Jens Limpert - Swissphotonics :: Home
Transcript of Jens Limpert - Swissphotonics :: Home
Jens [email protected]
+49 (0) 36 41. 947 811 +49 (0) 36 41. 947 802
High power fiber lasers and amplifiers
Jens Limpert
Friedrich-Schiller University Jena, Institute of Applied Physics, Jena, Germanyand
Fraunhofer Institut of Applied Optics and Precission Engeniering, Jena, Germany
Outline of the talk
Properties of Fiber Lasers
Advanced Fiber Designs
Selected Experiments of High Power Fiber Lasers
Conclusion and Outlook
High power fiber lasers and amplifiers
rod
disk slab fiber
Solid-State Laser Concepts
power dependent thermal lensing and thermal stress-induced birefringence
reduced thermo-optical distortions
347 -- 352342 -- 347337 -- 342333 -- 337328 -- 333324 -- 328319 -- 324315 -- 319310 -- 315288
temperature [K]
Double-clad fiber laser
active corecladding
pumplight
laser radiation
mirror
mirror
inner cladding (pump core)
outer cladding
active core
laser radiation
refractive index profile
n
active corecladding
pumplight
laser radiation
mirror
mirror
Properties of Rare-Earth-Doped Fibers
• no or reduced free space propagation• immune against thermo-optical problems• excellent beam quality• high gain• efficient, diode-pumped operation
Power evolution of single-mode fiber lasers
1992 1994 1996 1998 2000 2002 2004 20060
500
1000
1500
2000
2500
3000
3500
2500 W
3000 W
2000 W
1530 W1360 W
1300 W800 W
600 W
135 W200 W
150 W170 W
485 W
110 W9,2 W5 W 30 W
Con
tinuo
us-w
ave
outp
ut p
ower
[W]
Year
V. Fomin et al, “3 kW Yb fibre lasers with a single-mode output,” InternationalSymposium on High Power Fiber Lasers and their applications (2006)
1050 1075 1100 1125 1150 1175 1200
Stokes-SignalLaser
Ausgangsleistung 100 W 110 W 120 W
Inte
nsitä
t [w
.E.]
Wellenlänge [nm]
Performance-limiting effectsEnd-facet damage
Thermal effects
Non-linear effects
Available pump power
Source: www.specialtyphotonics.com
1050 1075 1100 1125 1150 1175 1200
Stokes-SignalLaser
Ausgangsleistung 100 W 110 W 120 W
Inte
nsitä
t [w
.E.]
Wellenlänge [nm]
Performance-limiting effectsEnd-facet damage
Thermal effects
Non-linear effects
Available pump power
Source: www.specialtyphotonics.com
effR
effSRSthreshold Lg
AconstP
⋅
⋅=
.
Photonic Crystal FibersDouble clad fibers
Polymer coating
Active core
Pump cladding
•guiding properties of the core
•guiding of the pump light
Microstructured Fiber Step-index Fiber
Δn ~ 1·10-4
NA ~ 0.02Δn ~ 1·10-3
NA ~ 0.06
significantly larger single-mode core possible
Index control of doped fiber cores
n
r
ncore
nClad
0 a
neff-01
n
r
ncore
nClad
0 a
neff-01
n
r
ncore
0
neffclad
neff-01
405.22 22 ≤−⋅= cladcore nnaVλπ
Yb-doped corePump core area
Coating
0 200 400 600 800 1000 1200 1400 1600 1800 20000,0
0,2
0,4
0,6
0,8
1,0
350 nm 380 nm 400 nm
NA
Bridge width [nm]
25 µm
380 nm
The air-cladding region
high numerical aperture inner cladding no radiation has contact to coating material
1.5 mm outercladding
pump core(200 µm)
active core(80 µm)
air-clad 8 µm core
„rod-type“ fiber: 30 dB/m Pumplichtabsorption, 71 µm Modenfelddurchmesser, M2 ~ 1.2
“rod-type” photonic crystal fiber
Limpert et. al., "High-power rod-type photonic crystal fiber laser," Opt. Express 13, 1055-1058 (2005)
Rod-type photonic crystal fiber laser
0 50 100 150 200 250 300 350 400 4500
50
100
150
200
250
300
350slope efficiency ~ 78%
Out
put p
ower
[W]
Launched pump power [W]
320 W continuous-wave, >10 mJ ns-pulses extracted
Design freedom to tailor optical, mechanical and thermo-optical properties
Advantages of PCF
•higher index control•larger SM cores
•shorter fibers possible (0.5 m)•comparable heat dissipation
•intrinsically polarizing without drawbacks
Rare-earth doped photonic crystal fibers
fs source
Fiber
Fiber laser systems
fiber integrated mirror, e.g. fiber bragg grating
Fiber
Pump light coupling, e.g. tapered fiber bundles
all fiber laserCW, Q-switched
Fiber
low power light source
single pass amplifiers advanced fiber amplifiers
Pump(R=1) (R<1)
saturableabsorber
dispersioncompensation
activemedium
ultra-short fiber oscillators
Properties of Fiber Lasers
Advanced Fiber Designs
Selected Experiments of High Power Fiber Lasers
