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Institute of Technical Physics
Folie 1
High Power Thin Disk Lasers Dr. Adolf Giesen German Aerospace Center Institute of Technical Physics
Institute of Technical Physics
Folie 2
Research Topics - Institute of Technical Physics
Laser sources and nonlinear optics
Speiser
Atm. propagation and target effects
Handke
Studies and Concepts
Eckel
Beam control and optical diagnostics
Riede
„Stand off“ Detection
Handke
Pulse laser NLO
Trials, spectroscopy, data processing
System studies, risk reduction
(Receiver) Optics
Long range laser effector
Speiser High power laser
Propagation and target effects
Scenarios, system studies
Beam control
Laser propulsion Eckel
(Pulse) Laser Mission studies, system concepts
Transmitter optics beam control
Opt. reconnaissance (space situational awareness)
Riede
Pulse laser Atmospheric data,
trials Threat analysis, system studies
Telescope, beam control
Target effects
Institute of Technical Physics
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Outline
Thin Disk laser concept
State of the art (commercial & laboratory)
Pulsed Thin Disk lasers – influence of ASE
Power scalability & high brightness
High power laser design
Eye-safe Thin Disk laser
Scaling limits
Summary
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Core idea: thin active material, one face cooled, used as active mirror thickness 0.1 – 1 mm, diameter 5 – 45 mm Heat flow parallel to laser beam Minimized thermal lens High output power and high efficiency simultaneously Power / energy scaling by scaling of pump spot area (power / energy densities and temperatures constant) variety of active materials
Thin Disk laser concept
Lase
r
Hea
tre
mov
al
Thin Disk
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Pump source brightness requirements: constant for power scaling (~80 kW cm-2 sr-1 for 5 kW/cm2 with 24 pump passes )* => low costs
Decoupling of pump absorption and laser reabsorption significantly increases performance of quasi-3-level materials like Yb:YAG
Small pump absorption in single pass Simple setup to re-use not absorbed pump power With 1 parabolic mirror and 5 plane mirrors 16 – 32 (44) pump beam passes realized
Thin Disk laser concept
* S. Erhard, Pumpoptiken und Resonatoren f. den Scheibenlaser, PhD Thesis, 2002
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Thin Disk laser – technical realization
new design for high-power Disk module > 30 kW pump power, suitable for vacuum Development of DLR-TP and industrial partner (D+G)
medium power disk (> 500 W) low power Thin Disk pump module
medium power Thin Disk pump module in operation
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State of the art - Commercial systems
High power, multimode 1 kW, 1 disk, 2 mm mrad (M² ~ 6) 4 kW – 16 kW, 1 – 4 disks, < 8 mm mrad (M² ~ 24)
Pulsed
Mode-locked oscillator, 80 W average power, 800 fs Regenerative amplifier, 40 µJ, 100 kHz, 400 fs Cavity dumped, 750 W average power, 80 mJ, 30 ns
Small systems 3 W @ 532 nm, 105.7 mm x 62 mm x 24 mm (without DC power supply)
TRUMPF Kurzzeichen - 25.04.2007 Titel der Präsentation © TRUMPF - vertraulich 8
Enhanced efficiency with 44-pass pump cavity
Jenoptik Laser GmbH customer day July 1st, 2011
JenLas® D2.fsregenerative thin disk laser
E > 40 µJ @ 100 kHzt < 400 fsf 200 kHz≤M² 1.25≤
Yb:KYW / YAG
VaryDisk
200fs, 4nJ, 100mW, 40MHz
disk module
HR
Polarizer
Pockels cell
HR separation input/output
seed laser
compressor
amplifier
200µJ 50W 350fs 1MHz
modulator
Different pulse durations out of one resonator No further alignment for applications
a product of Dausinger + Giesen GmbH
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State of the art – Lab results
500 W, M² < 1.1
(A. Killi et. al. „The broad applicability of the Disk Laser principle – from CW to ps“, in Solid State Lasers XVIII: Technology and Devices, Proc. SPIE Vol 7193 (SPIE 2009))
27 kW, about 10 disks in an unstable resonator – “excellent beam quality”
