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8/13/2019 Presentation PCF High Repetition Rate
1/59
Fraunhofer IOF
5th international workshop on fiber lasers in Dresden 2009
High repetition rate short pulse fiber lasers and
amplifiers: Fundamentals and perspectives
Andreas Tnnermann
Fraunhofer-Institut fr Angewandte Optik
und Feinmechanik IOFAlbert-Einstein-Strae 7
07745 Jena
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Fraunhofer IOF
Laser Focus World 2009, Author: Gail Overton, Stephen G. Anderson
percentage of overall laser revenues
Laser by application
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Fraunhofer IOF
solid state laser market (2008):1,500 Mio. US$
Laser Focus World 2009, Author: Gail Overton, Stephen G. Anderson
Laser by technology
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Fraunhofer IOF
Fiber laser market
others; 27%
medicine;7%
material
processing ;67%
others;23%
medicine;
7%material
processing;70%
2005105 Mio. US$
2008300 Mio. US$
fiber laser market:annual growth + 40%
source: Optech Consulting
8/13/2019 Presentation PCF High Repetition Rate
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Fraunhofer IOF
Fiber lasers basic principlesHigh power, high energy nanosecond fiber amplifiers
High power femtosecond fiber amplifiers
Laser micromachining
Conclusion
Outline
8/13/2019 Presentation PCF High Repetition Rate
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Fraunhofer IOF
power combiner
active fiber
power supplypump diodes
OC (LR FBG)HR FBG
Fiber laser: basic principle
8/13/2019 Presentation PCF High Repetition Rate
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8/13/2019 Presentation PCF High Repetition Rate
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Fraunhofer IOF
inelastic scattering process of photons on optical phonons
1050 1075 1100 1125 1150 1175 1200
1. StokesLaser
Laserlesitung 100 W 110 W 120 W
i n t e n s i
t y [ a
. E . ]
wavelength [nm]
pP E h=
sS E h=f i EE
Raman-spectrum
Reff
eff SRS g L
AP 16
gB
= Raman-gain coefficient,Aeff = eff. areaLeff = effective interaction lengthG.P. Agrawal Nonlinear fiber optics,Academic Press, 1995
THz pS 13 in silica
0 6 12 18 24 30 36 420,0
0,2
0,4
0,6
0,8
1,0
R a m a n - g a i n
[ * 1 0 - 1
3 m
/ W ]
frequency shift [THz]
Raman-gain coefficient
R. H. Stolen, Proc. IEEE, 68, 1232, 1980
Power scaling limitation nonlinearity (SRS)
8/13/2019 Presentation PCF High Repetition Rate
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8/13/2019 Presentation PCF High Repetition Rate
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Fraunhofer IOF
microstructured fiber
air
glass d
step-index fiber
2a
n coren cladding
n ~ 110 -4
NA ~ 0.02 n ~ 110 -3
NA ~ 0.06
significantly larger single-mode core possible
N.A. Mortensen, J.R. Folkenberg, M.D. Nielsen, and K.P. Hansen, "Modal cut-off and the V-parameter in photonic crystal
fibers", Opt. Lett. 28, 1879 (2003).
Microstructured fibers
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Fraunhofer IOF
taken from: Kim P. Hansen et.al.
Photonic Crystal Fibers, Photonics West 2005
Air cladding region high NA inner cladding
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Fraunhofer IOF
inner cladding: = 170 .. 210 m (NA > 0.6) ACcore: = 40 .. 50 m, NA = 0.03, MFD ~ 45 m
pump light absorption: >10 dB/m @ 976 nm
strictly single-mode operation with a MFA ~1000 .. 1600 m 2 !!!
outer claddingair-clad
inner cladding
active core
M2 < 1.2
J. Limpert, Low-nonlinearity single-transverse-mode ytterbium-doped photonic crystal fiber amplifier, Opt. Express 12,
1313-1319 (2004).
