsa.com
Prismatic multispecies
gas analyzer
The Prismatic Multi-Species Gas Analyzer
is a single analyzer that can measure
trace levels of as many as 16 different
molecules using continuous-wave cavity
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StarLab 2.00 software
1-866-755-5499
www.ophir-spiricon.com
Turn your PC into a laser power &
energy measurement work station
� 8 channels
� Math functions
� Data Logging
Made for Accuracy
Designed to measure
The True Measure of Laser PerformanceTM
The first concept of a programmable computer
was originated by Charles Babbage in England
in 1822 and serves mankind ever since.
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July 2010 www.laserfocusworld.com Laser Focus World 70
New products
ring-down spectroscopy (CW-CRDS).
It relies on a patented technique that
utilizes Brewster’s angle retrorefl ector
prisms to gain high refl ectivity over a
wide wavelength range.
Tiger Optics
Warrington, PA
www.tigeroptics.com
Bandpass fi lters
Bandpass interference fi lters are used
to selectively transmit a narrow range
of wavelengths while blocking others.
They are available as “traditional” coated
fi lters and high-performance “hard”
coated fi lters, which are fabricated via
an advanced plasma reactive sputter-
ing platform. Custom hard coated fi lters,
with optical densities greater than 6.0,
transmission greater than 90%, and edge
steepness less than 0.5%, can be rapidly
developed for OEM instrumentation.
Edmund Optics
Barrington, NJ
Optical components
for CV sensor system
Polymer optical components manu-
factured for the Closing Velocity (CV)
sensor system are known as “City
Safety.” The transmitter and receiver
unit of the system calculates the dis-
tance to objects and its approach speed
from signals in the range up to 10 m.
Jenoptik Business Unit
Triptis, Germany
www.jenoptik-los.com
High CRI, 0.5 W LED
The NWA-BSC is a high Color Rendering
Index (CRI) product in a 0.5 W white
version. Compliant to US Energy Star
guidelines, it fulfi lls the required mini-
mum CRI of 75. The LED has an oper-
ating current of 150 mA and achieves
typical 20 lm at a low thermal resistance.
The package dimensions are 3.5 × 3.5 ×
1.2 mm with a viewing angle of 120°.
Dominant Semiconductors
Melaka, Malaysia
www.dominant-semi.com
Collimating lenses
New aspheric molded lenses are designed
for collimating light from MWIR and
LWIR lasers, such as quantum cascade
lasers (QCLs). Manufactured from Black
Diamond chalcogenide glass, lenses have
a high NA for maximum light collection.
Antirefl ective coatings are available for the
SWIR (1.8–3 mm), MWIR (3–5 mm), and
the LWIR (7–12 mm) wavelength ranges.
Lightpath Technologies
Orlando, FL
www.lightpath.com
Nanopositioning stages
The new nano1x3 series x-y and x-y-z
nanopositioning stages are designed for
inverted microscopes from Leica, Nikon,
Olympus, and Zeiss. The low-profi le
design of 20 mm (0.8 in.) facilitates inte-
gration while a large aperture accom-
modates microscopy accessories such
as slide holders and Petri dish holders.
Other features include 200 μm x-y or
x-y-z travel and a 24 bit controller.
Physik Instrumente (PI)
Auburn, MA
Warm white LED
A warm white LED prototype is designed
for general illumination applications. It
provides a color temperature of 3000 K
and a color rendering index of 82. With
operating current of 350 mA and chip
surface of 1 mm2, the prototype of the
new single-chip LED achieves a bright-
ness of 124 lm, which corresponds to an
effi ciency of 104 lm/W.
Osram Opto Semiconductors
Sunnyvale, CA
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Manufacturers’ Product Showcase
71Laser Focus World www.laserfocusworld.com July 2010
IR Wavelength meters for Pulsed &
CW lasers covering from the UV to Mid-IR
When only the
most accurate
results matter,
TOPTICA delivers!
