Hard X-ray Emission from Femtosecond Laser Interaction in Overdense Plasmas

Abstract

The recent development of ultra-short pulse lasers has made possible the investigation of laser matter interaction at ultra-high intensities. For sub-picosecond pulses, a hot and overdense plasma is produced very rapidly during the rise of the pulse and further laser interaction occurs with this plasma. One of the results of the interaction is the generation of fast electrons and of intense hard x-ray emission. The x-ray pulse duration is determined by the mean free path of the fast electrons in the target material. It can be very short (< 1 ps) and its intensity sufficient to be registered by the usual methods. With high laser pulse repetition rates, it has been demonstrated [1] that one can obtain an instantaneous signature of fast-x-ray dense-matter interaction processes. The high energy of the x-ray photons (up to ≈ 1MeV) makes it possible to study small size objects and even to excite nuclear levels. Numerous papers [2-7] have been devoted to the study of femtosecond laser pulse interaction with plasmas. In this paper, we calculate the electron energy distribution function in the presence of the laser field, the absorption coefficient, and the parameters of the fast electron flux in the plasma. Our absorption results are in agreement with previously published [3-5] papers. A new feature of our calculations is the determination of the energy and spectrum characteristics of the hard x-ray pulse produced by the interaction of an intense laser with a solid-state target.