Extended large-mode-area single-mode RE-doped PCF
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Fraunhofer IOF
ORC-Southampton,
Great BritanTokyo University,Japan
FSU-IAP, FhG-IOF &IPHT, Jena, Germany
University of Michigan,USA
IPGSPIJDSU / SDLJenoptikNufernCrystal Fibre
1992 1994 1996 1998 2000 2002 2004 20060
200400
600
800
1000
1200
1400
1600
1800
2000step index fiber photonic crystal fiber
370 W
1530 W
2000 W
1360 W
260 W
80 W4 W
1300 W
800 W
600 W
135 W200 W
400 W
150 W170 W
485 W
110 W9,2 W5 W 30 W
270 W
C W
o u
t p u t p o w e r
[ W ]
Year
1900 W
evolution of cw fiber laser
Diode-pumped double clad fiber laser (cw output)
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Fraunhofer IOF
2002 2003 2004 2005 2006 2007 2008 2009100
1000
10000
IAP
IAP+IOF IPG IPHT+IAP SPI JO+IAP Michigan
O u t p u t
P o w e r
/ W
Year
Diode-pumped double clad fiber laser (cw output)evolution of cw fiber laser
8/13/2019 Presentation PCF High Repetition Rate
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Fraunhofer IOF
laser core(generated heat)pump corecoating
one-dimensional heat conduction equation
0r K r Q
dr r dT
r 1
dr Td 2
2
=+
+
)(
)()(
Q: generated heat per unit volumeK: thermal conductivity
0 1 2 3 4 50 100 150 200 250 300 350
region of thepump core
region of thelaser core
T [ a
. u . ]
radius [m]
heat conduction
radiative heat dissipationand convective heat flow
TdAdQ k convection =
( )4241radiation TTdAdQ = k: heat transition coefficient
: Stefan-Boltzmann-constant
: emission factor
Temperature profile
Thermo-optical effects
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Fraunhofer IOF
0 2 4 6 8 10 12 14 16 18 20 22 240
2
4
6
8
10
12
1200 W/m extracted
damage threshold
SRS threshold
P o w e r
[ k W ]
Fiber length [m]
@ 40 m core diameter
cw 10 kW-class single-mode fiber laser
Power scaling limitations
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Fraunhofer IOF
ILT, IOF, IWS, IFSW
r F
F
r = r F F
BPP = r
r
beam power [W]
b e a m p a r a m e t e r p r o
d u c t
B P P [ m m m r a
d ]
0,1
1
10
100
10 100 1000 10000
diode laser
fibre laserdisc laser
Nd:YAG-laser
CO 2 -laser
High power lasers: beam quality and output power
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Fraunhofer IOF
Outline
Fiber lasers basic principles
High power, high energy nanosecond fiber amplifiers
High power femtosecond fiber amplifiers
Laser micromachining
Conclusion
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Fraunhofer IOF
seed source
isolator
pre-amp booster
ASE filter isolator
end-cap
Pulsed fiber laser MOPA
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Fraunhofer IOF
Input Output
OutputInput
Pulsed fiber laser MOPA
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Fraunhofer IOF
Digital functiongenerator (50kHz)
Analog pulsegenerator + delay
Ch1
Ch2Ch3Ch4
