Numerical study of laser radiation propagation in powder media
V.V. Lisenkov, V.V. Platonov, E.V. Tikhonov
Institute of Electrophysics, Ural Branch of the Russian Academy of Sciences, Ekaterinburg, Russia
Keywords: radiation propagation, Helmholtz equation, impact ionization, electron diffusion, Boltzmann equation
Abstract
Micropowders made of transparent semiconductor and dielectric materials (ZnSe, MgF2, CaF2, SiO2, BaF2, MgAl2O4, Al2O3, Nd:Y2O3, YSZ, and TiO2) are theoretically studied. The refractive indices of these materials are in the range 1.38 ¸ 2.48. As a result of calculations, it is found that the combination of scattering and interference of radiation increases its intensity by one or two orders of magnitude compared to the intensity of the incident radiation in a medium of particles several microns diameter. It is shown that this enhancement increases with the refractive index of the particle material. In our opinion, both nonlinear mechanisms of laser radiation absorption and avalanche ionization lead to an increase in the electron concentration in such local maxima. As a result, the material begins to heat up to the point of ablation.
|
