Off-axis XUV harmonics from relativistic laser - gas jet interaction

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*; 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 present the discovery of strong off-axis XUV high-order harmonics generated in the interaction of relativistic-irradiance ( 10 W/cm) multi-terawatt femtosecond laser pulses with gas jet targets. The results are obtained using the J-KAREN laser facility in Kansai Photon Science Institute, JAEA in the relativistic regime of high-order harmonics generation in gas targets discovered by us. We have performed 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. Our results are important for many research fields and technological areas requiring a bright coherent X ray or XUV source for pumping, probing, seeding, imaging, or attosecond science.