(P. Avizonis et. al. “PHYSICS OF HIGH PERFORMANCE Yb:YAG THIN DISK LASERS”, CLEO 2009)
380 mJ, 8 ns, 88 W average power, M² < 1.3 (A. Killi et. al. „The broad applicability of the Disk Laser principle – from CW to ps“, in Solid State Lasers XVIII: Technology and Devices, Proc. SPIE Vol 7193 (SPIE 2009))
CPA-System with 188 mJ, 100 Hz, M² < 1.1, compressible < 2 ps, amplification to ~ 300 mJ demonstrated
(J. Tümmler et. al. “High Repetition Rate Diode Pumped CPA Thin Disk Laser of the Joule Class”, CLEO Europe 2009)
Thin Disk Amplifier Chain
Multipass Amplifier – Results
0 50 100 150 200 2500
100
200
300
400
500
600
Out
put E
nerg
y [m
J]
Input Energy [mJ] (Output PRA)
multipass output after 4 double passes – pump power 6 kW
Emax = 545 mJ Emean = 517 mJ +/- 1.8%
Max-Born-Institut
Disk parameter: diameter: 17 mm thickness: 500 µm doping level: 7%
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Time resolved model: spatial pump absorption spatial inversion ASE in the disk average temperature calculations with 1 ms pump pulse, 10% heat generation here: 10% duty cycle
=> Calculate gain /
max. stored energy / efficiency
4.5% Yb:YAG, thickness 600 µm, pump power 16 kW, pump spot radius 9.8 mm
0 500 1000 15000
10
20
30
40
50
60
doub
le p
ass
gain
[ %
]
t [ µs ]
gain without ASE with ASE
0
5
10
15
20
25
30
35
40
45efficiency
η ex [
% ]
Amplified spontaneous emission (ASE) results of time resolver numerical model
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Geomtrical Multipass amplifier Numerical calculations & experimental results
0 20 40 60 80 100 120 140 160 180 2000
100
200
300
400
500
600
Experiment Calculation
7% Yb:YAG, 500 µm, 5.5 mm, 3.5 kW, 8 reflektions / V-passes
pulse
ene
rgy
[ mJ
]
seed energy [ mJ ]
Low duty cycle, low pump power
Comparison with actual results from Max Born Institute
high duty cycle, high pump power
Possible concept for multipass amplifier
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Actual high energy / high peak power projects
Max Born Institute Yb:YAG Thin Disk CPA system (regenerative amplifier + several multipass stages), goal: 1 J, 5 ps, 100 Hz (1,6 J before compressor, ns), 550 mJ reached
MPQ Garching Yb:YAG Thin Disk CPA system (regenerative amplifier), 28 mJ, 3 kHz, 1.6 ps running
extension with multipass amplifier stages planned (up to 10 J discussed)
DLR-TP Yb:YAG Thin Disk system (regenerative amplifier + 1 multipass stage), goal: 1 J, 100 ps – 10 ns, 1 kHz for laser ranging of space debris
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High-Brightness Oscillator using Neutral Gain Modules V-shaped resonator with 2 Relay NGMs and AO
0 1 2 3 4 50
250
500
750
1000
1250
1500
outp
ut p
ower
Pou
t (W
)
pump power Pp (kW)
0,1
0,2
0,3
optic
al e
fficie
ncy η
M2x,y = 2.43, 2.91
Pout = 1534 W
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Concept of Neutral Gain Modules Relay NGM with optional OPD compensation
1
10
...AO
......
Σ
Σ
kj SSS
−
=101
totDtot D
M
+
== −101
tot
1Dcorr tot D
MM
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Power scalability & Brightness
5.3 kW out of one disk / 20 kW with four disks
Courtesy TRUMPF Laser Schramberg
extracted volume power density > 600 kW/cm³
0 5 10 15 20 25 30 35 400
5
10
15
20
lase
r pow
er [
kW ]
pump power [ kW ]
1 disk 2 disks 4 disks
0 1 2 3 4 5 6 70,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
outp
ut p
ower
Pou
t (kW
)
pump power Pp (kW)
0
10
20
30
40
50
60
70Mx,y
2 = 6.6, 6.3
opt
ical e
fficie
ncy
(%)
Mx,y2 = 5.2, 5.1
Two confocal neutral gain modules* (4 disks) in V-shaped resonator
3 kW laser power, M² ≈ 6.5
* J. Mende et. al., Concept of Neutral Gain Modules for Power Scaling of Thin-Disc Lasers, Applied Physics B, 97 (2), 2009
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3-stage MOPA for 10 kW
Stable resonator
6 kW pump power
2 kW output power
6 kW pump power
11.3 mm pump diam.
20 passes
5 kW output power
6 kW pump power
11.3 mm pump diam.
8 passes
7.5 kW output power
6 kW pump power
11.3 mm pump diam.