Conclusion and Outlook
High power continuous-wave fiber laser
0 500 1000 1500 2000 2500 3000 3500 40000
250500750
100012501500175020002250250027503000
slope efficiency of 75 % measurement
Out
put p
ower
[W]
launched pump power [W]
•fiber length 15 m, forced air-cooling
•two side pump coupling of 2 kW
•fiber temperature max. 120°C
•beam quality M² < 1.4 at 2 kW
•max. 2.53 kW laser output
75% slope efficiency (below 1.5 kW, above wavelength drift of pump diode)
Scaling approach: Incoherent Combining
transmission grating
Λ= 800 nm)(cos LittΘ⋅Λ
Δ=ΔΘ
λ
(in near and far field)
Polarizing PCF, 1.5 m, 40 µm core
153 W
Combining-efficiency 95 %Degree of Polarization 98%
Scalable while maintaining beam quality
S. Klingebiel,F. Röser,B. Ortac, J. Limpert, A. Tünnermann, ”Spectral beam combining of Yb-doped fiber lasers with high efficiency,”JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 24 (8): 1716-1720 (2007)
Combining of pulsed fiber lasers
two beams (ΔΤ ~ 10ns):
Inte
nsity
[a.u
]
Time [50 ns/Div]
M²x =1.17M²y =1.10
M²x =1.22M²y =1.13
M²x =1.17M²y =1.18
SPIRICONTM M2 measurementscaling of MW peak power pulsed fiber sources beyond self-focusing limit of 4 MW
Q-switching of fiber lasers
AOM air-cooledHR @ > 1010 nmHT @ < 990 nm
Q-switching elementHR @ > 1010 nm
rod-type fiber
output
Yb-dopedHT @ < 990 nm
diode @ 976 nm
pump PCF
R = 0.08
end caps on
Microscope image of the rod-type photonic crystal fiberand close-up to the inner cladding and core region.
Fiber parameter:
outer diameter: up to 2 mm60 µm Yb-doped core, Aeff ~ 2000 µm2,
180 µm (NA ~ 0.6) inner cladding30 dB/m pump absorption @ 976 nm,
(0.5 m absorption length)
0 20 40 60 80 100
4
6
8
10
Aver
age
outp
ut p
ower
[W]
Repetition rate [kHz]
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Pul
se e
nerg
y [m
J]
output characteristics @ 100 kHz
0 50 100 1500
25
50
75
100
Ave
rage
out
put p
ower
[W]
Launched pump power [W]
0
20
40
60
80
100
120
Pul
se d
urat
ion
[ns]up to 100 W
down to 12 ns
output characteristics vs. rep. rate
pulse @ 2.5 mJ energy
-20 -10 0 10 20 30 40 500,0
0,2
0,4
0,6
0,8
1,0
Δτ = 8 ns
Inte
nsity
[a.u
.]
Time [ns]
Q-switching of fiber lasers
O. Schmidt, J. Rothhardt, F. Röser, S. Linke, T. Schreiber, K. Rademaker, J. Limpert, S. Ermeneux, P. Yvernault, F. Salin, A. Tünnermann, “Millijoule pulse energy Q-switched short-length fiber laser,” Optics letters Vol.32, No.11, 1551-1553, 2007
Quasi-monolithic, passively Q-switched microchip laser
808nm, 0.5W100µm, 0,22NA
f=30mm f=20mm a) b) c)
AR@808nm, HR@1064nm
a) 0.2mm, 3% doped Nd:YVO4, AR@808nm, T=10% @ 1064nm
b) Spin on glass glue,c) SESAM, ΔR=20%,
TR= 320ps,
-Unmatched simplicity
-No moving parts in theresonator
-Simple gluing technique
-Spin on glass glue*high dielectric strength*high transparency
•1µJ, 50ps, 40kHz•0.5µJ, 110ps, 170kHz
Current production costs:~300€
3mm
D. Nodop, J. Limpert, R. Hohmuth, W. Richter, M. Guina, and A. Tünnermann,"High-pulse-energy passively Q-switched quasi-monolithic microchip lasers
operating in the sub-100-ps pulse regime," Opt. Lett. 32, 2115-2117 (2007)
Fiber based amplification of ps-µchip lasers
Pump diode
amplified signal
low costmicro-chip
laser
Isolator
60 ps, 0.75 µJ, 50 kHz
60 ps, 80 µJ, 50 kHz peak power: 1.33 MW
micromachining
35 µm, 1.5 m
Pump(R=1) (R<1)
ultra-shortpulsed laser
SA
DC
AM
•active medium (AM)-e.g. Yb-doped fiber
•saturable absorber (SA)-favours pulse against noise background-initiates mode-locking
•dispersion compensation (DC)- keeps the pulse short during roundtrip
Dispers
ion
Nonlinea
rity
gain
loss
Theory: dissipative, nonlinear system:
Ultra-short pulse generation
High-energy femtosecond fiber laser
Pump diode975 nm
OutputOptical IsolatorM1
HR
4λ
M2
Yb-doped rod-type fiberL1 L2 L3
SAM L4
HR
HR
HR
Total cavity dispersion : + 0.012 ps2
Repetition rate : 10.18 MHz
Modulation depth 30%Fast relaxation time 200 fsSlow relaxation time 500 fs
dispersion compensation free
B. Ortaç, O. Schmidt, T. Schreiber, J. Limpert, A. Tünnermann, A. Hideur,“High-energy femtosecond Yb-doped dispersion compensation free fiber laser,” Optics Express, vol. 15, pp. 10725– 10732, 2007.
