PUB - Publikationen an der Universität Bielefeld

In this paper we present a Floquet-Bloch analysis of photoemission of electrons and high harmonic generation from a crystal surface subjected to intense laser fields. We also investigate harmonic generation from single and double quantum-well structures by direct numerical solution of the associated time-dependent Schrodinger equation. The results of simulations of the photoelectron emission spectra show a whole set of new phenomena including above-threshold surface-emission bands of photoelectrons separated exactly by the photon energy, and modulation of the envelope of the spectrum. Simulation of the emission spectrum of high harmonics from an electron beam reflected from the surface in the presence of a laser beam at grazing incidence show a sequence of emission "hills" associated with strong enhancements of the high-harmonic signals. The results of photoemission and high harmonic generation spectra are interpreted in terms of modification of the band-structure of the crystal by the laser field. Finally, efficient harmonic generation from quantum-well structures are shown to be possible; it is suggested that this can provide a source of generating coherent radiation in far-infrared, at as yet unavailable wavelengths.