Our wavelength
meters are the
most accurate
with the best
resolution specs
commercially available. With the only high resolution
wavelength meter capable of reaching 2MHz!
All of our wavelength meters incorporate standard features:
• Models from 192-2250nm for broad coverage options
• Measurement speeds to 600Hz for the fastest results
• No moving parts ensuring greater stability
• Integrated calibration minimizing downtime
• PID control to drive your lasers
• Linewidth measurement offering greater capability
www.toptica.com
(585) 657-6663 • [email protected]
Conex™-MFACC Integrated
Linear Stage and Controller
This latest Newport innovation combines the popular MFACC
stainless steel linear stage with an inexpensive and compact
motion controller. This integrated confi guration allows easy
USB connection and simplifi es remote control of repetitive
tasks in optical setups. Conex, the superior performance of
Newport motion products, at affordable prices.
Newport Corporation
www.newport.com • (800) 222-6440
6100 Combo Laser Diode
and Temperature Controller
Newport’s new Model 6100 Combo Laser Diode and
Temperature Controller is equipped with an impressive
software suite that will allow you to make serious
measurements in a matter of minutes. The suite consists of
a high speed LIV characterization and a temperature tuning
software for TEC with a full PID parameter control. For the
LIV characterization, also consider using Newport’s optical
power meters such as the 1936-C.
(Newport logo)
Newport Corporation
www.newport.com • (800) 222-6440
A New Way to Accurately Measure Color
TRICOR Systems Model 600 Non-Contact Imaging
Spectrophotometer will allow the user to capture image data
from any scene and provide CIE Chromaticity Coordinates
of each pixel located in that scene. Quantify spectral
transmittance, refl ectance and output from illumination and
or display systems. The Model 600 can be used to measure
radiated sources, refl ectance as well as transmittance from
380nm to 780nm. This spectral information can be used to
calculate various color coordinates of refl ectance colors
under various types of illuminants. Color units include: XYZ,
xyz, L*a*b*, Lab, u’v’, L*u*v* and CCT.
1650 Todd Farm Dr., Elgin, IL 60123 • 847-742-5542
www.tricor-systems.com • [email protected]
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July 2010 www.laserfocusworld.com Laser Focus World 72
Manufacturers’ Product Showcase
One-year subscription to LASER FOCUS WORLD FREE!
Visit us online at www.lfw-subscribe.com
or call Customer Service at 847.559.7500
New USB Control Interface
FEMTO Messtechnik GmbH just introduced the new USB
Control Interface LUCI-10 for the remote control of FEMTO
amplifi ers and
photoreceivers
directly from a
PC. The interface
supports opto-
isolation of the
PC USB port
from the signal
path of the
connected amplifi er module to guarantee signal integrity
and low noise performance. The LUCI-10 electronics is fully
integrated inside the D-Sub hood and bus-powered through
the USB port. It comes with an extensive software package
containing the necessary DLL driver and software examples
like Graphic User Interfaces (GUI’s), sample VI’s and a
FEMTO Library to help generate your own control software
in a LabVIEW™ environment.
FEMTO Messtechnik GmbH
Paul-Lincke-Ufer 34, 10999 Berlin, Germany
(p) +(49) 30-446 93 86, (f) +(49) 30-446 93 88
e-mail: [email protected], http://www.femto.de
NEW! Fiber Laser Focusing Lenses
from OPTOSIGMA Corp.
• High performance Multi-Element lenses, suitable for
focusing and collimating solid state lasers such as Yb
Fiber laser, YAG laser and YV04 laser
• Optimized AR coating from 1040nm – 1150nm; maintaining
Transmittance at 633nm for HeNe pointing lasers
• Corrected for spherical aberration and coma @1064 nm.
