Tentative Schedule: # Date Text Topics1 Jan 6 (Mo) LEO Ch12.1-12.4, Class Lecture Tunable Lasers, Organic Dye Lasers 2 Jan 8 (We)

LEO Ch12.1-12.4, Class Lecture Tunable Solid State Lasers, Alexandrite & Ti-Sapph.

Lasers, TM:II-VI Lasers(Class Lecture) Homework 1, Due January 22, 2012

3 Jan 13 (Mo) LEO Ch12.1-12.4, Class Lecture Tunable Solid State Lasers, Alexandrite & Ti-Sapph. Lasers, TM:II-VI Lasers(Class Lecture)

4 Jan 15 (Th)

Class Lecture Color Center Lasers

Jan 20 (Mo) MLK Holiday No classes 5 Jan 22 (We) Exam 1 - Grades Exam 1 over chapter 12 – Correct Solution 6 Jan 27 (Mo) Ch 13.1-13.7 and class lecture Semiconductor Lasers, Semiconductor Physics

Background 7 Jan 29 (We) Ch 13.1-13.7 and class lecture Semiconductor Lasers, Semiconductor Physics

Background, Homework 2, Due February 5, 20128 Feb 3 (Mo) (Ch.13.8-13.15) Semiconductor Lasers 9 Feb 5 (We) (Class Lecture, Ch.14) Ray Tracing in an Optical System

Homework 3, Due March 3, 2012 10 Feb 10 (Mo) (Class Lecture, Ch.14) Semiconductor problem solving

Ray Tracing in an Optical System 11 Feb 12 (We) (Class Lecture or Ch.16.1-16.7) Gaussian Beams 12 Feb 17 (Mo) (Class Lecture or Ch.16.1-16.7) Gaussian Beams 13 Feb 19 (We) (Class Lecture or Ch.15 and

Ch.16.8-16.14) Optical Cavities

14 Feb 24 (Mo) (Class Lecture or Ch.15 and Ch.16.8-16.14)

Optical Cavities; Three and four Mirror Focused Cavities

15 Feb 28 (We) (Ch.16.8-16.14) Optical Cavities; Cavities for Producing Spectral Narrowing of Laser Output Sample Problems for Test2

16 Mar 3 (Mo) Exam 2 Grades Exam 2 over chapters 13-16 Correct Solutions 17 Mar 5 (We) (LEO Ch. 18) Optics of Anisotropic Media 18 Mar 10 (Mo) (LEO Ch. 18) Optics of Anisotropic Media Homework #4 problems

18.2; 18.3; 18.4; 18.5 ch.18 LEO Due March 17. 19 Mar 12 (We) (LEO Ch. 20, 21) Wave Propagation in Nonlinear Media 20 Mar 17 (Mo) (LEO Ch. 21) 2nd Harm. Generation. Up and Down-Conversion, Optical

Parametr. Amplification; Homework # 5 due March 31 21 Mar 19 (We) (LEO Ch. 21) 2nd Harm. Generation. Up and Down-Conversion, Optical

Parametr. Amplification Mar 24(Mo) Spring Break No classes Mar 26 (We) Spring Break No classes 22 Mar 31 (Mo) (LEO Ch. 19, 21) The Electro-Optics and Acousto-Optic Effects and

Modulaton of Light Beams Homework #6 due April 9 23 April 2 (We) (LEO Ch. 19, 21) The Electro-Optics and Acousto-Optic Effects and

Modulaton of Light Beams Homework #5 review 24 April 7 (Mo) (LEO Ch.22.1-22.8) Detection of Optical Radiation 25 April 9 (We) (LEO Ch.22.6-22.8) Noise in Photodetectors Homework #7 due April 16 26 April 14 (Mo) (LEO Ch.22.6-22.8) Photodiode Arrays and CCDs; Sample problems for test 3 27 April 16 (We) Exam 3 Grades Exam 3 over chapters 18-22 Correct Solutions28 April 21 (Mo) Review for Final Review for Final 29 April 23 (We) FINAL GRADES FINAL EXAM Over Chapters 12-22 and class notes

4:15-6:45pm CH 394

2

Laser Physics II

PH482/582-VT (Mirov)

Tunable Solid State Lasers

Lecture 2-3

Spring 2014C. Davis, “Lasers and Electro-optics”

3

Broadband media overview• Natural definition of bandwidth is • Natural definition of bandwidth is

4

Alexandrite Lasers

5

6

7

8

9

Ti-Sapphire Lasers

10

11

Coordinate system frequently used relates to the plane made by the propagation direction and a vector perpendicular to the plane of a reflecting surface. This is known as the plane of incidence.

The component of the electric field parallel to this plane is termed p-like (parallel) and the component perpendicular to this plane is termed s-like (from senkrecht, German for perpendicular).

Polarized light with its electric field along the plane of incidence is thus denoted p-polarized, while light whose electric field is normal to the plane of incidence is called s-polarized.

p polarization is commonly referred to as transverse-magnetic (TM), and has also been termed pi-polarized or tangential plane polarized.

s polarized light is also called transverse-electric (TE), as well as sigma-polarized or sagittal plane polarized.

Explanation of sigma and pi polarization

12

13

14

Chromium doped LiSAF and LiCAF Lasers

15

16

Room Temperature Middle Infrared lasers based on Transition Metal

(TM: Cr2+, Fe2+, Co2+, Ni2+ doped II-VI (ZnS, ZnSe, ZnTe, CdS, CdSe)

semiconductor crystals

17

OUTLINEI. Motivation Why TM2+: II-VI? Why Cr2+ and Fe2+?

