Femtosecond laser irradiation induced-high electronic excitation in band gap materials: A quantum-kinetic model based on Boltzmann equation

A quantum kinetic approach based on the Boltzmann equation is employed to describe the response of dielectric and semiconductor materials to high electronic excitation induced by laser irradiation. The formalism describes from the initial photo-ionization inter-band processes through free carrier absorption inducing additional impact ionization to the final heat up by electron–phonon coupling. Swift thermalization through electron–electron scattering, Auger recombination and formation of free excitons, their self-trapping and subsequent non-radiative decay are included. The energy exchange between the electrons and phonons are given by a separate equation for the lattice temperature where the rates of energy transfer from the electrons to the lattice per unit volume are defined quantum mechanically. As a result of our calculations the electron energy distribution function, average kinetic energy of the electron system and electron density are obtained as a function of laser intensity, laser photon energy (wavelength) and laser pulse duration. Examples of application in fs-laser irradiated-silica are discussed.