Theoretical study of spatiotemporal focusing for in-bulk laser structuring of dielectrics

Abstract

For laser processing applications and creation of microstructures inside dielectric materials, focusing of a femtosecond Gaussian pulse within the bulk of these materials is commonly used. The laser energy is mainly absorbed in the focal spot due to the nonlinear feature of laser–dielectric interaction. Recently, to get further control of laser energy absorption, the spatiotemporal focusing technique, for which the pulse duration evolves in the course of propagation, has been introduced. However, spatiotemporal focusing also leads to an inclination of the wavefront, the pulse-front tilt. In this work, the influence of the pulse-front tilt on pulse propagation and interaction is studied by solving numerically the Maxwell’s equations coupled to laser induced electron dynamics in dielectrics. The qualitative behavior of energy absorption, and geometric features of the resulting absorption volume are presented. By varying the laser intensity and pulse-front tilt, both the aspect ratio and symmetry of the absorption volume are changed. A simple model predicting the evolution of this aspect ratio is provided.