MATFESA: Strain and refractive index field estimation after femtosecond laser interaction with transparent material

Abstract

In this paper we present the development of an open code ("MATFESA") based on the Finite Element Method (FEM) which can be used to estimate the strain and refractive index fields after femtosecond laser writing process by means of an iterative analysis. The fs-laser pulse residual stress control is the key to obtain high performance guiding structures for photonics. The whole complex physical problem consists in almost three steps inside the material during/after femtosecond laser interaction which cannot be analyzed using thermodynamic equilibrium equations. These are: ionization, expansion and re-solidification. In the numerical model solved, a mechanical expansion is introduced in the focal plane to simulate laser interaction at intensities above the optical breakdown threshold. Numerical results were compared to experimental measurements of optical guided modes in LiNbO 3 fs-waveguides. The MATFESA model was compared with ABAQUS commercial software in order to verify the strain field results and also to test the 2D, plane strain approximation. © Springer-Verlag 2012.