Novel X-ray generation schemes based on electron cusps formed via intense laser plasma interaction

Kando, Masaki; Pirozhkov, A. S.; Esirkepov, T. Z.; Kawase, Keigo*; Ragozin, E. N.*; Faenov, A. Ya.*; Pikuz, T.*; Fukuda, Yuji; Sagisaka, Akito; Mori, Michiaki; Koga, J. K.; Kawachi, Tetsuya; Ogura, Koichi; Daito, Izuru; Chen, L. M.*; Hayashi, Yukio; Kotaki, Hideyuki; Kiriyama, Hiromitsu; Okada, Hajime; Kameshima, Takashi*; Nishimori, Nobuyuki; Kondo, Kiminori; Tajima, Toshiki; Daido, Hiroyuki; Kato, Yoshiaki ; Bulanov, S. V.

We present the results of two kinds of experiments and theoretical description for generating coherent, ultrashort, tunable X-ray photons. Nonlinear interaction of intense laser pulses with plasma creates stable, specific structures such as electron cusps. For example, wake waves excited in an unerdense plasma by intense, short-pulse laser becomes dense and propagate along the laser pulse. These wake waves act as relativistic flying mirrors. The flying mirror can reflect a counter-propagating laser pulse and directly convert it into high-frequency radiation, with a frequency multiplication factor 4 and a pulse shortening with the same factor. We present the results of experiments. Another mechanism of coherent X-ray generation is based on a single laser pulse irradiating gas jet target. In this case, bright high-order harmonics of both odd and even orders are emitted in the forward direction. We attribute this to the synchrotron or nonlinear Thomson scattering of a bunch of electrons in the cusp interacting with the laser.