Stress field after femtosecond laser interaction with Nd3+ doped Mg: LiNbO3 crystals for waveguides fabrication

M TEJERINA AND GTORCHIA

Playa del Carmen

Conferencia; 11° International Conference on Laser Ablation (COLA 2011); 2011

In this paper we present the development of an open code (?MATFESA?) based on 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. As it is well known, waveguides fabricated by this experimental procedure have compression and tensile regions surrounding to the inscribed laser tracks. The fs-laser pulses residual stress control is the key to obtain high performance guiding structures for photonics applications (i.e. low propagation losses and high refractive index contrast).The whole complex physical problem consists in almost three steps inside the material during/after femtosecond laser interaction which can not be analyzed using thermodynamic equilibrium equations. These are: ionization, expansion and re-solidification. That is why empirical and computer aided iterations are commonly used to analyse the process. In this sense, the code presented in this work is very useful because it makes that analysis easier. 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. As it is well known, the refractive index field can be retrieved from the strain field. 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. Finally, as an important example, the mentioned code was implemented to analyze type II guiding structures generated in Lithium Niobate crystals by fs laser writing.