II. Overview of Cr and Fe-doped II-VI lasers State-of-the-art Cr: ZnS and ZnSe Sample preparation

III. New regimes of excitation and lasing Microchip cw and gain-switched lasing Multi-line or ultrabroadband lasing in spatially dispersive cavities Lasing via photoionization transitions Mid-IR Cr:Al:ZnSe electroluminescence

IV. Fe2+:ZnSe spectroscopic characterization

V. RT Fe2+:ZnSe gain switched lasing over 3.9-4.8m spectral range

VI. Conclusions and Future Outlook

18

Why broadband laser media?Ultra-short pulses

– time-resolved measurements – chemical reaction control – XUV generation – frequency standards

Ultra-broad spectra– optical coherence tomography – spectral slicing– intracavity absorption

Broadly tunable narrowband sources– optical coherence tomography– spectroscopy– cavity ring-down measurements– photoacoustic measurements

19

Interest for infrared wavelengthsFor femto-chemistry, molecular time-resolved measurements, molecular spectroscopy, trace gas analysis, biomedical applications, etc. one should directly reach molecular fingerprint 2-20 m region.

Mid-IR tunable, cw-fs sources are required

Requirements:• Sufficient bandwidth• Low cost, compact, directly diode-pumped low threshold• High brightness, i.e. good spatial coherence (TEM00).

Solutions:• OPO (bulk ZGP, PPLN, orientation-patterned GaAs): almost ideal solutions, but rather

complex and costly• QCL: nice solution for λ > 3.4 µm, not as broadband• Semiconductor InGaAsSb/GaSb lasers: narrow tuning, no fs, gap around 2.7-3 µm• Crystalline vibronic lasers: ultrabroadband up to 45 % λ, cw-fs, room-temperature

0.2 0.5 1 2 5 10 20 µm

Athmospheric transmission

Ti:S/Cr:LiSAF

Molecular frequenciesCr:YAG

Cr:Zn/CdSe

Tm:laser

Fe:ZnSeCo:MgF2

20

Three different semiconductor technologies for direct lasing in Mid-IR

a) A diode laser generates light from the recombination of electrons and holes across the semiconductor’s bandgap, and the material’s bandgap determines the wavelength of emission.

b) In a quantum cascade laser, light is generated from an energy transition in the conduction band of a semiconductor superlattice. By changing the thicknesses of the quantum wells and barriers in the superlattice, we can change the wavelength of light emitted.

c) In transition metal doped II-VI semiconductors light is generated from an energy transition of Impurity excited optically or electrically. Impurity emission bandwidth determines the wavelengthof emission.

c

e e

h h

Cr2+ZnSe

n:ZnSe

p:ZnSe

21

MOTIVATION for TM:II-VI

Crystalline vibronic lasers – viable solutionActive interest in TM doped II-VI compounds is explained by the fact thatthese media are close mid-IR analogues of the titanium-doped sapphire(Ti-S) in terms of spectroscopic and laser characteristics and it isanticipated that TM2+ doped chalcogenides will lase in the mid-IR with agreat variety of possible regimes of oscillation, similar to the Ti-S laser.

Significant advantages: TM2+ doped II-VI materials can be directly pumpable with radiation of

fiber lasers and/or InGaAsP/InP diodes or diode arrays. In comparison with Ti-S they feature higher maximum permissible dopant

concentration, higher cross sections and in result microchip lasingarrangements are feasible.

Due to effective thermo-diffusion of TM in II-VI, diffusion doping ofstarting material is feasible.

Have potential for direct electrical excitation (doped QD or QW lasers).

For molecular spectroscopy, trace gas analysis, biomedical applications, etc. one should directly reach molecular fingerprint 2-20 m region. Mid-IR tunable, cw-fs sources are required.

22

Why II-VI are so special for Mid-IR lasing?

Host Phonon cut-off

ZnTe 210 cm-1

ZnSe 250 cm-1

ZnS 350 cm-1

YAG 850 cm-1

YLF 560 cm-1

The heavy anions of II-VI crystals ensure that the optical phonon cutoff occurs at very low energy, thus maximizing the prospects for radiative decay of mid-IR luminescence in these crystals.

23

Why Cr2+ & Fe2+? Calculated Multiplet Structure for 3d impurities in ZnSe (after A Fazzio, et al., Phys. Rev. B, 30, 3430 (1984)

First excited levels lie at the right energy to generate 2-3 (Cr) & 3.5-5 m (Fe) mid-IR emission.

The ground and and first excited levels have the same spin, and therefore will have a relatively high cross-section of emission.

Higher lying levels have spins that are lower than the ground and first excited levels, greatly mitigating the potential for significant excited state absorption at the pump or laser transition wavelengths.

The orbital characteristics of the ground and first excited levels are different, and will experience a significant Franck-Condon shift between absorption and emission, resulting in broadband “dye-like” absorption and emission characteristics, suitable for a broadly tunable laser.

