Frequency multiplication of light back-reflected from a relativistic wake wave

相対論的航跡波によって反射された光の周波数上昇

Pirozhkov, A. S.; Ma, J.-L.; 神門 正城; Esirkepov, T. Z.; 福田 祐仁; Chen, L. M.; 大東 出; 小倉 浩一; 本間 隆之; 林 由紀雄; 小瀧 秀行; 匂坂 明人; 森 道昭; Koga, J. K.; 河内 哲哉; 大道 博行; Bulanov, S. V.; 木村 豊秋; 加藤 義章 ; 田島 俊樹

Pirozhkov, A. S.; Ma, J.-L.; Kando, Masaki; Esirkepov, T. Z.; Fukuda, Yuji; Chen, L. M.; Daito, Izuru; Ogura, Koichi; Homma, Takayuki; Hayashi, Yukio; Kotaki, Hideyuki; Sagisaka, Akito; Mori, Michiaki; Koga, J. K.; Kawachi, Tetsuya; Daido, Hiroyuki; Bulanov, S. V.; Kimura, Toyoaki; Kato, Yoshiaki; Tajima, Toshiki

A method of coherent high-frequency electromagnetic radiation generation, proposed in [S. V. Bulanov, T. Zh. Esirkepov, T. Tajima, PRL 91, 085001 (2003)], is experimentally demonstrated. This method is based on the radiation frequency multiplication during reflection at a mirror flying with relativistic velocity. The relativistic mirror is formed by the electron density modulations in a strongly nonlinear wake wave, excited in an underdense plasma in the wake behind an ultra-short laser pulse. In our experiments, the reflection of a counter-crossing laser pulse from the wake wave is observed. The detected frequency multiplication factor is in the range from 55 to 114, corresponding to a reflected radiation wavelength from 7 to 15 nm. This may open a way towards tunable high-intensity sources of ultra-short coherent electromagnetic pulses in the extreme ultraviolet and X-ray spectral regions. Parameters of the reflecting wake wave can be determined using the reflected radiation as a probe.