1. Solid laser system 2015.02.19 Mitsuhiro Yoshida

2. Properties of laser medium LD Pump (808nm) Nd:YVO4 Nd:YAG SHG(532nm) 40% FHG(266nm) 20% 5HG(213nm) 3% τ ～ 200μs, 40% Nd-doped Yb-doped Ti-doped LD Pump (941/976nm) Yb-glass Yb:YAG Yb:BOYS 1064nm 808nm 941/976nm 1040nm τ ～ 900μs, 40% Pump (808nm) Nd:YAGSHG 40% 1064nm 808nm Ti:Sapphire 532nm 800nm τ ～ 3μs, 40% τ=200μs, 40% ○ 4-state laser is easy to operate. ○ High power pump LD is available. ○ Large crystal is available × Pulse width is determined by SESAM. (Gaussian) ○ Wide bandwidth => pulse shaping ○ Long fluorescent time => High power ○ Fiber laser oscillator => Stable ○ Small state difference × ASE × Absorption ○ Very wide bandwidth ○ High breakdown threshold × Low cross section × Short fluorescent time => Q-switched laser is required for pumping Pump TW laser is based on Ti-Sapphire SHG(520nm) 40% FHG(260nm) 20% 5HG(208nm) 3% SHG(400nm) 40% THG(266nm) 20% FHG(200nm) 10% Best for RF-Gun Nd laser system for 3-2 RF-Gun Ti:Sapphire laser system for beam monitor.

3. Yb-Fiber Frontend Superconitnuum broadning OPCPA Yb:YAG Thin Disk Laser schemes Ti-Sapphire Oscillator Ti-Sapphire Oscillator Many commertial product. - How to maintain continuously? - How to generate 2-bunch ? Amplifier Nd:YAG CPA Yb:BOYS, Yb:CaF2 - Broadband 1030nm Pump 940nm LD Flash pumped η ～ 0.5% η ～ 40% LD pumped - Very high gain - Critical incident angle - Fiber laser is stable in principle. - High efficiency (long fluorecense lifetime) - Low gain at room temperature => Lower temperature

4. Nd based solid laser (3-2 DAW RF-Gun)

5. Nd based laser system Nd:YVO 4 oscillator + Nd:YAG multi-pass amplifier 30 ps (10 mm)

6. Nd based laser system (renewed)

7. 発振器

8. 増幅部

10. 波長変換部

11. Yb solid laser (A-1 RF-Gun)

12. Characteristics of Yb doped laser Long fluorescent lifetime ～ 1ms Wideband High quantum efficiency X Quasi-three level => Absorption at room temperature X Small cross section Yb Base material Stimulated emission cross section [10-20cm2] Fluoresce nce lifetime [ms] Thermal conductivity [W/mK] Fluorescence spectral width [nm] Fourier minium [fs] Experimental records Pulse width [fs] Average power [W] YAG20.95 11 9120 3400.11 1360.003 73016 81060 KYW30.73.32450710.12 KGW30.73.32547 1120.2 1761.1 glass0.632-3533360.065 GdCOB0.352.72.14427890.04 BOYS0.22.51.86019 690.08 860.3 YVO4-1.2---610.054 CaCdAlO40.55-6.9--470.038

13. Temperature dependence of Yb:YAG Improvement of thermal and emission property (Thermal lens effect) (Excitation density) 300K 30kW/cm 2 Pertier GM+He 300K P/P 0 = exp(g 0 z) ～ 2 150K → g = 7 [cm -1 ] 10 W/m/K, dn/dT = 8ppm/K @ 300K 25 W/m/K, dn/dT = 3ppm/K @ 150K ↑150K 1/6 Thermal lens Same gain @ 1/3 excitation density → ↓ 150K => 1/20 thermal lens

14. Yb:YAG thin disk Laser at room temperature 30% efficiency was achieved at room temperature Yb:YAG Yb disk laser 940nm LD (2.4 kW / module) Yb:YAG disk 10 % doped 2mm thickness

15. Yb:YAG 10% dope, α=12/cm, 5kW/cm 2, 25Hz 0.5t 1t

16. How to generate 2-bunch Amplification time of standard regenerative amplifier (usually adopted in commertial product) is around 1  s. Two regenerative amplifier (not good) Large regenerative amplifier (built & failed) – Unstable output energy due to low gain. – Difficult to compensate thermal lens. High gain fast regenerative amplifier (built & failed) – Difficult to reduce the ghost pulse from first bunch due to limted extinction ratio of pockels cell. Multi-pass amplifier (current configuration) – More gain is required for the balanced 2-bunch. OPCPA (future candidate)

17. Large regenerative amplifier for 2-bunch operation 100ns (2-bunch)+20ns (Pockels cell speed) = 36m => round trip + polarization => resonator length > 9m : 2.25m×3 + 0.75m×4 R=3m (f=1.5m) R=3m R=1.5m 2.25m λ/4 f=300mmf=100mmf=75mmf=200mm    Input λ/4 Output

18. A1 ハット内概要図 出入口 ファイバー アンプ ファイバー プリアンプ ストレッチャー パルスピック 2 段目 マルチパス アンプ 3 段目 マルチパス アンプ 4,5 段目 マルチパス アンプ GR_A1 へ シャッ ター 発振器オシロ Ch1( 黄 ) に該当する。 増幅器オシロ Ch2( 緑 ) に該当する。 増幅器オシロ Ch3( 橙 ) に該当する。 制御 ラック ファイバー アンプ 波長変換 1033nm ↓ 532nm 発振器 A 発振器 B マルチパスアンプ 1 段目

19. 1pass LD Laser Diode 2pass 3pass 4pass 5pass Original multi-pass amplifier (5-pass) Balanced offset lens to avoid damage. To obtain higher gain, => Higher pumping density  Thermal lens  Focused type amplifier to avoid thermal lens.