Lens is diffraction limited for f# >2 (NA < 0.25)
• Lens optimized to reduce the effect of thermal expansion
by using all fused silica elements
www.optosigma.com
OPTIMIZED TO REDUCE THERMAL LENSING
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______________
73Laser Focus World www.laserfocusworld.com July 2010
Cargille Laboratories
Cargille Labs, started in 1924,
develops and manufactures
Optical Liquids calibrated
for Refractive Index for use
throughout many laboratory
disciplines involving microscopy
and/or optics, ex: aerospace,
telecommunications, particle
identifi cation, hematology,
geology, testing labs, art
conservation, etc. A Specialty
Optical liquids catalog is available
which includes typical optical & physical properties and
comparative diagrams of glasses and optical liquids.
Cargille’s other catalog includes data sheets on Disposable
Beakers, Heavy Liquids, Immersion Oils, Refractive Index
and Immersion Liquids, Plastic Boxes, Reference Sets,
Sample Storage Systems, Micro Slide and Tissue File
Boxes and Viscosity Tubes.
Cargille Laboratories
55 Commerce Road, Cedar Grove, NJ 07009 USA
Tel.: (973) 239-6633, Fax: (973) 239-6096
E-mail: [email protected], www.Cargille.com
FemtoFiber pro — versatile Erbium
doped ultrafast fi ber laser
TOPTICA’s new FemtoFiber
pro is an ultrafast laser featuring
high peak powers along with
completely hands-off operation
while offering excellent
performance. With a focus
on reliability and robustness,
new technologies have found
their way into the professional
graded product, including the
saturable absorber mirror (SAM)
and the use of only polarization
maintaining (PM) fi bers. The
device ensures self-starting
and stable mode-locking under all laboratory conditions.
The FemtoFiber pro is available with fundamental output
at 1560nm with a pulse width well below 100fs (FemtoFiber
pro IR) and also with second harmonic output at 780nm
(FemtoFiber pro NIR).
www.toptica.com
(585) 657-6663 • [email protected]
New Thermal Laser Power Sensors
For powers up to 400W
these high performance,
heat dissipation sensors
feature an array of pins
for cooling, unlike other
devices which rely on fl at
cooling fi ns that consume
signifi cantly more space.
As a result, they are the
most compact laser power
sensors on the market, half
the size of most devices.
www.ophiropt.com/laser-measurement
(866) 755-5499
Passive Q-Switched 1064 nm DPSS Laser
3 mJ, 1MW peak output
This very compact high-energy laser delivers 3 mJ pulses
with pulse durations of 3 ns. The side-pumped, self-aligning
monolithic design allows for high peak powers in a compact
size while providing stable and maintenance-free operation.
321 South Main Street, Suite 102,
Providence, RI 02903 USA
Tel.: (401) 274-4700, [email protected]
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July 2010 www.laserfocusworld.com Laser Focus World 74
Business Resource Center
Used Equipment
Laboratory EquipmentUsed and Refurbished
Lasers, microscopes, mounts, motorized
and manual stages, vibration tables,
clean room equipment and more!
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www.photomachining.com/inventory/
603-882-9944
Laser Modules VCSEL / Transceivers
Lasermate Group, Inc. provides high quality and low cost of• 266nm–1625nm lasers including UV, blue, green,
red, & infrared laser diodes, modules & products.• 670nm–850 nm VCSEL chip, array, diode, transmitter
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InGaAs PIN Photodiode• Up to 10Gbps GaAs & InGaAs PIN photodiodes & arrays• 100M to 10G optical transceivers including 1×9, SFF,
SFP & GBIC with duplex & simplex connectors• 1W to 3W blue, green, red, yellow & white LED
modules• Laser safety goggles and laser accessories• Fiber Optic DVI Extender & HDMI Extender • Fiber Optic Test Tools including fi ber checker, fi ber
meter, fi ber optic light source
Call: (909) 623-4995 Fax: (909) 623-4915E-mail: [email protected]
www.lasermate.com
Optics / Polarizers Manufacturing
INFRARED OPTICSwindows • prisms • lenses • filters
AgBr CdTe KCI Sapphire
AgCl Csl KRS-5 Si
AMTIR GaAs LiF SiO2
BaF2 Ge MgF2 ZnS
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CO2 LASER OPTICSlenses • mirrors • beamsplitters
reflectors • output couplers
POLARIZERSwire grid • free-standing • far IR
FIBER OPTICSUV-mid IR single or bundled assemblies
UV SiO2 • GeO • Sapphire • ZrFChalcogenide • Silver Halide
COATINGSanti-reflection • hard carbon
infrared • metalization
REFLEX Analytical Corporation“Serving you across the Spectrum”
PO Box 119 Ridgewood, New Jersey 07451Internet: www.reflexusa.com
E-mail: [email protected]: 201-444-8958 Fax: 201-670-6737
Request our FREE catalog
Used Equipment
ON A BUDGET? NEED EQUIPMENT?