ECDL
30cm, PM-6m
WDM
SM-pump(976nm)
2m, PM-10/125
electronics
pump(976nm)
grating(ASE-filter)
pinhole
pump(976nm)
to combiningstage
1.2m, rod-type PCF, 80/2002
4
Pulsed fiber laser MOPA - 3-stage amplifier
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Fraunhofer IOF
Digital functiongenerator (50kHz)
Analog pulsegenerator + delay
Ch1
Ch2Ch3Ch4
ECDL
30cm, PM-6m
WDM
SM-pump(976nm)
2m, PM-10/125
electronics
pump(976nm)
grating(ASE-filter)
pinhole
pump(976nm)
to combiningstage
1.2m, rod-type PCF, 80/2002
4
5W
Pulsed fiber laser MOPA diode laser seed source
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Fraunhofer IOF
Digital functiongenerator (50kHz)
Analog pulsegenerator + delay
Ch1
Ch2Ch3Ch4
ECDL
30cm, PM-6m
WDM
SM-pump(976nm)
2m, PM-10/125
electronics
pump(976nm)
grating(ASE-filter)
pinhole
pump(976nm)
to combiningstage
1.2m, rod-type PCF, 80/2002
4
Pulsed fiber laser MOPA - electronics
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Fraunhofer IOF
Digital functiongenerator (50kHz)
Analog pulsegenerator + delay
Ch1
Ch2Ch3Ch4
ECDL
30cm, PM-6m
WDM
SM-pump(976nm)
2m, PM-10/125
electronics
pump(976nm)
grating(ASE-filter)
pinholepump
(976nm)
to combiningstage
1.2m, rod-type PCF, 80/2002
4
Pulsed fiber laser MOPA - electronics
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Fraunhofer IOF
Digital functiongenerator (50kHz)
Analog pulsegenerator + delay
Ch1
Ch2Ch3Ch4
ECDL
30cm, PM-6m
WDM
SM-pump(976nm)
2m, PM-10/125
electronics
pump(976nm)
grating(ASE-filter)
pinhole
pump(976nm)
to combiningstage
1.2m, rod-type PCF, 80/2002
4
~1mW
5W
Pulsed fiber laser MOPA 1st preamplifier
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Fraunhofer IOF
Digital functiongenerator (50kHz)
Analog pulsegenerator + delay
Ch1
Ch2Ch3Ch4
ECDL
30cm, PM-6m
WDM
SM-pump(976nm)
2m, PM-10/125
electronics
pump(976nm)
grating(ASE-filter)
pinhole
pump(976nm)
to combiningstage
1.2m, rod-type PCF, 80/2002
4 0.1W
Pulsed fiber laser MOPA 2nd preamplifier
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Fraunhofer IOF
Digital functiongenerator (50kHz)
Analog pulsegenerator + delay
Ch1
Ch2Ch3Ch4
ECDL
30cm, PM-6m
WDM
SM-pump(976nm)
2m, PM-10/125
electronics
pump(976nm)
grating(ASE-filter)
pinholepump
(976nm)
to combiningstage
1.2m, rod-type PCF, 80/2002
4
1031 1032 1033 1034 1035-90
-80
-70
-60
-50
-40
-30
-20-10
S p e c
t r a l
p o w e r
[ d B ]
Wavelength [nm]
Pulsed fiber laser MOPA ASE-filter
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Fraunhofer IOF
Digital functiongenerator (50kHz)
Analog pulsegenerator + delay
Ch1
Ch2Ch3Ch4
ECDL
30cm, PM-6m
WDM
SM-pump(976nm)
2m, PM-10/125
electronics
pump(976nm)
grating(ASE-filter)
pinhole
pump(976nm)
to combiningstage
1.2m, rod-type PCF, 80/2002
4 ~50 W1 mJ
Pump core
(200 m)
Active core(80 m)
Air clad
MFD ~ 70 mMFA ~ 4000 m 2
Low nonlinearites!
