Self-reflection and high-order harmonic generation due to plasma effect on the surface of a solid insulator: Normal incidence

Abstract

We consider the transmission of an intense short light pulse through a solid insulator undergoing tunnel ionization sufficiently high to change the sign of the plasma dielectric function from positive to negative. This may cause a strong reflection of the incident wave from the insulator surface. The ionization process also involves harmonic generation due to a sharp change in ionized electron density. We describe a theoretical scheme based on the Floquet expansion that provides a qualitative analysis of both self-reflection and the harmonic spectrum. Comparison of the exact numerical solution with the slow envelope of the fundamental harmonic shows that the Floquet expansion approach fails at the limit of strong reflection. We calculate the harmonic spectrum using the exact wave equation and study its peculiar features when reflection increases.