Understanding Femtosecond Laser Modification of Bulk Dielectrics

Abstract

The minimum spacing of a plasma waveguide was calculated and applied to the formation of periodic nanocracks. The minimum spacing decreased with decreasing plasma frequency but was found to have limited effect on the spacing of the nanocracks. An extension to a standard Finite-Difference Time-Domain method was created to include nonlinear processes and the dynamic build up of the electron plasma. The ionized area produced in the simulation agrees with experiment. The existence of a self-limited absorption effect on a Gaussian pulse in time was verified in the simulations. The region was elongated along the direction parallel to the polarization of the light. The multiphoton absorption was found to be the main cause of the distinct shape of the damaged area. Plasma dispersion and self-focusing create larger electron densities and a shift in the location of the electron density peak, but did not affect the general shape.