Frequency filter of seed X-ray by use of X-ray laser medium; Toward the generation of the temporally coherent X-ray laser

Hasegawa, Noboru; Kawachi, Tetsuya; Kishimoto, Maki; Sukegawa, Kota*; Tanaka, Momoko; Tai, R. Z.*; Ochi, Yoshihiro; Nishikino, Masaharu; Nagashima, Keisuke; Kato, Yoshiaki* 

We evaluate the characteristics of a higher-order harmonics light as a seed X-ray amplified through the laser-produced X-ray amplifier. Narrow spectral bandwidth of the X-ray amplifier works as the frequency filter of the seed X-ray, resulting in that only the temporally coherent X-ray is amplified. Experimental investigation using the 29th-order harmonic light of the Ti:sapphire laser at a wavelength of 26.9 nm together with the neon-like manganese X-ray laser medium shows obvious spectral narrowing of the seed X-ray and amplification without serious diffraction effects on the propagation of the amplified X-ray beam. This implies that the present combination is potential to realize temporally coherent X-ray lasers, with the expected duration of several 100 fs.