The influence of dynamical change of optical properties on the thermomechanical response and damage threshold of noble metals under femtosecond laser irradiation

TL;DR

This paper presents a theoretical model showing how the dynamic optical properties of noble metals under femtosecond laser pulses significantly influence their thermomechanical response and damage thresholds, with implications for laser micromachining.

Contribution

It introduces a comprehensive theoretical framework that accounts for the time-dependent optical properties and relaxation processes affecting noble metals during ultrashort laser irradiation.

Findings

Dynamic optical properties significantly alter thermal effects.

Consideration of optical property changes predicts lower damage thresholds.

Stress increases notably when optical dynamics are included.

Abstract

We present a theoretical investigation of the dynamics of the dielectric constant of noble metals following heating with ultrashort pulsed laser beams and the influence of the temporal variation of the associated optical properties in the thermomechanical response of the material. The effect of the electron relaxation time on the optical properties based on the use of a critical point model is thoroughly explored for various pulse duration values (i.e. from 110fs to 8ps). The proposed theoretical framework correlates the dynamical change of optical parameters, relaxation processes and induced strains-stresses. Simulations are presented by choosing gold as a test material and we demonstrate that the consideration of the aforementioned factors leads to significant thermal effect changes compared to results when static parameters are assumed. The proposed model predicts a substantially smaller damage threshold and a large increase of the stress which firstly underlines the significant role of the temporal variation of the optical properties and secondly enhances its importance with respect to the precise determination of laser specifications in material micromachining techniques.