Nonlinear inverse bremsstrahlung absorption in a photoionized plasma

Abstract

Nonlinear inverse bremsstrahlung absorption is investigated for a plasma photoionized in the Bethe regime of suppression of the ionization barrier, in which case the electron velocity distribution coincides with the distribution of atomic electrons. A comparison is made between the characteristic features of absorption in the cases where atomic electrons before ionization are in the ns and np states. It is established that, in the case of np states, the effective high-frequency conductivity is always nonlinear; in particular, for weak pump fields, it is proportional to the square of the pump field strength. The maximum plasma conductivity associated with p electrons is one order of magnitude lower than the maximum effective conductivity associated with s electrons, which creates conditions for less efficient plasma heating through inverse bremsstrahlung absorption.