20. New high gain multi-pass amplifier (10-15 pass x 2 loop) to simplify the laser LD Laser Diode INPUT OUTPUT 1pass 10-15pass ←

21. Final amplifier LD Laser Diode 1pass 2pass 3pass 4pass 5pass Uniform pumping is required. Low gain G=1.3 => Multi-pass

22. Main Yb:YAG Amplifier UV conversion (BBO SHG+FHG) => 1 mJ maximum @ 258 nm Laser instability is caused by: -ASE of fiber amplifier. -Pointing fluctuation from fiber amplifier. -Stability of pump laser (Upgrade of charger is required) -Separated optical table between fiber and solid laser. Current situation: -Instability => -No spatial shaping -No compressor Typical charge distribution Focused type multi-pass amplifier < 1mJ Non-Focused type amplifier > 10 mJ - High gain - Focused at crystal leads to avoid thermal lens effect. -Low gain -Uniform pumping is required.

23. :Mirror :Lens From multi-pass amplifier 1033nm532nm BBO :Wave Plate ： Telescope Wavelength conversion Power monitor Piezo mirror Laser diagnostics (Streak camera / Beam profile)

24. Inside Gun laser case

25. :Mirror :Wave Plate トンネル内 GR_A1 BOX 内部 レーザーハットよ り 532nm BBO 結晶 リモートで角度を調 整 266nm Cylindrical Lens ミラー リモートで X 軸、 Y 軸を調整 テレスコープ リモートでレンズ位置を調整 安全系シャッター GR_A1 レーザープロファイルモニター 波長板で反射した光をモニターしている。

26. UV conversion efficiency improvement Nd:YAG 1ω Nd:YAG 2ω Nd:YAG 4ω Nd:YAG 5ω Crystal BBOCLBO 10 Hz250 mJ90.3 mJ50.2 mJ36.0 mJ conversion efficiency (%) 36.1220.0814.4 100 Hz250 mJ90.3 mJ44.9 mJ19.8 mJ conversion efficiency (%) 36.1217.967.92 Reference [1] Nd:YAG Laser [1] Pulse width : 3.5 ns Max Energy : 400 mJ/pulse single longitudinal mode single transverse mode (top-hat) 70.71 % 44.10 % [1] K.Deki, et al., “CsLiB 6 O 10 (CLBO) を用いた 193nm 光源の開発 ”, 光技術情報誌「ライトエッジ」 No.18 [2] Yap YK, et al., "High-power fourth- and fifth-harmonic generation of a Nd:YAG laser by means of a CsLiB(6)O(10).", Opt Lett. 1996 Sep 1;21(17):1348-50. Reference [2] QE = 9.10×10 -4 @213nm QE = 1.54×10 -4 @266nm ×6 【 QE of Ir 5 Ce photocathode 】 Photocathode: Ir 5 Ce compound Laser : 5 th harmonics (CLBO) 【 Conversion efficiency of fundamental wave 】 【 The optimal combination 】

27. Temperature dependence of Yb:YAG Improvement of thermal and emission property (Thermal lens effect) (Excitation density) 300K 30kW/cm 2 Pertier GM+He 300K P/P 0 = exp(g 0 z) ～ 2 150K → g = 7 [cm -1 ] 10 W/m/K, dn/dT = 8ppm/K @ 300K 25 W/m/K, dn/dT = 3ppm/K @ 150K ↑150K 1/6 Thermal lens Same gain @ 1/3 excitation density → ↓ 150K => 1/20 thermal lens

28. Issues on Yb based laser system Yb-fiber oscillator – 1030nm oscillator is not stable. – Broadband oscillator is very stable => ASE reduction is required. Yb-fiber amplifier – Lack of pulse energy – Lifetime and stability of PCF fiber. Yb-disk amplifier: (Regenerative amplifiers were failed) => Multi-pass amplifier for 2-bunch operation. => More gain is required for balanced 2-bunch energy. – 5 Hz => Soldered cryatal => 25 Hz operation => x 2 system => 50Hz before May 2015 – Reduce thermal lens effect and simplify laser system => Focused type multipass amplifier x2 + Non-focused multipass amplifier => Cryogenic Yb laser at next summer Temporal shaping – Compressor and Slit Stability improvement – Casing of each block. – Gas filled or vacuum laser transportation to improve pointing stability. – Assemble on one large optical table (new laser room). – Feedback (pointing / amplitude). – Increase monitor points (pointing / power / beam pattern).