EXAレーザー応用科学

レーザー技術から見た視点

植田憲一 電通大レーザー新世代研究センター

大型レーザー応用科学意見交換会

KTP東京駅日本橋ビジネスセンター

2010年12月16日

コヒーレントビーム結合技術がキーとなる。

インコヒーレント伝送と集光点コヒーレント結合

レーザー技術の基礎としての光学薄膜損傷機構の物理

位相制御位相共役鏡技術

今日のレーザー技術が新しい科学を可能にする。

人類が手に入れたレーザー技術を組み合わせれば、ペアクリエーションに代表される高強度場物理が、夢ではなくなったというのが、研究推進の原動力となっている。

ELI proposal: Coherent combining of millions fiber lasers

Big challenge

Toward Ultra-high Intensity Lasers

Application of Ceramic Lasers

Introduction of scientific front

Ken-ichi Ueda

Institute for Laser Science

Univ. of Electro-Communications

Chofu, Tokyo, Japan ueda@ils.uec.ac.jp

LCS-6, Muenster, Germany, Dec. 8, 2010

コヒーレントビーム結合が鍵

Power scaling of solid state lasers

Dream of coherent combining

Mode coupling distance

Phase locked multi-beam solid state laser

Solid state laser embedded the gain volume in mode coupling distance.

Active photonic crystal is possible?

N =2,3,4,6

>100, >1000, >10000

Fiber bundle pumping

DKDP OPA

Signal 1 beam 100J/

0.5ns@1100nm

Output 1 beam

@1100nm 4 beam pumping

1ns@527nm

OPA

output

Pump

Focusing spot

Near field

phase profile

Random phase

pumping Wide band DKDP (13% D to H)

Beam combining in OPA (JAERI/ILE Osaka)

Beam Cleaning & Combining

in 1980’

J. Eggleston (LANL), IEEE QE-22, 1942, 1986.

Pulse Compression by Backward SRS

K. Ueda, H. Nishioka, K. Kimura, H. Takuma, Advanced Techniques of High Efficiency Pulse

Compression for KrF Lasers, Laser Particle Beams, vol.11, 31-42 (1993).

Raman compression system

in SPRITE, RAL

RAL, J. Modern Optics, vol.41, 1203, 1994.

High-average-power, high-brightness Nd:glass laser

technology (C.B. Dane, L.A. Hackel, LLNL)

UCRL-LR-105821-97-4, p.239

NIF-ARC laser: Multi beam coherent combining on focal spot. Advanced Radiographic Capability

High Power Coherent Beam Combining Tech will be

demonstrated in ARC (Advanced Radiographic Capabilit)

laser.

N: Number of beams N times focus energy

N2 times peak intensity

Mode-Locking Laser and Phase-Locked Arrays

Mode-locking in the same volume generates ultrashort pulses.

Phase-locked array locks modes separated in space and frequency.

1

2

3

4

5

=const

Ultrashort pulses

Pulse compression by coherent

combining of Fourier pulses on target

0

2

3 4

5 6

78

ELI proposal: Coherent combining of millions fiber lasers

Big challenge

m480

m9.7

m11

Ｙｂ添加マルチコアファイバー

067.0:NAコアの46.0:NAクラッドの

584.1 NAd

V

d

Talbot共振器ビームパターン

近視野像

遠視野像

閾値以下(ASE) 75mW 6.36W

Technique for translating light wave frequency by using an

optical ring circuit containing frequency shifter

Opt. Lett., vol. 17, 1307 - 1309, 1992.

K. Shimizu, T. Horiguchi, Y. Koyamada

Ｇ

AOM

+ 0+6

0+5 0+ 4

0+3 0+ 2

0+

-G

Problem: Max number of loop is limited by ASE amplification.

Basic concept of unlimited amplification: Zero gain amplification

Negative feedback for constant output

Spectrometer without dispersion elements

Ｇ

AOM

+ 0+6

0+5 0+ 4

0+3 0+ 2

0+

-G

0+6 0+5

0+ 4 0+3

0+ 2 0+

Broadband short pulse

Stabilized

pulse

Pulse compressor by AWG

+ fiber delay optics

MOPFA coherent array

•Complicated phase-locking servo system is required.

•Temperature drift & nonlinear phase fluctuation by huge B-integral

impose serious difficulty on scaling on power & array number

Straightforward, certain method..? N=2 10W S. Augst, T. Y. Fan et al., Opt. Lett. 29, 474 (2004).

N=4 2W J. Anderegg, M. Wickham et al., Photonics West 2003, 4974-03.

by courtesy of Dr. M. Wickham (Northrop Grumman)

High-power operation degrades phasing

H. Bruesselbach, M. Minden et al., CLEO 2005, CMDD4

HRL Lab.

“Longitudinal modes “collapse” and then constructive interference

supermodes cannot be maintained….”

“Self-organization by

nonlinear phasing”

9 of 19 can be phased.

Fiber laser coherent array by self-Fourier method By courtesy of Dr. C. J. Corcoran (Corcoran Engineering)

Appl. Phys. Lett. 86, 201118 (2005).