Visit www.lasersurplus.com and discover hundreds of quality new and used items at a fraction of the original cost. All kinds of optical related items are listed with photos and prices.
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(214) 631-LASE (5273)www.lasersurplus.com
WANTEDUsed & Surplus Laser Equipment
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New and used lasers including:
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Midwest Laser Products, LLCP.O. Box 262, Frankfort, IL 60423
Ph. (815) 462-9500 FAX (815) 462-8955
Web: http://www.midwest-laser.com
email: [email protected]
Optics / Coatings Manufacturing
WAVEPLATES ON DEMANDOptiSource has made a personal commitment
to deliver value to our customers.
Value equals price plus convenience plus reliability.
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ADVERTISING SALES OFFICES
Advertiser&web index
75Laser Focus World www.laserfocusworld.com July 2010
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Amplifi cation Technologies ....................... 22
Apollo Instruments Inc. ............................. 34
Argyle International Inc. .............................37
Avantes BV ................................................. 59
B&W TEK .................................................... 58
BioPhotonic Solutions Inc. .........................18
Bristol Instruments .....................................10
BWT Beijing Ltd. ........................................ 36
Cambridge Technology ................................ 6
Cargille Laboratories ................................. 73
Castech Inc. ............................................... 38
Chunghwa Telecom Laboratories ............. 72
Coherent Inc. ............................................. 30
Continuum ................................................. 23
CVI Melles Griot ......................................... 29
Dilas Inc. .................................................... 25
Edmund Optics ........................................... 11
Electro Optical Products Corp. ............ 52, 54
Electro-Optics Technology ........................ 20
FEMTO Messtechnik GmbH ....................... 72
Fermionics Opto Technology ......................21
G-S Plastic Optics ...................................... 64
GSI Group Inc. .............................................47
Hellma USA .......................................... 24, 63
Laser Institute of America ......................... 44
Lee Laser Inc. .............................................14
Lightmachinery Inc. ..............................15, 37
Master Bond ...............................................67
Micro Laser Systems Inc. .......................... 34
Mightex Systems ....................................... 49
Nanoplus GmbH ......................................... 40
Newport Corp. ............ C2, 28, 43, 46, 71, C4
NM Laser Products Inc. ..............................24
Oclaro ..........................................................27
Ophir-Spiricon Inc. ......................... 19, 69, 73
Optical Building Blocks Corp. .................... C3
Optical Research Associates..................... 42
OptoSigma Corp................................... 12, 72
OSI Optoelectronics ....................................41
Photon Inc. ................................................. 53
PI (Physik Instrumente) L.P. ...................... 55
Pico Electronics ......................................... 60
Piezosystem Jena GmbH ............................67
Power Technology ........................................1
Precision Photonics ................................... 50
Qioptiq Imaging Solutions ........................... 8
RPMC ......................................................... 26
Spectra Systems ....................................... 73
SPIE Optics + Photonics ............................ 62
Stanford Research Systems ..................... 45
StockerYale Inc. ......................................... 43
Thermo Fisher Scientifi c ............................17
Thin Film Center Inc. .................................. 34
Toptica Photonics ................................. 71, 73
Tricor Systems ............................................71
Trumpf ...........................................................4
VLOC ............................................................16
Vuemetrix ....................................................21
Xi’an Focuslight Technologies Co., Ltd. .... 35
Zemax Development Corp. ........................ 32
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July 2010 www.laserfocusworld.com Laser Focus World 76
IN MY
VIEWB Y J E F F R E Y B A I R S T O W
Jeffrey Bairstow
Contributing Editor
The sayings of Rear Admiral Grace Murray Hopper, USNScanning the “New Arrivals”
shelf of my local library recently, I was
very pleasantly surprised to come across
an intriguing new book by Professor Kurt
Beyer: Grace Hopper and the Inven-
tion of the Information Age [MIT Press,
Cambridge, MA (2009)]. I fi rst met the
then-Commander Grace Hopper, USN,
in Seattle where she gave the keynote
address at the History of Programming
Languages conference in June of 1978.