24

The top two: Cr:ZnSe and Cr:ZnS

1400 1600 1800 2000 2200 2400 2600 2800 30000

5

10

15

Tm:Y

ALO

Tm:Y

AG

(1

0-19 c

m2 )Er

:fibe

rIn

GaA

sP d

iode

s

Co:MgF2

Gain

Absorption

Wavelength, nm

Cr:ZnS

1400 1600 1800 2000 2200 2400 2600 2800 30000

5

10

15

Tm:Y

ALO

Tm:Y

AG

(1

0-19 c

m2 )Er

:fibe

rIn

GaA

sP d

iode

s

Co:MgF2

Gain

Absorption

Wavelength, nm

Cr:ZnSe

I.T. Sorokina, E. Sorokin, S. Mirov, V. Fedorov, V. Badikov, V. Panyutin, K. Schaffers, Opt. Lett., 27, 1042 (2002).

The only two types so far to allow tunable CW (also diode-pumped!) operation *).ZnS ZnSe

Lattice constant 5.4 Å 5.67 Å

Crystal structure mixed-polytype cubic

Bandgap 3.8 eV 2.8 eV

Hardness (Knoop) 160 120

Thermal conductivity

27 W/mK (cubic)

17 W/mK (hex)18 W/mK

dn/dT (10-6 K-1) 46 70

Transparency 0.4–14 µm 0.5–20 µm

Refractive index 2.27 2.45

Emission peak 2350 nm 2450 nm

Absorption peak 1680 nm 1780 nm

Lifetime (300 K) 5 µs 4 µs

Slope efficiency 53 % 71 %

Crystal Laser Characteristic Output parameter ReferenceCr:ZnSe CW, output power, W 13 I. Moskalev, V. Fedorov, S. Mirov, P. Berry, K. Schepler, ASSP’09

CW, Tuning Range, nm 2000‐3100 I.Sorokina, Solid State Mid‐Infrared Laser Sources, vol. 89, 2004.

CW, efficiency, % 60‐70 G.J.Wagner, et al., Opt. Lett., 24, 19‐21 (1999).

CW, microchip, output power, W 3 I. Moskalev, V. Fedorov, S. Mirov, Optics Express 16, 4145 (2008)

CW, Hot‐Pressed Ceramic Laser, W 0.25 I. Moskalev, V. Fedorov, S. Mirov, Optics Express 16, 4145 (2008)

CW, Single Frequency, oscillation linewidth, MHz

20 @ 10 mW<120 @ 150 mW

G.J.Wagner, et al., ASSP 2004, WB12.I.Moskalev, et al., 6552‐36, Laser Source Technology…III

CW, Multiline operation 40 lines over 2.4‐2.6 m I. Moskalev, S. Mirov, V. Fedorov, Optics Express 12, 4986 (2004).

Pulsed, Output power, W 18.5 @ 10KHz T.J.Carrig, et al., Proceedings of SPIE Vol. 5460, 74‐82 ( 2004).

Pulsed, Output Energy, mJ 14 @ 200s P.Koranda, et al., Optical Materials, in press (2007).

Pulsed, Tuning range, nm 1880‐3100 U.Demirbas, A. Sennaroglu, Opt. Lett., 31, 2293‐2295 (2006).

Pulsed Microchip, Energy, mJ 1 S.B.Mirov, et al., CLEO 2002, pp.120‐121.

Gain‐switched, Hot‐Pressed Ceramic Laser, Energy, mJ

2 @ 5 ns A. Gallian, V. Fedorov, S.Mirov, et al., Opt. Expr. 14, 11694 (2006).

Mode‐locked, duration, fs 80 @ 80 mW I.Sorokina, E.Sorokin, ASSP 2007, WA7. “

Cr:ZnS CW, output power, W 10 I.Moskalev, V.Fedorov, S.Mirov, et al., Photonics West 2009.

CW, Tuning Range, nm 1940‐2840 I.Sorokina, E.Sorokin, S.Mirov, et al., Opt. Lett., 27, 1040 (2002).

CW, efficiency 53% S.B.Mirov, et al., Optics Letters, 27, 909‐911, (2002).

CW, microchip, output power, W 0.1 S.B.Mirov, et al., Optics Letters, 27, 909‐911, (2002).

Gain‐switched Microchip, Energy, mJ 0.5 S.B.Mirov, et al., CLEO 2002, pp.120‐121.

Mode‐locked, duration, fs 1100 @ 125 mW I.T.Sorokina, E.Sorokin, T.J.Carrig, K.I.Schaffers, ASSP 2006,TuA4.

Fe:ZnSe Pulsed @150K, energy, J 5 J. J. Adams, et al., Opt. Lett., 24, 1720‐1722 (1999).

Pulsed@85K, energy, mJ 187 A. A. Voronov, et al., ” Quantum Electron., 35(9), 809‐812 (2005).

Pulsed, efficiency,% 43 A. A. Voronov, et al.,” Quantum Electron., 35(9), 809‐812 (2005).

Microchip gain‐sw. @300K, energy, J 1 @ 5ns J.Kernal, et al., Optics Express, 13, n 26, 10608‐10615 (2005).

Gain‐switched @300K, energy, mJ 0.4 @60 ns V.A. Akimov, et al., Quantum Electronics 36, 299‐301 (2006).

Gain‐switched @300K, tun. range,nm 3950‐5050 V.V. Fedorov, S.B. Mirov, et al., IEEE J. of QE 42, 907‐917 (2006).