-20 -10 0 10 200.0
0.2
0.4
0.6
0.8
1.0
In
tens
ity (a
. u.)
Delay time (ps)
Autocorrelation trace
• Output pulse duration = 4 ps
-6 -4 -2 0 2 4 60.0
0.2
0.4
0.6
0.8
1.0
In
tens
ity (a
. u.)
Delay time (ps)
Extra-cavity compression
• Compressed pulse duration = 400 fs
Compression efficiency: 75 %
Energy per pulse: 200 nJ
Peak power: 500 kW
Average output power: 2.7 W
Energy per pulse: 265 nJ
Single pulse characterization:
High-energy femtosecond fiber laser - Results
Optical Spectrum
• Spectral bandwidth = 8.4 nm
-6 -4 -2 0 2 4 60.0
0.2
0.4
0.6
0.8
1.0
In
tens
ity (a
. u.)
Delay time (ps)
Extra-cavity compression
• Compressed pulse duration = 400 fs
Compression efficiency: 75 %
Energy per pulse: 200 nJ
Peak power: 500 kW
Average output power: 2.7 W
Energy per pulse: 265 nJ
Single pulse characterization:
1010 1020 1030 1040 1050
10-3
10-2
10-1
100
Inte
nsity
(a. u
.)
Wavelength (nm)
High-energy femtosecond fiber laser - Results
Ultra-short pulse fiber amplification systemsHigher average power
Higher pulse energy Higher repetition rate
1 10 100 1000
10
100
1000
10000
100 W
10 W1 W
100 mW
Puls
e en
ergy
[µJ]
repetition rate [kHz]
Higher average power
Higher pulse energy Higher repetition rate
1 10 100 1000
10
100
1000
10000
100 W
10 W1 W
100 mW
Puls
e en
ergy
[µJ]
repetition rate [kHz]
fiber-basedsystems*
* Röser et. al., „Millijoule pulse energy high repetition rate femtosecond fiber chirped-pulse amplification system,“ Opt. Lett. 32, 3495 (2007)* Röser et. al., „90 W average power 100 μJ energy femtosecond fiber chirped-pulse amplification system,” Opt. Lett. 32, 2230 (2007)
Ultra-short pulse fiber amplification systems
-4 -2 0 2 40,0
0,2
0,4
0,6
0,8
1,0 B = 0 B = 0.6 B = 8 B = 16
SHG
inte
nsity
[a.u
.]
Time delay [ps]
( )∫ ⋅⋅
=L
dzzInB0
22λπ
Accumulated nonlinear phase (B-integral):
Influence of self-phase modulation (SPM)
Reduction of pulse quality
Simulated autocorrelation traces
( ) ( ) zTzATzSPMNL
2,, γφ =
Nonlinear phase:
Chirped Pulse Amplification (CPA)
