High Power Thin Disk Lasers Dr. Adolf Giesen · 2013. 12. 12. · (A. Killi et. al. „The broad applicability of the Disk Laser principle – from CW to ps“, in Solid State Lasers

Institute of Technical Physics

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High Power Thin Disk Lasers Dr. Adolf Giesen German Aerospace Center Institute of Technical Physics


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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


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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


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


* 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

Documents

High Power Thin Disk Lasers Dr. Adolf Giesen · 2013. 12. 12. · (A. Killi et. al. „The broad applicability of the Disk Laser principle – from CW to ps“, in Solid State Lasers