1. Isao MATSUSHIMA, Hidehiko YASHIRO, Toshihisa TOMIE National Institute of Advanced Industrial Science and Technology (AIST) C2 1-1-1, Umezono, Tsukuba, 3058568, Japan *This study was partly financially supported by the Budget for Nuclear Research of the Ministry of Education, Culture, Sports, Science and Technology, based on screening and counseling by the Atomic Energy Commission. Laser system for laser-plasma X-ray source 10 kHz 54 W Ti:sapphire regenerative amplifier as a pumping laser of a laser-plasma X-ray source

2. Laser-Plasma X-ray Source X-ray, λ~nm, <ns blight point source Target Plasma High Temperature <100μm ϕ, Ionization >ps, Laser >>mJ, ~10μm ϕ ps<τ<ns >10 11 W/cm 2 * EUPS; extreme ultraviolet (EUV) excited photoelectron spectroscopy *EUV source for defect inspection of multi-layered mask blanks *EUV lithography *X-ray microscopy of living cells multi kHz repetition-rate is required for high throughput

3. Laser-Plasma EVU Source EUPS4 EUPS; extreme ultraviolet (EUV) excited photoelectron spectroscopy Our Application of Laser-Plasma Novel surface analysis Energy resolution: better than 0.3 eV Spatial resolution: better than 1 μm

4. MOPA Ti:S commercial Ti:S Fiber Laser Our Target Area We need Multi-kHz Multi-mJ sub-ps Laser 1.I. Matsushima, H. Yashiro, T. Tomie, “A 37% Efficiency, Kilohertz Repetition Rate Cryogenically Cooled Ti:Sapphire Regenerative Amplifier,” Jpn. J. Appl. Phys. 44, L823-L826 (2005). 2. I. Matsushima, H. Yashiro, and T. Tomie, "10 kHz 40 W Ti:sapphire regenerative ring amplifier," Opt. Lett. 31, 2066-2068 (2006). 1 2

5. Key Technologies Thermal lensing effect Symmetric ring resonator Low loss and high gain High-quality pump beam High-average power Ti:Sapphire regenerative amplifier Cryogenic cooling Good beam quality High efficiency Mode-volume matching

6. Fig. 1. Schematic drawing of a ring regenerative amplifier. A cryogenic-cooled Ti:sapphire rod is kept in a vacuum cell and placed at the beam waist for f = 1 m intra- cavity lens. M1~ M6 are cavity mirrors;  /2 is a half-wave plate; PC is a Pockels cell; TFP is a thin film polarizer; FI is a Faraday isolators; and AO2/G is a pump laser. High-average power Ti:Sapphire regenerative amplifier

8. Pump Laser AO2/G (PowerLase) ×2 High repetition rate : 10 kHz High pulse energy : 8mJ x 2 Good beam quality : M 2 =23.5 for high gain

9. Cryogenic Cooling reduce thermal lens

10. 10 kHz Ti:Sapphire regenerative amplifier Fig. 3. Output power of the regenerative amplifier at 10 kHz as a function of pump power.

11. Output beam quality of 10 kHz regen amp 500μm Focusability: 2XDL ⊃ >80%Energy Far field image (56W before compression) Compressability: 82 fs

12. Discussion Scale up to kW? High power pumping green laser Cryogenic cooling for kW un-known non-linear losses at high pumping power decrease in conversion efficiency

13. Summary 10kHz 180W Pump before cpmpression 54W outout 2XDL ⊃ >80%Energy Compressability: 82fs High average power and pulse energy Acknowledgments The liquid nitrogen cryogenic cooling system was designed with advices from AIST Cryogenic Technical Center. 5.4 mJ/pulse conversion efficiency 30% The highest output power in the world from a single stage single rod kHz Ti:Sap regen Scalability to higher output power was discussed.

15. Requirements of lasers for x-ray generation Pulse Energy: Multi-mJ Repetition rate: Multi-kHz Focusability: a few μm Minimum pulse duration: 100fs High-efficiency Small and simple