reduced pulse peak power during amplification
mode-locked laser amplifier grating compressorgrating stretcher
D. Strickland and G. Mourou, “Compression of amplified optical pulses,”Opt. Comm. 56, 3, 219 (1985).
reduced nonlinearityenhanced damage threshold
Yb:KGW oscillator Stretcher -Compressor -
Unit
AOMPre-amplifier
Main amplifier
ISO
Output
State of the art FCPA System
Schematic Setup
Yb:KGW oscillator9.7 MHz, 1.6 W, 400 fs , 1030 nm
Stretcher -Compressor -
Unit
AOM
ISO
Output
State of the art FCPA System
Schematic Setup
Pre-amplifier
Main amplifier
Yb:KGW oscillator9.7 MHz, 1.6 W, 400 fs , 1030 nm
Stretcher -Compressor -
Unit1740 l/mm
dielectric gratings
AOM
ISO
Output
State of the art FCPA System
Schematic Setup
Pre-amplifier
Main amplifier
Yb:KGW oscillator9.7 MHz, 1.6 W, 400 fs , 1030 nm
Stretcher -Compressor -
Unit1740 l/mm
dielectric gratings
AOM
Pre -amplifier40 µm core PCF, 1.2 m
Main amplifier80 µm core PCF, 1.2 m
ISO
Output
State of the art FCPA System
Schematic Setup
1.5 mm outercladding
pump core(200 µm)
active core(80 µm)
air-clad
Rod-type photonic crystal fiber
High pump light absorption (30dB/m) -> short fiber length+ large mode area ( >100x of standard fiber) -> ultralow Nonlinearity
Limpert et. al., "High-power rod-type photonic crystal fiber laser," Opt. Express 13, 1055-1058 (2005)
State of the art FCPA System
8 µm core
200/80 Rod-type PCF, 1.2m length
MFD = 71 µm-> MFA ~ 4000 µm2
Near field image
State of the art FCPA System
M2x = 1.17 , M2
y = 1.26(Spiricon™, 4σ method)
Beam quality-measurement
Yb:KGW oscillator9.7 MHz, 1.6 W, 400 fs , 1030 nm
Stretcher -Compressor -
Unit1740 l/mm
dielectric gratings
AOM
Pre -amplifier40 µm core PCF, 1.2 m
Main amplifier80 µm core PCF, 1.2 m
ISO
Output
State of the art FCPA System
Schematic Setup
• multilayer dielectric reflection gratings – average power scalable• 70% compressor throughput efficiency
0 50 100 150 200 2500
20
40
60
80
100
Com
pres
sed
outp
ut p
ower
[W]
Launched pump power [W]
slope efficiency = 46%
100 W compressed @ 200 kHz-> 0.5 mJ pulse energy
Output characteristics
State of the art FCPA System
50 W compressed @ 50 kHz-> 1 mJ pulse energy
0 50 100 150 2000
10
20
30
40
50
Com
pres
sed
outp
ut p
ower
[W]
Launched pump power [W]
total slope efficiency = 25%
1020 1030 1040 1050
-80
-70
-60
-50
-40
-30
-20
1000 1020 1040 1060 1080
-80
-60
-40
Inte
nsity
, log
sca
le [a
.u.]
Wavelength [nm]
Wavelength [nm]
1020 1030 1040 1050-80
-70
-60
-50
-40
-30
-20
1000 1020 1040 1060 1080
-80
-70
-60
-50
-40
-30
Inte
nsity
, log
sca
le [a
.u.]
Wavelength [nm]
Wavelength [nm]
State of the art FCPA System
Spectrum @ highest power
ASE supression better than 30 dBExtended measurement shows no sign of Stimulated Raman Scattering
(1st stokes expected at 1080nm)
Spectrum @ highest pulse energy
-10 -5 0 5 100.0
0.2
0.4
0.6
0.8
1.0
ΔτAC = 1.23 ps ΔτAC = 1.2 ps ΔτAC = 0.93 ps
SH In
tens
ity [a
.u.]
Time delay [ps]
At low pulse energy
200 kHz / 500 µJ(B-Integral 4.7)
50 kHz / 1 mJ(B-Integral 7)
Autocorrelation
1mJ, 800 fs => pulse peak power ~ 1 GW!
State of the art FCPA System
0 200 400 600 800 1000 12000
100
200
300
400
500
600
700
800
slope efficiency 66%
Out
put p
ower
[W]
Launched pump power [W]
Average power scalability of main amplifier
710 W max. output (pump power limited)
570 W/m with no thermal degradation(passively cooled)
diode laser80 µm core Rod-type PCF1.2 m Lengthdiode laser DM DM
HR R=10%Schematic Setup cw cavity
1 kW, 1 MHz, 1 mJ, sub-1 ps !
75 msbreakthrough time
106 rounds/srotating speed
75 µmtrepanning radius
Copper (Cu 99.9%)
Thickness: 0.5 mm
Rep.rate.: 975 kHz
Pulse Energy : 70 μJ
Focal length: 80mm
Fluence: ~ 2.32 J/cm2
Number of rounds: 50
Laser trepanning with high average power on copper
Conclusion and outlook
Success story is based on …RE-doped fibers are a power scalable solid-state laser concept !
significant progress in fiber manufacturing technologyrecent developments of reliable high power all solid-state pump sources
Outstanding performance in a variety of operation regimescontinuous-wave: >10 kW diffraction-limited
ultra-short pulse: >1 kW, 1 MHz, 1 mJ, sub-1 ps
RE-doped fibers are good for …