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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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ILE Osaka University

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

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Experimental layout of PM-Yb LMAfiber amplifier

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ILE Osaka University

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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ILE Osaka University

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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ILE Osaka UniversityILE Osaka University

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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ILE Osaka University

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