Mid-nineties: Zn-chalcogenide lasers,( Livermore Group L. DeLoach, R. Page et al 1996)Cd-chalcogenide lasers, ( K. Schepler et al (Cr:CdSe), and S. B. Trivedi et al (Cr:CdTe and compounds) 1997)

Best results Cr:ZnSe, Cr:ZnS, Fe:ZnSe

26

Fabrication methods and problems to be resolved Bridgman technique (sublimation of chemicals requires simultaneous use

of high temperature and pressure, (1550C & 75 atm. – economically not viable)

Chemical vapor transport (CVT) (doping is very difficult)

Physical vapor transport methods (PVT) (doping is very difficult)

Pulse laser deposition Hot-pressed ceramics The post-growth thermally diffusion doping by Cr or Fe

All these methods have problems requiring additional studiesKey Challenges: Hard to get High Cr concentration Hard to get Uniform Cr distribution Hard to make Large Cr2+:ZnSe

crystals

High scattering loss Low damage threshold Strong thermal lensing effects

Our goal was to improve quality of the Cr:ZnSe/S and optimize crystal geometry to obtain multi-watt CW lasing in non-selective, dispersive and microchip modes of operation.

27

Pulsed Laser Deposition Growth of Thin Films

Target: ZnS/Fe Substrate: Si at 550oC

or 650oC Target-substrate

separation: 5 ~ 10cm Pressure vacuum: 2.6

10-6 torr Laser: 248nm KrF, 30

Hz rate, energy density 2J/cm2

Post annealing is applied

S. Wang, S. B. Mirov, V. V. Fedorov, R. P. Camata, “Synthesis and spectroscopic properties of Cr doped ZnS crystalline thin films” in Solid State Lasers XIII: Technology and Devices, Proceedings of the International Society of Optical Engineering (SPIE) (2004) Vol. 5332, 13-20 Editors: Richard Scheps, Hanna J. Hoffman (ISBN 0-8194-5240-8)

28

Surface & cross section SEM (ZnS results)

Cross section 2500x Surface 5000x

1.5 hours deposition + 1 hour post annealing, at 550oC substrate temperature

S. Wang, S. B. Mirov, V. V. Fedorov, R. P. Camata, “Synthesis and spectroscopic properties of Cr doped ZnS crystalline thin films” in Solid State Lasers XIII: Technology and Devices, Proceedings of the International Society of Optical Engineering (SPIE) (2004) Vol. 5332, 13-20 Editors: Richard Scheps, Hanna J. Hoffman (ISBN 0-8194-5240-8)

29

Hot-pressed Ceramic Preparation

Abs. Energy (mJ)0 10 20 30 40 50 60

Out

put E

nerg

y (m

J)

0

1

2

BC

=3%=5%

ZnSe+ CrSe(0.1-0.01%)

ZnSe

P=60MPa

ZnSe+ CrSe(1%) 15 mm

P=30-350MPa

A. Gallian, V. V. Fedorov, S. B. Mirov, V. V. Badikov, S. N. Galkin, E. F. Voronkin, and A. I. Lalayants, " Hot-pressed ceramic Cr2+:ZnSe gain-switched laser ," Opt. Express 14, 11694-11701 (2006).

B

Pabs, W0.5 1.0 1.5

Pout

, mW

0

50

100

150

200

250

300

i

iiOC 10%

OC 5%

CW regime

Gain-switched regime

30

Bulk Crystal Preparation by post-growth thermal diffusion

P=10-5 torrT= 950-1000 C t=3-10 days

Thermal annealing

The polished samples of up to 7 mm thickness can be prepared

Crystal growth or Infrared window purchase

Powder

Crystal

Crystal

S.B. Mirov, V.V. Fedorov, (November 1, 2005) Mid‐IR microchip laser: ZnS:Cr2+ laser and saturation absorption material”, US Patent No 6,960,486.

Cr thin film deposition

• Uniformly-doped, reasonably large samples;

• Low scattering loss in thermally diffusion doped crystals;

• Strong thermal lensing effects;

Good for High-Power (tunable) Lasers

5 mm3

9

7

k~3 cm-1 @ 1.56 m

Cross-section cut from the middle shows uniform Cr distribution

Power‐Scaling of Cr:ZnSe CW LasersNew Technology: High‐Quality Cr2+:ZnSe Crystals

Key Properties:• Uniform Cr distribution• Negligible scattering loss• Pre-assigned Cr concentration• Large, engineered (undoped ends,

gradient concentration) crystals are feasible

Uniformly-doped5x5x20 mm crystal

31

R1R2 d1

d2

d3

Pump lens

1.56 m Pump

Beam

Cr2+ZnSe

Cavity parameters: Pump lens: f=75 mm; R1=50 mm; R2=50 mm; d1=55 mm; d2=26 mm; d3=100 mm;

Power‐Scaling of Cr2+:ZnSe CW Lasers: Cavity Configuration

Pump Lasers Available:1. 9.5 W Linearly-Polarized

Er-fiber Laser; Up to 7.5 W could be used due to losses on delivering optics;

2. 30 W Randomly-Polarized Er-fiber Laser; Up to 13 W could be used due to Fresnel loss on the Brewster surface of the laser crystal;

Compact, Folded, 3-mirror Kogelnik Cavity:Easy to align;Brewster astigmatism compensation;Good output beam quality obtainable; Convenient mode-size control;Crystal geometry:Thin 2.5x7x9mm slab placed between twoair-cooled Cu heat sinks

32

Previously reported state-of-the-art: 1.4 W, CW, 4.2 @ 10kHz thin-disk

laser by Schepler et al (2005) 1.8 W, CW Kogelnik cavity by

Wagner et al (2001) 18.5 QCW (duty cycle10-3) Carrig

et al (2004)

I.S. Moskalev, V. V. Fedorov, and S. B. Mirov, Optics Express 16(6), 4145-4153 (2008).