Pulsed fiber laser MOPA power amplifier
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Fraunhofer IOF
system parameters: o) number of channels = 4o) pulse repetition rate = 50 kHzo) pulse duration = 2.2 ns
Reflection grating
Output
3-stage amplifier
Combining stage
12
34
Sources
:
:
:
Pulsed fiber laser MOPA spectral combining
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P l d fib l MOPA l bi i
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Fraunhofer IOF
Dielectric reflectiongrating
(1030 nm)
(1032nm)
(1034 nm)(1036 nm)
Combinedoutput
(1740 lines/mm)
Folding mirrors
combining efficiency 97%
Pavg
= 187 WEpulse = 3.7 mJP peak = 1.7 MW
Pulsed fiber laser MOPA spectral combining
P l d fib l MOPA hi h titi t
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Fraunhofer IOF
Digital functiongenerator:
f Rep = 5 MHz
Analog pulsegenerator:
5 ns pulses + delay
Ch1
Ch2Ch3Ch4
ECDL
30 cm PM-6m
WDM
SM-LD2 m PM-10/125
electronics
LD
1.6 m PZ-40/200
LD
LD15 m 42/500
Single output
HWP
IF
water-cooled
Pulsed fiber laser MOPA high repetition rate
P l d fib l MOPA high titi t
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Fraunhofer IOF
f rep = 5 MHz, T pulse = 5 ns, 4 laser systems
1032 1034 1036 1038 1040 1042 1044 1046-80
-70
-60
-50
-40
-30
-20
-10
0
4nm
Channel 4Channel 3Channel 2Channel 1
S p e c
t r a l p o w e r
[ d B ]
Wavelength [nm]
Main amplifier fiber
Length ~ 15 mpump core ~ 500 m
active core ~ 42 m
Pulsed fiber laser MOPA high repetition rate
Pulsed fiber laser MOPA high repetition rate
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Fraunhofer IOF
Slope efficiency = 49%
1.1 kWCombining efficiency = 99%
Epulse = 220 J
0 500 1000 1500 2000 25000
200
400
600
800
1000
1200
A v e r a g e o u
t p u
t p o w e r [
W ]
Launched pump power [W]
1.0
1.5
2.0
2.5
3.0
M 2 x
( h o r i z o n
t a l )
combined beam
Pulsed fiber laser MOPA high repetition rate
Nanosecond pulsed fiber laser MOPA
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Fraunhofer IOF
f rep = 50 kHz, T pulse = 2.2 nsP avg = 187 W
Epulse = 3.7 mJP peak = 1.7 MW
f rep = 5 MHz, T pulse = 5 nsP avg = 1100 W
Epulse = 220 JP peak = 44 kW
high pulse energy high average power
O. Schmidt, C. Wirth, I. Tsybin, T. Schreiber, R. Eberhardt,J. Limpert, and A. Tnnermann, "Average power of 1.1 kW
from spectrally combined, fiber-amplified, nanosecond-pulsedsources," Opt. Lett. 34, 1567-1569 (2009).
O. Schmidt, T. V. Andersen, J. Limpert, and A.Tnnermann, "187 W, 3.7 mJ from spectrally combinedpulsed 2 ns fiber amplifiers," Opt. Lett. 34, 226-228(2009).
Nanosecond pulsed fiber laser MOPA
Outline
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Fraunhofer IOF
Outline
Fiber lasers basic principles
High power, high energy nanosecond fiber amplifiers
High power femtosecond fiber amplifiers
Laser micromachining
Conclusion
Chirped-pulse-amplification
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Fraunhofer IOF
amplifier
stretched pulseamplified pulse
stretcher compressor
short
pulse
amplifiedshort pulse
D. Strickland and G. Mourou, Compression of amplified optical pulses, Opt. Comm. 56, 3, 219 (1985).
Chirped-pulse-amplification
CPA-fiber amplifier
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Fraunhofer IOF
isolator
Isolator
diode laser
dielectric gratingcompressor
fs-oscillator
preamplifier
diode laser
Yb-dopedpower amplifier
2 W, 10 MHz350 fs, 1030 nm
temporal scalinglarger stretching
factor
spacial scalingincreased mode-field-area
dielectric gratingstretcher
AOM
80 MHz...10 kHz
output
CPA-fiber amplifier
CPA-fiber amplifier high average power system
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Fraunhofer IOF
820 W average power @ 650 fs
15 MW peak power (78 MHz rep.-rate)
CPA fiber amplifier high average power system
CPA-fiber amplifier high energy system
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Fraunhofer IOF
autocorrelation trace
0 50 100 150 200 2500
20
40
60
80
100
C o m p r e s s e d o u
t p u t p o w e r
[ W ]
Launched pump power [W]
slope efficiency = 46%
100 W compressed @ 100 kHz1 mJ pulse energy
compressed output
CPA fiber amplifier high energy system
-10 -5 0 5 100.0
0.2
0.4
0.6
0.8
1.0
AC = 1.23 ps
AC = 1.2 ps
AC = 0.93 ps
S H I n t e n s i t y
[ a . u . ]
Time delay [ps]
200/80 Rod-type PCF
Fiber lasers and amplifiers: peak power
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Fraunhofer IOF
1992 1994 1996 1998 2000 2002 2004 2006 20081k
10k
100k
1M
10M
100M
1G
10G
Uni Jena IMRAUni Bordeaux
Cornell Uni P u
l s e p e a k p o w e r
[ W ]
year
evolution of peak pulse of high repetition rate ultrafast fiber laser
Fiber lasers and amplifiers: peak power
Outline
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Fraunhofer IOF
Fiber lasers basic principles
High power, high energy nanosecond fiber amplifiers
High power femtosecond fiber amplifiers
Laser micromachining
Conclusion
Interaction of intense laser radiation with solids
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Fraunhofer IOF
long pulses ( > 10 ps) ultrashort pulses ( < 1 ps)
Skin-depth ~ 10 nmv
expansion~ v
sound~ 10 5 - 10 7 cm/s
xplasma (100 fs) ~ 1 - 10 nmxplasma (10 ns) ~ 100 - 1000 m
Plasma Shielding!
