Demonstration of laser-frequency upshift by electron-density modulations in a plasma wakefield

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

In a plasma wake wave generated by a high power laser, modulations of the electron density take the shape of paraboloidal dense shells, moving almost at the speed of light. A counter-propagating laser pulse is partially reflected from the shells, acting as relativistic flying mirrors, producing a time-compressed frequency-multiplied pulse due to the double Doppler effect. The counter-propagating laser pulse reflection from the plasma wake wave accompanied by its frequency multiplication (with a factor from 50 to 100) was detected in our experiment.