Mechanism of Laser Induced Filamentation in dielectrics

TL;DR

This paper investigates the physical mechanisms behind femtosecond laser filamentation in fused silica, revealing the roles of Kerr nonlinearity and geometrical focusing through advanced simulations and analytical modeling.

Contribution

It provides the first detailed simulation-based analysis of single and multiple laser pulse refocusing and damage zones in fused silica, clarifying the regimes governing filamentation.

Findings

Kerr nonlinearity dominates loose focusing regimes.

Geometrical focusing is key in tight focusing regimes.

Simulation results align with experimental data.

Abstract

Laser filamentation in transparent material has a wide range of applications, from three dimensional manufacturing to biological technologies. Various experimental results showed that femtosecond laser pulse filamentation in fused silica strongly depends on laser focusing conditions. However, the physical mechanism governing each regime has not been fully understood. For the first time, single and multiple re-focusing of the laser pulse in interaction of femtosecond laser pulse with fused silica, and consequent single and multiple damage zones (filaments) have been observed in our extensive three-dimensional, high resolution FDTD (finite-difference time-domain) simulations. We show that Kerr nonlinearity plays a crucial role loose laser focusing regime, while it is not an important factor in tight laser focusing regime, where geometrical focusing becomes important. Our simulation results agree well with existing experimental findings. In addition, the improved analytical model prediction gives a reasonable estimate of the shift from Kerr nonlinearity regime to linear geometrical focusing regime.