High-Power Cr2+:ZnSe Polycrystalline CW Laser: New Technology Crystals

Pumped by randomly-polarized Er-fiber laser 33

I.S. Moskalev, V. V. Fedorov, and S. B. Mirov, Optics Express 16(6), 4145-4153 (2008).

34

State of the art in Cr:ZnS and ZnSe microchips

nm2550 2600

Inte

nsity

, arb

.un.

Cr2+:ZnS

nm2300 2350

Inte

nsity

, arb

. un.

Cr2+:ZnSeA

B

A

B

2400 2600

C

Pabs,W0 1 2 3 4

Pout

,W

0 .0

0.1

0.2

0.3

0.4

0.5

0.6

Ge Filter

Output coupler3.5% transmission over 2300-2500 nm

Coupling optics

Er fiber or diode

laser

ZnS:Cr2+ (d=1 mm) or ZnSe:Cr2+ (d=2.5 mm)

CrystalInput mirror

1.55-1.9 m

2280-2360 m (ZnS) 2480-2590m (ZnSe)

Cr:ZnSe microchip

mm-10 -8 -6 -4 -2 0 2 4 6 8 10 12 14

Inte

nsity

, arb

. un.

0.0

0.2

0.4

0.6

0.8

1.0

High-Power Cr2+:ZnSe Polycrystalline Microchip CW Laser

Input mirror UncoatedCr2+:ZnSe 9x7x3 mm

2 ~ 1.3 mrad

M2~2.2

AR@1.56 m HR@2.1-2.8 m

Positive thermal lens forms a stable resonator within theplane-plane cavity;The output power roll-off occurs due to change in the

thermal lens focal length as the intracavity light intensity is increased; 35

I.S. Moskalev, V. V. Fedorov, and S. B. Mirov, Optics Express 16(6), 4145-4153 (2008).

Cr:ZnSe Single-Frequency CW Laser: SetupKey Features: • Kogelnik – Littman Folded Cavity; • Rapidly tilted tuning mirror: 10--220 Hz;• Fiber-laser pumping: 1.56 m, 7 W max;• TEC/AIR cooling;

Distances: d1=d2=25 mm, d3=30 mm, d4=20 mm. Mirrors and lenses: R1=25 mm, R2=50 mm, Pump lens f=50 mm. D1 and D2 optical detectors.

D2

R1R2

Grating 600 g/mm

Tuning mirror Output beam

d1d2

d3

d4

Pump lens

WavemeterD1 Scanning

FPI

1.56 m Er-fiber laser

Key Results:Compact design: 10 cm and smaller; High output power: 150 mW at 5 W pumpWide tuning range: 2440-2560 nm;Narrow linewidth: 80-130 MHz;Rapid wavelength tuning: 4.5 m/s;

36Previously reported state-of-the-art: 20 MHz, 10 mW @ 2460 nm. Grating and 2 FP etalons. Carrig (ASSP’ 2004)

I.S. Moskalev, V. V. Fedorov, and S. B. Mirov, Optics Express 16(6), 4145-4153 (2008).

High-power, widely tunable polycrystalline CW Cr2+:ZnSe laser

7x3x9 mm (9 mm is the length), uniformly-doped polycrystalline Cr2+:ZnSe crystal (absorption coefficient k~4 cm-1 at 1.56 µm pump radiation. X-type Littrow grating cavity, the total cavity length is 30 cm, the whole laser system fits

on the 20x25 cm breadboard. The 95% efficient (at 45 incident angle), 600 g/mm Littrow diffraction grating is

mounted on a computer controlled rotation stage and the laser wavelength tuning is performed with “one knob” over the entire tuning range of 2.12-2.77 µm.

High-power, widely tunable polycrystalline CW Cr2+:ZnSe laser

~ 1 nm, real=20%I.S. Moskalev, V. V. Fedorov, and S. B. Mirov, Optics Express 16(6), 4145-4153 (2008).

l d1d0z

wm wc wD

wgActive

mediumLens L1

Mirror M1

Aperture A

1

2 3

Spatial mask

x

Pump Beam

I

x

I

fx

ft

ft

dxd 2

024

cos2

)sin(2 tk

xILT

TI pumpSTabsosc

oscpump IxI

20

20 4 t

fx

where

“Spatially Dispersive” Multiline and ultrabroadband lasersU.S. Patent No. 5,471,493, U.S. Patent No 6,236,666 “Application of laser beam shaping for spectral control of “spatially dispersive” lasers” Chapter 7, pp.241‐267, in Laser Beam Shaping Applications, Dickey, Holswade, Shealy ‐ Eds., Taylor & Francis, ISBN 0‐8247‐5941‐9, 2005.

40

Multiline and ultrabroadband lasersU.S. Patent No. 5,471,493, U.S. Patent No 6,236,666 “Application of laser beam shaping for spectral control of “spatially dispersive” lasers” Chapter 7, pp.241‐267, in Laser Beam Shaping Applications, Dickey, Holswade, Shealy ‐ Eds., Taylor & Francis, ISBN 0‐8247‐5941‐9, 2005.

Wavelengh, m1.10 1.15 1.20 1.25

I, a.

e.

