Continuous-wave and femtosecond lasers inscriptions on amorphous silica glass

Abstract

This thesis proposes a theoretical approach to explore the e ects of the competition between multi-photon absorption, group-velocity dispersion and electron-hole radiative recombination processes, on the laser beam dynamics (i.e. continuous-wave and femtosecond regimes) and stability (spot) during inscription on amorphous silica glass. The study rests on a model consisting of a K-order nonlinear complex Ginzburg-Landau equation, coupled with a Drude-type equation for the electron plasma density. In this goal, the modulational instability analysis combined with the dynamical approach was used to explore all the possible operation regimes inherent to the stability of the model. For the modulational instability analysis, we have considered a single input laser intensity in the continuous wave regime then we started the analysis from an input eld in the steady state, and followed its stability when coupling a small perturbation with the laser amplitude as it propagates in an anisotropic transparent amorphous silica glass. An analysis of the stability of continuous-waves regime, following the modulational-instability theory, reveals that, in the absence of electron-hole radiative recombination, the competing e ects of Kerr nonlinearity and K-photon absorptions can stabilize or destabilize the continuous wave laser beam during the inscription process. However, in the presence of electron-hole radiative recombination, our analysis of stability of continuous-waves regime, following the modulational-instability, suggests that the competitions between multiphoton absorption and radiative recombination processes can be detrimental or favorable to continuous-wave laser stability, depending on the group-velocity dispersion of amorphous silica glass. In the full nonlinear dynamical regime, we have chosen a speci c ansatz (to represent a femtosecond laser) that we introduced in the model and this allows us to transform the system of model equations into a system of four equations of rst order (ODE's) for which we examined its singular solutions by exploring the possible xed points, as a function of the multi-photon absorption rate K. Then, we proceeded numerically to solve the system of four equations of rst order ordinary di erential equation (ODE's), using a fourth-order Runge- Kutta algorithm. Numerical simulations of the full nonlinear regime reveal the existence of the stable pulse trains for which the amplitudes are increased by the radiative recombination processes. From these last results, we were able to derive the femtosecond laser beam spot diameter dspot = 50 m that could allow to obtain a ne engraving on amorphous silica glass.