Generation of hard X rays by femtosecond laser pulse interaction with solid targets in atmosphere

Zhidkov, A. G.*; Pikuz, S. A.*; Faenov, A. Y.; Chefonov, O. V.*; Ovchinikov, A. V.*; Agranat, M. B.*; Zigler, A.*

X ray radiation as high as 50 KeV, including K-shell spectra of Ba, have been observed during the interaction of low energy 0.65 mJ, 1 kHz femtosecond laser pulses focused on the solid target in air of atmospheric pressure. Possible mechanism of such generation by energetic electrons produced when the field strength in laser pulse wake exceeds the runaway threshold in air is considered. Multidimensional particle-in-cell simulations including optical field ionization of air confirm this mechanism.