0

1

640 645 650 655 660 665 670 675 680

Inte

nsity

, rel

ativ

e un

its

0.0

0.2

0.4

0.6

0.8

1.0luminescencemultiline lasing

LiF CCL Multiline 1& 2 Multiline diode laser Multiline Cr2+:ZnSe

I. Moskalev, et. al. Optics Express 12, 2004

T. Basiev et al., Appl. Optics 36, 2515 1997

I. Moskalev et al. Opt. Comm. 220, 161 2003

(b)

Wavelength, nm

1550 1560 1570 1580 1590In

tens

ity, r

elat

ive

units

0.0

0.2

0.4

0.6

0.8

1.0luminescencemultiline lasing

41

Fe2+:ZnSe problemIt was believed that because of the small energy gap , thermally activated multiphonon quenching in Fe:ZnSe mandates cryogenic laser operation.

PL lifetime vs temperature (Adams, OL24, 1720 (1999)

Possible solution – gain switched regime of operation with pump pulse duration shorter than Fe2+ lifetime at 300K

42

RT Fe:ZnSe Lasing in nonselective and prism Cavity

Wavelength, m

4.0 4.2 4.4 4.6 4.8 5.0 5.2O

utpu

t Ene

rgy,

mJ

0.00

0.25

0.50

Absorped Energy, mJ

0 1 2 3 4 5

Out

put E

nerg

y, m

J

0.0

0.1

0.2

0.3

0.4

IEEE J. of Quantum Electronics 42 (9), 907‐917, September 2006

Input-Output characteristics of the gain switched Fe2+:ZnSe laser at RT.

Tuning curve of room-temperature Fe2+:ZnSe laser with intra-cavity prism obtained at absorbed pump energy of 4.5 mJ.

Fe doped CdMnTe crystals – promising gain media for 4000-6500 nm lasing

Fe2+ (RT)

Wavelength(nm)

2000 3000 4000 5000 6000 7000 8000 9000

Abs

orpt

ion,

cm

-1

0

5

10

15

20

25

30

ZnSeCdMnTe

CO2

A

time, us0 20 40 60

sign

al V

10-3

10-2

10-1

B

T, K

0 50 100 150 200 250 300

life

-tim

e, u

s

0.1

1

10

100

i

ii

iiiiv

v

vi

wavelength, nm

3500 4000 4500 5000 5500 6000 6500 7000

Inte

nsity

, a.u

Pump Second Order

CO2 absorption14K

RT

43

W. Mallory, Jr., V. V. Fedorov, S. B. Mirov, U. Hömmerich, W. Palosz, and S. B. Trivedi, Proc. of SPIE Vol. 6871, 68712T (2008).

Fe:ZnSe passively Q-Switched Er:Cr:YSGG laser

1 pulse13 mJ30 J pump40% efficiencyScheme (b)

19 pulses85 mJ30 J pump40% R OCScheme (a)

5 pulses25 mJ20 J pump40% R OCScheme (a)

Andrew Gallian , Alan Martinez , Patrick Marine , Vladimir Fedorov , Sergey Mirov*, Valeri Badikov D. M. Boutoussov, and M. Andriasyan,

“Fe:ZnSe passive q-switching of 2.8-µm Er:Cr:YSGG laser Cavity”, Proceedings SPIE Vol. 6451 (SPIE, Bellingham, WE, 2007)..

T=90%

1 pulse 6 mJ & 7J pump for 80% R OC

44

2.8m 2.94m

The combination of a high values of saturation cross-section (0.9x10-18 cm2, small saturation energy with good opto-mechanical (damage threshold - 2J/cm2) and physical characteristics of ZnSe and ZnS hosts make Fe2+:ZnSe/S crystals an ideal materials for passive Q-switching of mid-infrared laser cavities.

Single frequency Cr:ZnSe passively Q-Switched Er:YAG

45

f=400 mm34 mm2 mm

10 mm

Bragggrating

1.0%, 30 mm Er:YAG

45 mm

f=75 mm

370 mm

35 mm

Cr2+:ZnSe Q-switch

Flat 100% end mirror

Schematic diagram of the optical scheme of the passively Q-switched Er:YAG laser.

I. Moskalev, et al., Optics Express, 2008 in preparation

Cr2+:ZnSe

Wavelength, nm1000 1500 2000 2500

x10

-18 cm

2

0.0

0.5

1.0 1.645m

Single frequency Cr:ZnSe passively Q-Switched Er:YAG

46

Er:YAG Passively Q-switched laser output Power vs pump

Pump power, W2 4 6 8 10 12 14 16

Ave

rage

Out

put P

ower

, W

0

1

2

3

4

5 CW, real~30%, slope~42% Q-switched, real~14%, slope~20%

7 kHz Passively Q-switched Er:YAG laser SLM pulse

Time, ns0 50 100 150 200 250 300 350 400

Sign

al, a

.u.

0.0

0.2

0.4

0.6

0.8

1.0FWHM ~ 65 ns

SLM Passively Q-switched Er:YAG laser pulse train

Time, s0.000 0.001 0.002 0.003

Sig

nal,

a.u.

0.0

0.2

0.4

0.6

0.8

1.0

I. Moskalev, et al., Optics Express, 2008 in preparation

Cr2+:ZnSe and Cr2+:ZnS saturable absorbers are ideal materials for passive Q-switches of eye-safe fiber and solid-state lasers operating in the spectral range of 1.5-2.1 m.