As I recollect, the meeting was standing-
room only, particularly in the sessions
where Grace Hopper participated.
The conference attendees frequently
referred to Grace Hopper as “Amazing
Grace.” Indeed, the numerous achieve-
ments of Grace Hopper in computer pro-
gramming were nothing short of amazing.
She had an outstanding career that encom-
passed military research and development,
academic research and teaching, and busi-
ness software design and development.
Professor Beyer has written quite an
interesting biography of this leading pio-
neer in computers and programming. He
details Hopper’s World War II assignment
by the US Navy to the Harvard University
Computation Laboratory, the home of the
huge Mark 1 electromechanical calcula-
tor. At the end of the war, Hopper joined
Remington Rand, a typewriter company
that was developing computers for poten-
tial business use (the Univac series).
Despite the extensive male chauvin-
ism of that time, Hopper had unparalleled
opportunities to develop her own ideas
on computer programming. She also
honed her research and teaching skills.
Grace Hopper may not have been the
inventor of the Information Age, but she
certainly was a moving force in the rapid
development of computers and program-
ming languages for business applications.
Whenever Hopper “retired,” new
assignments were speedily offered and
were welcomed by Amazing Grace. She
was offi cially retired from the US Navy
in 1986 as the service’s oldest serv-
ing offi cer. She was promptly hired by
Digital Equipment Corporation, where
she worked until her death in 1992 at
the age of 86.
You’ll have to read the book to get
the full fl avor of the radical ideas and
machine-gun delivery of Grace Murray
Hopper. However, I thought I might
give you some of the observations that
poured forth from this diminutive Navy
person who always appeared in public in
her full dress Navy uniform.
(N.b. Grace Hopper’s original observa-
tions are in italics; the comments imme-
diately following each one are mine.)
On computing
Information is more valuable than the
hardware which processes it.
A situation that becomes even more
obvious as desktop and laptop comput-
ers become ever more ubiquitous.
Management versus leadership
You cannot manage men into battle.
You manage things; you lead people.
Both military forces and business
enterprises need strong leaders in
order to survive.
Getting things done
It is much easier to apologize
than it is to get permission.
Just as saying “No!” is much easier than
saying “Yes!” How often do we take the
easy route rather than the harder and
often riskier one?
Taking risks
A ship in port is safe but that is
not what ships are built for.
Spoken like the high-ranking naval
offi cer she was!
Pushing the envelope
At any moment there is always a line
representing what your boss will believe.
Go as close to that line as possible.
Defi nitely words to live your business
life by!
If you’d like to hear more wisdom
from Grace Hopper, try YouTube (www.
youtube.com), where you can fi nd sev-
eral videos featuring her. Look for a very
entertaining interview by Dave Letterman.Grace Hopper may not have
been the inventor of the
Information Age, but she
certainly was a moving force
in the rapid development of
computers and programming
languages.
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