Plasma expansion
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Fraunhofer IOF
Streak camera image of an expanding laser produced tungsten plasma
laser pulseplasma
frontv
expans= 510 6 cm/s
expanding plasma
p
Time scales in ultra short pulse machining
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Fraunhofer IOF
fs ps ns s
energydeposition
electronicthermalization
electron latticeenergy exchange
ablation
max. rep.-rate: 100 kHz 1 MHz
p g
Precision drillings in steel
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Fraunhofer IOF
entrance
exit
material: steelthickness: 200 mpulse duration: 170 fsfluence: 2.5 J/cm
high aspect ratio!
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Polarization trepanning
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Fraunhofer IOF
linearly polarized
material: steelthickness: s = 1.0 mm
diffractive opticsenvironment: air
rear surface
Micro-drilling of stainless steel
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Fraunhofer IOF
entrance
hole diameter: 50 mmaterial: 1.4301thickness: 0.2 mm
combination of DOE andlens:
DOE : ring-profilelens: f = 40 mm
pulse duration: 120 fs
pulse energy: 600 Jrep. rate: 1 kHz
process gas: Helium
exit
array
detail detail
arraydrillings parameters
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Precision drillings in steel
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Fraunhofer IOF
fuel injection nozzlesdetails of fs-drilled hole
exit replica
entry
material: steelpulse duration: 120 fsfocal length: 80 mm
Analytical solution of the cooling cycle after a single pulse for t
Heat accumulation
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Fraunhofer IOF
( )21
20
4 / Dt t
w I T l a
=
Ia : absorbed laser-light intensityW 0 : beam waist l : pulse duration : thermal conductivityD : heat diffusivity : repetition rateE
p :Pulse energy
N.P. MELT = T M / T
Minimum number of pulses to reach the melting temperature:
Analytical solution of the cooling cycle after a single pulse for t l
t = 1/
25234 /
/
=
Pl
M MELT
E A
T D NP
D. Buerle, Laser Processing and Chemistry (1996)
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Percussion drilling of stainless steel
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Fraunhofer IOF
: 1030 nmpulse width: 800 fs
pulse energy: 70 J
focal length: 25 mmfluence: 33 J/cm 2
0 100 200 300 400 500 600 700 800 900
0.01
0.1
1
Repetition Rate (kHz)
B r e a
k t h r o u g
h T i m e ( s
)
Fe/Cr18Ni10
thickness0.5 mm1 mm
Laser trepanning @ 510 kHz
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Fraunhofer IOF
laser fluence: ~ 1 J/cm 2
trepanning radius: 75 mrotating speed: > 100 rounds/sbreakthrough time: 800 ms
stainless steel (Fe/Cr18Ni10),thickness: 0.5 mm
Outline
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Fraunhofer IOF
Fiber lasers basic principles
High power, high energy nanosecond fiber amplifiers
High power femtosecond fiber amplifiers
Laser micromachining
Conclusion
Conclusion
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Fraunhofer IOF
short pulse fiber lasers and amplifiers
Pulse-energy: mJ-range
Peak power: GW-range
Average power: kW-range
novel applications in science and industry
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Fraunhofer IOF
FhG IOFFhG IOF
FSUFSU -- JenaJena IAPIAP