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ILE Osaka University
High-peak power laser systemused in Yb doped LMA fiber
Institute of Laser Engineering, Osaka University, Suita, Osaka, Japan
YOSHIDA Hidetsugu, TSUBAKIMOTO Koji, FUJITA Hisanori, NAKATSUKA Masahiro, MIYANAGA Noriaki, IZAWA Yasukazu
2007 International Extreme Ultraviolet Lithography (EUVL) Symposium29 - 31 October, 2007Sapporo Convention Center,Sapporo, JAPAN
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ILE Osaka University
Generation of optional pulse shape by Yb doped fiber laser system for EUV lithography laser (1) Introduction(2) Development of optional electrical pulse circuit.(3) Generation of optional laser pulse.(4) PM-Yb Large Mode Area fiber amplifier.(5) Conclusion.
Contents
Single-modeYb oscillator
LN modulator
Electrical pulse shape
PM-Yb:SMF PM-Yb:LMA-F
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Optional pulse generation by fiber couple LN-modulator
CW laser
LN-EO modulator
Electric pulse generator
PC
< Pulse stacker>
< EO first pockels cell>
High voltage(3-4kV)
Low voltageOptional pulse shapeStable
< Fiber couple LN modulator >
P.C.
1-2V
H. V. pulser
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1064nmFBG-FL
1030 nmFBG-FL
1053 nmFBG-FL
1080 nmFBG-FL
LN Modulator
980 nm LD325 mW
Powermonitor
980 nm LD200 mW
FBG FBG
Temp. control.
Yb:fiber
Yb:fiberYb:fiber
980 nm LD325 mW
980 nm LD325 mW
980 nm LD325 mW
Powermonitor
20 nsOutput 15.6nJ @5 kHz
13 GHz100-ps step
Pulse shape control
20m
20m 20m
1µW
200pJ
100µW
20nJ
G=100
G=200
Front-end laser system of single-mode andpolarization-maintain Yb fiber laser
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400ps FWHM
250ps
500ps
CH1
CH 2
CH 3
9750 ps CH40
Trigger
ATT
ATT
ATT
ATT
Output pulse
Combined pulseOptional pulse
Principle of electrical pulse generation
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Yb:fiber laser system
Generation system of optional pulse shape
Generation system of optionalpulse shape
Output
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Electrical pulse Laser pulse
2ns/div. 2ns/div.
(a)
(b)
(c)
Generation of optional laser pulsecorresponding to electrical pulse shape
PC
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8 x 12 mm Rod, 2 pass
5 W
200 W
~5000 W
(Regen. Amp) Fiber Front-end
SBS PC Mirror
to Target Chamber/SBS Pulse Compression/Higher Harmonic Gen./Control of Focus Pattern
50 W
Regenerative amplifier replace to Yb fiberlaser for high average Nd:YAG laser.
Reg.Amp+ Pre AmpFiber Amp. Fiber Osc.
2 x 4 mm Rod, 2 pass
2 x 6 mm Rod, 2 pass
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Regenerative amplifier Yb:fiber(LMA) amplifierOutput 5W(1mJ, 5kHz) Now : Output 6.6W (66µJ, 100kHz)
In future: Output 30-50W (3-5mJ, 10kHz)Repetition rate 5kHz (PC limit)Pulse duration 3 ns (cavity length)Beam quality good(M2=1.5-2)Efficiency low
1-100kHz (Repetitious)Optional pulse shape and width (1-100ns)Excellent (M2=1.1)High
Comparison with regenerative amplifierand Yb LMA fiber laser
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LD978nm30 W
Optical stage
Output
Optical stage
Dichroic Beam-splitter Mirror(980nm T=95%,1064nm R=95%)
Isolator IsolatorYb fiber laser system
PM-Yb fiberLMA 30µm/400µm,L=4 mAbsorption 4dB/m @975nm
Input power4mW(4nJ, 1-50kHz)t=13, 30 ns
H.W. Plate
ILE Osaka University
Experimental layout of PM-Yb LMAfiber amplifier
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Output power depend on bending radius for PM-Yb LMA fiber amplifier
0
1
2
3
4
5
6
7
0 5 10 15 20 25 30 35
Ampl
ified
out
put p
ower
(W)
LD power (W)
Max.6.6W(@ 100kHz) Max.0.66mJ(@10kHz)
PM-Yb fiber LMA, 30µm/400µm, L=4m
Input 14mW
R=75mm(10-100kHz)
R=50mm(10kHz)
R=100mm(10-100kHz)
Bending radiusR
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ILE Osaka University
Propagation loss and output beam qualitydepend on bending radius
for PM-Yb LMA fiber amplifier
Bending radiusR
0.01
0.1
1
10
100
1000
0 20 40 60 80 100 120 140 160Bending radius [mm]
Prop
agat
ion
loss
[dB]
LP11
LP01
LMA, 30µm/400µm,NA 0.06
X -1.1 D.L. X 1.1 D.L. X 1.15 D.L.
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0
5
10
15
20
25
30
0 20 40 60 80 100
Out
put p
ower
(W)
LD input power (W)
Max.output 30W t=10 ns 300µJ / pulse 100kHz
X 1.1 D.L.
1054 nm1064 nm1080 nm
High power operation for PM-Yb LMA fiber amplifier
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LD978nm30 W
Optical stage
Optical stage
IsolatorYb fiber laser system
PM-Yb fiberLMA30µm/400µmL=4.3m
Input power4mW(4nJ, 1-50kHz)t=13ns
H.W. Plate
Isolator
LD978nm100 W
5W(0.5mJx10kHz)
50W(0.5mJx100kHz)
Experimental layout for PM-Yb LMA fiberamplifier(50 W, 0.5mJ, 100kHz)
(a) LMA-50/350L=3.4 m
(b) PCF-MMA50/390L=3 m
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600mm
1st fiber amp.
2nd fiber amp.
LD 30W
LD 100W
Photograph for PM-Yb LMA fiber amplifier(50 W, 5mJ, 10kHz)
50W Output
5W Output
600mm
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0
10
20
30
40
50
0 10 20 30 40 50 60 70 80
Out
put p
ower
(W)
LD pump power (W)
1
10
100
1000
10000
0 10 20 30 40 50 60 70 80
Gai
n
LD pump power (W)
Max. 40W, Efficiency 54% G=1500, g=0.022/cm
0. 035 W1.50 W3.70 W5.20 W
Input power
Core 50µmClad 350µmNA 0.06, 12dB/mL=3.4m
Near-fieldpattern
Laser output power and gain characteristics(1)
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Conclusion
Generation of optional pulse shape by Yb doped fiber laser system for EUV lithography laser The optional pulse shape generator by Yb doped fiber laser system. Yb fiber laser system operated the polarization-maintained pulsed for single
transverse and -longitudinal mode using fiber Bragg grating (FBG). The laser oscillator can be tuned at four wavelengths of 1030, 1053, 1064 and 1080 nm. This system generates optional pulse shapes that sliced up the Yb fiber oscillator by a
LN (LiNbO3) intense modulator with 12.5-GHz bandwidth. The several output waveforms were obtained including rectangular pulse from 1ns to
12.5 ns with a 500-ps rise time, and Gaussian pulse from 1 to 25 ns. The highest output energy of about 250 nJ for 10-ns Gaussian pulse was achieved at
100-kHz repetition rate. The output power has been increased over 30W (300µJ, 100kHz) by a 30-µm core Yb
double-clad polarization-maintained LMA fiber and 57W (570µJ, 100kHz) by a50-µm core MMF fiber