Electron heating in the conduction band of insulators irradiated by ultrashort laser pulses

Abstract

We investigate the theoretical problem of electron heating in the conduction band of wide band gap insulators and semiconductors induced by intense femto-second Ti:Sapphire laser pulses. We analyze in detail the heating mechanism due to the sequence of direct interbranch transitions in the conduction band, which has been shown to be of crucial importance in previous work. This analysis is fulfilled by resolving the time dependant Schr\odinger equation (TDSE) in a basis of Bloch functions for the CsI crystal. The field is represented semiclassically and the laser-electron interaction is treated in the dipole approximation. The presented approaches are based on a one-active electron approximation. First the TDSE is solved in a basis of Bloch functions, in one dimension, the influence of laser and crystal parameters on the electron spectra is studied. The electron transfer from the lower conduction band to the higher one is already effective at intensity of $3\ifmmode\times\else\texttimes\fi{}{10}^{12}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$. Then the problem is solved in three dimension. The electron spectra is consistent with the experimental results, we note in particular the presence of a large plateau at intensities of the order of the terawatt per square centimeter.