Electron dynamics in transparent materials under high-intensity laser irradiation

Abstract

The energy of a laser beam irradiating a surface is primarily absorbed by electrons within the solid. In actual transparent materials, absorption is low. High-intensity lasers may, however, be absorbed by initi- ally bounded electrons through nonlinear processes. The increase of free- electron density leads eventually to dielectric breakdown, and the material becomeshighlyabsorbing.Wepresenttheoreticalstudiesonthedynamics of electrons in dielectrics under irradiation with a visible high-intensity laser pulse. We consider microscopic processes determining absorption, redis- tributionoftheenergyamongelectrons,andtransferofenergytothecrystal lattice. We review different aspects of electronic excitation, studied with time-resolved models as the Boltzmann kinetic approach and the time andspatialresolvedmultiplerateequation.Furthermore,weinvestigatecri- teria for damage thresholds. Two concepts are compared, namely a critical free-electrondensityandthemeltingthresholdofthelattice.Weshowthatin dielectrics both criteria are fulfilled simultaneously. Optical parameters depend on the density of free electrons in the conduction band of the solid, so the free-electron density directly leads to an increased energy absorption causing material modification. We present results on the spatial dependenceofdielectricbreakdown.©2012SocietyofPhoto-OpticalInstrumentation