Modeling of laser-induced avalanche in dielectrics

Abstract

A study of the dependence of the laser-induced avalanche behavior on the intensity of irradiation in dielectrics is carried out. The avalanche rate is computed directly from the reduced equations, instead of the time dependent kinetic equations, thereby requiring less computational effort. For comparison, the calculations were carried out for both the flux-doubling model and the linear Fokker–Planck type equation for fused silica material. The flux-doubling model overestimates the avalanche rate by about 8%–10%. The properties of the equations describing the avalanche behavior indicate a nonlinear dependence of the avalanche rate on the intensity. The results for fused silica show an almost linear dependence in the high intensity range from about 1 TW/cm2 to infinity, and in the low intensity range up to about 0.01 TW/cm2, but a significant departure from linearity at the intermediate intensities. For a Gaussian pulse, the exponential growth rate of the electron density distribution in the avalanche regime is still almost directly proportional to the instantaneous fluence. Although the proportionality constant increases with increasing peak intensity, the difference is negligible in the high and low intensity ranges.