Asymmetric interactions induced by spatio-temporal couplings of femtosecond laser pulses in transparent media

Abstract

Numerous experimental studies in recent years have revealed intriguing symmetry breakings during non-linear interaction of ultrashort laser pulses with materials. Dependence of the formed structures on the direction of laser scanning and polarization, an effect known as non-reciprocal writing, is one of the most commonly observed asymmetries. These observations are generally attributed to spatio-temporal couplings (primarily pulse-front tilt) in the laser pulses. Even though such couplings indeed break the spatial symmetry of the light–matter interactions, a detailed understanding of ongoing phenomena in the microscopic level is still lacking. In this work, we present our theoretical results, which, to the best of our knowledge, constitute the first demonstration of the physical mechanisms behind non-reciprocal writing and related effects in transparent media. Our model is based on non-linear Maxwell’s equations supplemented by the hydrodynamic equations for free electron plasma, and rate equations for the evolution of defects inside the material. It has enabled us to gain a qualitative insight into the features of propagation of ultrashort laser pulses with tilted pulse fronts, in the regimes of volumetric laser modification of transparent materials.