47

Future electrically pumped Cr and Fe doped Quantum Dot and Quantum well broadly tunable mid-IR lasers

Cr and Fe doped II-VI lasers combine the versatility of the ion-doped solid-state lasers with the engineering capabilities of semiconductor lasers, paving the route to the future electrically pumped ultrabroad-band solid-state lasers.Why QD and QW structures are so critical for

electrical excitation? For successful realization of electrical excitation two

conditions should be satisfied: (i) effective and sustainable excitation of the crystal host by electrical current, and (ii) effective energy transfer from the host to the mid-IR lasing TM impurity.

The phenomena of quantum confinement of the atomic impurity in quantum well and quantum dot active layers results in much more efficient transfer of energy from the host to the localized impurity due to a large increase of exciton oscillator strength bound to the impurity center.

SSDLTR’08, Mid‐Infrared Lasers

48

Future electrically pumped Cr and Fe doped Quantum Dot and Quantum well broadly tunable mid-IR lasers

Scheme of the Mid‐IR laser based on QW Cr:ZnSe heterostructure.

GaAs Substrate n-ZnSe Chromium

doped ZnCdSe QW

p-ZnSe

Molecular beam epitaxy

2 µm 3 µmwavelengthIn

ten

sity

2 µm 3 µmwavelengthIn

ten

sity

~100 m

2-3 mm

P - Contact

p - Clad Layer

Nanocomposite Active Region

n - Clad Layer

n+ - Substrate

N- Contact

Scheme of the Mid‐IR laser based on nanocomposite QW/QD Cr:ZnSe ‐conductive polymer structure prepared by layer by layer method

n‐GaAs substrate

n+‐ZnSe

n‐ZnxMg1‐xSySe1‐y

p‐ZnxMg1‐xSySe1‐y

In electrode

Au electrode

p‐ZnS1‐xSex

n‐ZnS1‐xSex

2‐5 µm Cladding

2‐5 µm

1‐2 µm Guiding

J. of Luminescence 125, 184‐195 (2007)

Cr:ZnCdSe

49

Lasing of Cr2+:ZnSe via Ionization Transitions

s0 2 4 6 8

mV

05

10152025

0 2 4

Pump Pulse

Lasing from 532nm pumping

Lasing from 1560nm

pumping

s

Build up time

Lasing from 532nm pumping

PumpEnergy, mJ5 10 15Lasi

ng In

tens

ity, a

b.un

.

05

10152025

Wavelength, nm1800 2000 2200 2400 2600 2800 30000

1

Inte

nsity

, ab.

un. Lasing from

532nm pumping

Luminescence from 532nm pumping

Lasing and Luminescence spectra under 532nm excitation

ZnSeCB

VB

Eac

Ed

Cr2+/Cr+

+ +

hpump

hos

Cr2+*

5E

5T2

Cr2+*

J. of Luminescence 125, 184‐195 (2007)

532nm, 5nsec pulse

10Hz rep rate

10cm Au Mirror

Cr2+:ZnSe1mmx4mm

95% R Flat Output Coupler

50

Mid-IR Electroluminescence of n-Cr:ZnSe (ASSP’06 WB21)Absorption Spectra Al:Cr:ZnSe

K (cm

-1)

0

2

4

6

8

Wavelength (nm)1200 1600 1800 2000

I-V Curves for Cr-Al:ZnSe Samples # 1 & 2

Voltage(V)-80 -60 -40 -20 0 20 40 60 80

Cur

rent

(mA

)

-10-8-6-4-2

246810

Sample#2

Sample#10

~30KΩ

~7.5KΩ

Time (µs)-200 0

Volts

-2

mid-IR optical signal

Electrical pulse

200

-4

Visible Luminescence ofVZn-Al complex

Inte

nsity

, a.u

.

mid-IR Cr2+ electroluminescence

Wavelength (nm)

Inte

nsity

, a.u

.

Wavelength (nm)400 600 800 1800 2200 2600

Cr2+ optical pumping

The nanocrystals were fabricated from TM (Cr, Co, Fe) thermo-diffusion doped ZnS and ZnSe bulk crystals

At the first step of NCD preparation, bulk polycrystalline samples were ablated by Nd:YAG laser with (1064nm) pulse duration 30 ps, repetition rate 10 Hz, and pulse energy of 10 mJ.

At the second step of preparation nanoparticles suspension was sonicated in order to break large aggregate. The radiation of the third harmonic (355nm) of the Nd:YAG laser with 30 ps, 10 Hz, and 15 mJ.

Precipitated nanoparticles were extracted from aqueous solution, washed with distilled-deionizer water and dried naturally under ambient condition

Experimental setup of Ⅱ-Ⅵ semiconductorNanocrystalline dot (NCD) fabrication by laser ablationbulk TM:II-VI in liquid.

Fabrication of II-VI NCD doped with TM (Cr, Co and Fe) ions by laser ablation method

51

Laser beam

H20

ZnSFilter

Peristaltic pump

Laser beam

ZnS ArIn

Out

Filter

C. Kim, D. V. Martyshkin, V.V. Fedorov, I. S. Moskalev, S. B. Mirov, J. of Spectroscopy, 22(9), 32-37 (2007).

First mid-IR luminescence of TM doped II-VI NCD

C. Kim, D. V. Martyshkin, V.V. Fedorov, I. S. Moskalev, S. B. Mirov, J. of Spectroscopy, 22(9), 32-37 (2007).

1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

FeCoCr

Wavelength, m

RT luminescence spectra of a) Cr, b) Co and c) Fe doped ZnSe NCs samples.