Linear Array with 7 Fiber Laser Elements

FL

Output

Fiber

Lasers

End

Mirror

Fourier

Lens

Microlens

Array

Cylindrical

Lens

Incoherent operation

(Mirror misaligned)

Coherent operation

(Mirror aligned)

Far-

Field

Far-

Field

Near-

Field

Near-

Field

predicted far field

F (F(x)) = F(x)

1W@1.07m7

Degree of

coherence = 0.73

WC1 2-Dimensional Waveguide Coherent Beam Combiner Scott Christensen and Olivia Koski

Lockheed Martin Coherent Technologies

Abstract: We report on a novel coherent beam combiner with the potential to completely eliminate

side-lobe power in the combined beam, without the use of vulnerable refractive or diffractive optical

elements in the beam train, allowing scaling to high power. We have completed a low power, 2-

dimensional proof-of-concept demonstration. The 2-D beam combiner can be used with various

lasers but is particularly well suited for combining the outputs of fiber lasers.

Ls=4nh2/

レーザー研究に関する共通問題 ELI, Gekko EXA 超高出力レーザーシステム 産業用高出力レーザー 重力波アンテナ PPM Loss Mirror 高エネルギー物理 コンプトン散乱 γ線発生 光子蓄積型光共振器 多モード光コム蓄積 ミラー損傷の研究は１９８０年代から進んでいない。 ミラー損傷のダイナミック観測研究 誘電体、固体表面内の光誘起電流の計測 Thin Disk Laser 接合技術の物理が必要 計測法の開発 マルチコアファイバーのコヒーレント位相同期技術

誘電体多層膜のレーザー損傷メカニズムの研究

植田憲一

電通大レーザー研

植田憲一、萩原真一、北谷文人、宅間宏： 光音響効果による初期的レーザー損傷の検出； レーザー研究、vol.15, 22-31 (1987).

微小吸収を測定して、高耐力光学膜を開発する。

エキシマレーザー用高耐力ミラーの開発経験

フッ化膜が強い！

電子を捕まえる。

ネット利得ゼロの条件で損傷する。

初期電子の生成

電子雪崩と再結合

• Feed back mirror > Counter propagating beams > Standing wave > Density

modulation

• Standing density modulation locks the ignition position of the moving Bragg

grating.

• The Bragg grating locks the phase of the SBS wave.

• Phase controlling of SBS wave is possible by positioning the feed back mirror.

Concave MirrorLens

SBS Cell#1

SBS Cell #2

Concave Mirror

SBS Cell #1

SBS Cell #2

(a)Concentric type (b) Confocal type

“Self-phase control” method

Intensity profile of interference for 160 shots

Lens(f=250mm)

SBS Cell #1(l=500mm)

SBS Cell #2

Intensity profile of interference 0 50 100 150-180

-90

0

90

180

Ph

ase

diff

ere

nce

(d

eg

ree

)

Count of shots

Phase of the conventional SBS-PCM

H. J. Kong, S. K. Lee, and Y. S. Kim, “Phase locking of two beams using stimulated Brillouin phase conjugate

mirrors, LO2003, XIth Conference on Laser Optics, St. Petersburg, Russia (June 30 – July 04, 2003).

0 50 100 150 200-180

-90

0

90

180

Ph

ase

diffe

ren

ce

(d

eg

ree

)

Count of shots

Intensity profile of interference for 239 shots

Average fluctuation ~ λ/7.4

Confocal type

Phase controlled result – Wave-front division

H. J. Kong, S. K. Lee, and Y. S. Kim, “Phase locking of two beams using stimulated Brillouin phase conjugate

mirrors, LO2003, XIth Conference on Laser Optics, St. Petersburg, Russia (June 30 – July 04, 2003).

0 50 100 150 200-180

-90

0

90

180

(

deg

ree)

Count of shot

Ep=10 mJ

Intensity profile of interference for 220 shots

Average fluctuation ~ λ/35.7

Phase controlled result – Amplitude division

S. K. Lee, H. J. Kong, and M. Nakatsuka, Applied Physics Letters 87, 161109 (2005).

Experimental setup for the wave-front

dividing 4-beam combination

PB1&PBS2, polarizing beam splitters; HWP1&HWP2, half wave plate; P1, P2&P3, 45 degree prisms; BS, beam splitter; W,

wedged window; FR1, FR2, FR3&FR4, Faraday rotators; C1, C2, C3&C4, concave mirrors; PZT1, PZT2&PZT3,

piezoelectric translators.

FR1

Amplified

output

Input

beam SBS cell 1

SBS cell 2

Reference

beam

Nd:YAG laser

oscillatorHWP2

PBS1

PBS2

BSCCD

camera

P1

P2

P3

W

M1

M2

M3

AMP1

FR2AMP2

FR3AMP3

FR4AMP4

SBS cell 3

SBS cell 4

C1

C2

C3

C4

Phase control electronics

HWP1

6 mm

1.5 mm

4-beam aperture

f = -50 mm

f = 200 mm

f = -50 mm

f = 200 mm

Feedback

signal

PZT1

PZT2

PZT3

J. S. Shin, S. Park, H. J. Kong, and J. W. Yoon, Applied Physics Letters. 96.131116, 2010.