Laser Plasma Soft X-ray Source in the Water Window Based on Cryogenic Targets

Abstract

To generate continuously repetitive soft X-ray pulses in the water window from laser-produced plasmas, a one-dimensionally translating substrate system with a closed He gas cryostat that can continuously supply various cryogenic targets has been developed. The system was successfully operated at a lowest temperature of 15 K and at a maximum up-down speed of 12 mm/sec. Solid Ar and N₂ layers were formed, and the water window spectra from them were studied. The emission intensity from Ar was found to be about 8 times stronger than that from N₂. Developed laser plasma source demonstrated high average power of 140 mW in the water window soft X-ray, when a commercial Nd:YAG Q-switched laser was used to irradiate a solid Ar target with energy of 1 J at a repetition rate of 1 Hz. It can be used for various applications, including soft X-ray microscopy, in place of synchrotron facilities.