We have developed technique for preparation of nanoparticles based on II-VI materials doped with TM ions with photoluminescence in mid-IR spectral region

Lasing of 27 nm Cr2+:ZnS NCsLasing spectra and energy input-outputcharacteristics of 27 nm Cr2+:ZnS NCs. RTemission of the Cr2+:ZnS NCs under 1.56m excitation with pump energy below (a)and at laser threshold (b), c) Spectrum ofthe RT lasing of the Cr2+:ZnS NCs, d)Output-input dependence for RT gain-switched Cr:ZnS NCs lasing. Thepumping beam size was 3 mmcorresponding to ~310 mJ/cm2 thresholdpump energy density.

QELS’08 D. Martyshkin, et al., QFD2

0 5 10 15 20 25 30 35

27 nm250 nm3 m

Inte

nsity

Energy (mJ)

Laser action was monitored by threshold behavior of intensity, emission spectra and shortening of emission lifetime

27 nm Cr:ZnS NCs lasing

Potential Applications1. The ability of the II-VI lasers to tune in and out of the strong absorption band of liquid

water will definitely make use for surgical applications: welding applications (power requirement is ~ 200 mW, which is already available), or surgical scalpels applications (~10 W, which is already available).

2. The ability of the II-VI lasers to tune in resonance with absorption of numerous organic molecules over 2-5 m and in tandem with OPO over 2-15 m spectral range make them promising for:

Species-specific gas monitoring in production facilities Sensing of pollution and chemical warfare agents; Monitoring of hazardous waste and munitions disposal Tracking of naturally occurring gas emitters - methane seeps and volcanoes Stand-off assessment of explosion hazards such as fuel leaks Oil prospecting Measurements of medically important molecular compounds in the exhaled breath of patients, or

other medical applications such as non-invasive optical blood glucose monitoring around 2.3 um through the human skin.

3. The ability of the II-VI lasers to operate over windows of atmospheric transparency makes these lasers suitable for Infrared countermeasures eyesafe seekers for smart munitions and cruise missiles; oratmospheric free space communications.

4. The combination of a high values of saturation cross-section (10-18 cm2), small saturation energy with good opto-mechanical (damage threshold - 2J/cm2) and physical characteristics of ZnSe and ZnS hosts make Cr and Fe2+:ZnSe/S crystals an ideal materials for passive Q-switching of mid-infrared laser cavities.

55

Conclusions Recent progress in transition metal doped II‐VI semiconductor materials

(mainly Cr2+:ZnSe and ZnS) make them the laser sources of choice whenone needs a compact system with continuous tunability over 2‐3.1 m,output powers up to 6W, and high (up to 70%) conversion efficiency.

The unique combination of technological (low‐cost ceramic material) andspectroscopic characteristics (ultra‐broadband gain bandwidth, high product and high absorption coefficients) make these materials idealcandidates for “non‐traditional” regimes of operation such as microchip(output power up to 3W) and multi‐line lasing – (lasing with any pre‐assigned spectral composition‐dozens of lines).

Emerging Fe2+:chalcogenide lasers have potential to operate at roomtemperature over the spectral range extended to 3.7‐6.5 m.

Cr and Fe doped II‐VI lasers combine the versatility of the ion‐doped solid‐state lasers with the engineering capabilities of semiconductor lasers, paving the route to the future electrically pumped ultrabroad‐band solid‐state lasers. This work shows the initial steps towards achieving this goal by studying Cr2+ ion excitation into the upper laser state 5E via photo‐ionization transitions as well as via direct electrical excitation. First mid‐IR luminescense of Cr, Co, and Fe doped quantum dots was demonstrated at RT over 2‐5 m spectral range as well as first lasing of Cr doped ZnS quantum dots.

Future Plans Optimization of Cr/Fe:ZnSe laser ceramic. Cr:ZnSe/S Power scaling to 0.1-1 kW power

levels 20 x 5 x 1-mm edge-pumped slab, with uniform heating, could dissipate as much as 1.6 kW of heat before fracturing. If we assume a pump laser at 1600 nm and a Cr:ZnSe laser operating at 2400 nm, then 1/3 of the pump power is dissipated as heat, so the slab could be pumped with nearly 5 kW of pump before fracture.

High output energy (tens of mJ, tens of ns) gain switched (room temperature Cr:ZnSe/S 2-3m and Fe:ZnSe (3.8-5.2 m) lasers.

High output energy (hundreds of mJ, hundreds of s) pulsed room temperature Cr:ZnSe/S (2-3m) and Fe:ZnSe (3.8-5.2 m) lasers.

Er/Tm fiber pumped CW TE cooled Cr/Co/Fe:ZnSe 3.8-5.2 m lasers.

Multiline spatially dispersive Cr/Fe:ZnSe lasers. Search for new Fe:II-VI laser media promising

for 3-7 m gain switched lasing at RT Electrically pumped QD/QW 2-3m Cr:ZnSe/S

lasers.

Opt. Express 14, 11694-11701 (2006) J. of Spec. Top. in QE., 13(3), 810-822, 2007.IEEE J. of QE 42 (9), 907-917 (2006).J. of Luminescence 125J. of Spectroscopy, 22(9), 184-195 (2007)

1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

FeC oC r

W avelength, m

wavelength, nm

3500 4000 4500 5000 5500 6000 6500 7000

Inte

nsity

, a.u

Pump Second Order

CO2 absorption14K

RT

Fe:CdMnTe

TM:ZnSe QD