Thermo-elasto-plastic simulations of femtosecond laser-induced structural modifications: application to cavity formation in fused silica

TL;DR

This paper presents a 2D thermo-elasto-plastic simulation model for femtosecond laser-induced modifications in fused silica, predicting cavity formation and potential crack regions, aiding nano-structure design.

Contribution

It introduces a novel 2D hydrodynamic model incorporating thermo-elasto-plastic behavior to predict laser-induced structural changes in fused silica.

Findings

Warm dense matter relaxation causes shock and rarefaction waves.

Permanent deformations occur when stress exceeds yield strength.

The model predicts cavity formation and crack-prone regions.

Abstract

The absorbed laser energy of a femtosecond laser pulse in a transparent material induces a warm dense matter region which relaxation may lead to structural modifications in the surrounding cold matter. The modeling of the thermo-elasto-plastic material response is addressed to predict such modifications. It has been developed in a 2D plane geometry and implemented in a hydrodynamic lagrangian code. The particular case of a tightly focused laser beam in the bulk of fused silica is considered as a first application of the proposed general model. It is shown that the warm dense matter relaxation, influenced by the elasto-plastic behavior of the surrounding cold matter, generates both a strong shock and rarefaction waves. Permanent deformations appear in the surrounding solid matter if the induced stress becomes larger than the yield strength. This interaction results in the formation of a sub-micrometric cavity surrounded by an overdense area. This approach also allows one to predict regions where cracks may form. The present modeling can be used to design nano-structures induced by short laser pulses.