On-axis and off-axis high order harmonics generation by relativistic laser in gas jet target

ガスジェットターゲットにおける相対論的レーザーパルスによる同軸,非同軸方向への高次高調波発生

Pirozhkov, A. S.; 神門 正城; Esirkepov, T. Z.; Pikuz, T.; Faenov, A. Ya.*; 小倉 浩一; 林 由紀雄; 小瀧 秀行; Ragozin, E. N.*; Neely, D.*; 桐山 博光; 下村 拓也; 田上 学; 中井 善基*; 岡本 征洋*; 近藤 修司; 金沢 修平; Koga, J. K.; 福田 祐仁; 錦野 将元; 今園 孝志; 長谷川 登; 河内 哲哉; 大道 博行; 加藤 義章* ; Bolton, P.; Bulanov, S. V.; 近藤 公伯

Pirozhkov, A. S.; Kando, Masaki; Esirkepov, T. Z.; Pikuz, T.; Faenov, A. Ya.*; Ogura, Koichi; Hayashi, Yukio; Kotaki, Hideyuki; Ragozin, E. N.*; Neely, D.*; Kiriyama, Hiromitsu; Shimomura, Takuya; Tanoue, Manabu; Nakai, Yoshiki*; Okamoto, Masahiro*; Kondo, Shuji; Kanazawa, Shuhei; Koga, J. K.; Fukuda, Yuji; Nishikino, Masaharu; Imazono, Takashi; Hasegawa, Noboru; Kawachi, Tetsuya; Daido, Hiroyuki; Kato, Yoshiaki*; Bolton, P.; Bulanov, S. V.; Kondo, Kiminori

We have recently discovered a new regime of high-order harmonic generation by multi-TW femtosecond lasers focused to gas jet targets, where comb-like spectra with hundreds of harmonic orders, reaching the photon energy of 500 eV, including the "water window" spectral range, were generated by either linearly or circularly polarized pulses. In this presentation we describe the results of new experiments with the J-KAREN laser in KPSI, JAEA, namely (1) the discovery of a strong off-axis XUV high-order harmonics emission, (2) the detailed study of the high-resolution on-axis harmonics spectra, and (3) the measurements of the harmonics source size and angular divergence which allow more accurate estimate of the peak spectral brightness, much more favorable compared to the previous conservative estimates.