6 passes
10 kW output power
Pump spot diameter, pump power and power densities similar to actual commercially used systems!
multipass amplifier
master oscillator 14% Isat
multipass amplifier
multipass amplifier
52% Isat 33% Isat
new design for high-power Disk module 30 kW pump power, suitable for vacuum Development of DLR-TP and industrial partner (D+G)
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MOPA for 200 kW
Low power oscillator (~ 2-3 kW laser power)
Pre-Amplifier with pump & beam size adaption 1 low-power amplifier (~ 6 kW pump power) with high number of multipasses 3 mid power amplifiers with high number of multipasses
12 stage Power Amplifier with constant beam size & low number of multipasses
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Power amplifier
0
50
100
150
200
2 passes4 passes
Lase
r pow
er [
kW ]
38 kW pre-amplifier 41 kW pre-amplifier 43 kW pre-amplifier 45 kW pre-amplifier
29 kW pump power / Modultotal pump power 348 kW 4.5 cm² pump spot
6 passes
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Preamp + Power amplifier
0 1 2 3 4 5 60
50
100
150
200
250
Oscillator power [ kW ]
Lase
r pow
er [
kW ]
power
45
46
47
48
49
50
51
52
53
54
55
efficiency
Effic
ienc
y [ %
]
402 kW total pump power
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New laser materials for the 2 – 3 µm wavelength range
Ho:YAG Thin Disk laser Pump source 50 W Tm-fiberlaser Laser output power only limited by available pump power
0 10 20 30 40 500
2
4
6
8
10
12
14
16 disk laser power efficiency
1.908 µm fiber laser pump power (W)
2.09
µm
disk
lase
r pow
er (W
)
0
10
20
30
40
efficiency (%)
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New laser materials for the 2 – 3 µm wavelength range
Ho:YAG Thin Disk laser First low-power experiments More than 20 nm tuning range Suitable for Standoff / LIDAR applications High power operation possible
2,07 2,08 2,09 2,10 2,110,00,20,40,60,81,01,21,4 Emission cross section
Output power
Wavelength [µm]Emis
sion
cro
ss s
ectio
n [1
0-20 c
m2 ]
0,0
0,2
0,4
0,6
0,8
1,0
1,2
Out
put p
ower
[W]
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Scaling limits
Use “analytical ray tracing” with some simplifications / idealizations and some rough estimations
Scaling strongly influenced by “thermal load parameter” / “thermal shock parameter” Cth and internal loss Lint
570 kW with Lint=1%, 22 MW with Lint=0.25%, efficiency about 10%
1 MW with Lint=0.25%, efficiency about 50% 400 J with Lint=1% Would benefit from materials with higher thermal conductivity and less heat generation (like Yb:Lu2O3 ) or reduced duty cycle
D. Kouznetsov et. al. Surface loss limit of the power scaling of a thin-disk laser, J. Opt. Soc. Am. B 23, 1074 (2006) J. Speiser, Scaling of Thin Disk Lasers - Influence of Amplified Spontaneous Emission, JOSA B 26 (2009)
− g
hr
hr pp
ASE2
exp~ ττ
3int
2max, ~
−⋅LCP thout
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Outlook High power Thin Disk lasers several 100 kW based on actual technology (coating, disk diameter) feasible with good beam quality and high efficiency
High energy Thin Disk lasers ~ 5 - 10 J based on actual technology (coating, disk diameter) under construction, scaling towards 100 J feasible
Eye-safe Thin Disk lasers High power operation possible
Pulse duration nearly arbitrary with MOPA (limited by round-trip time of first amplifier; sub-ps need suitable laser materials)
Further energy scaling (Coherent) coupling of several amplifier chains ~ kJ possible
High Power Thin Disk Lasers���Dr. Adolf Giesen���German Aerospace Center�Institute of Technical PhysicsResearch Topics - Institute of Technical PhysicsOutlineThin Disk laser concept�Thin Disk laser concept�Thin Disk laser – technical realizationState of the art - Commercial systems Enhanced efficiency with 44-pass pump cavityFoliennummer 9Foliennummer 10State of the art – Lab resultsFoliennummer 12Foliennummer 13Geomtrical Multipass amplifier�Numerical calculations & experimental results Actual high energy / high peak power projectsHigh-Brightness Oscillator using Neutral Gain Modules �V-shaped resonator with 2 Relay NGMs and AOConcept of Neutral Gain Modules �Relay NGM with optional OPD compensationPower scalability & Brightness3-stage MOPA for 10 kWMOPA for 200 kWPower amplifierPreamp + Power amplifierNew laser materials for the �2 – 3 µm wavelength range �New laser materials for the �2 – 3 µm wavelength rangeScaling limitsOutlook