Macroscopic Aspects of Resonant Generation of High-Order Harmonics in Indium Laser Plasma

Abstract

The generation of high-order harmonics at interaction of intense laser radiation with the plasma of the laser plume formed on an indium target surface has been investigated theoretically. The study is based on integrating the propagation equations for the fields propagating in plasma. The nonlinear polarization is calculated by solving numerically the Schrödinger equation for an ion in a strong laser field. The generating radiation frequencies corresponding to the multiphoton resonance with the indium ion transition from the ground state to the autoionizing state are considered. The macroscopic response at the resonant harmonic frequency is calculated as a function of the propagation length. It is shown that, in the case of generation in plasma consisting of singly ionized indium, the resonant contribution of ions to the phase mismatch can compensate for the contribution of free electrons. This occurs when the harmonic frequency slightly exceeds the resonant frequency. This compensation ensures relatively high generation efficiency.