We have performed simulations of laser energy deposit in sub-micrometric spherical defects and the surrounding fused silica. We have studied crater generation produced by the absorber explosion with a 2D/3D Lagrange-Euler code taking into account crack formation and propagation in the brittle material. The comparison of the 2D simulations with experiment shows quite good agreement for shallow defects (depth < 2 μm). We have observed experimentally that the explosion of deeper absorbers results in a more complex crater morphology. Therefore we have begun performing 3D simulations in order to reproduce these features.
Depending on the defect depth, the cracks may not reach the surface and a crater doesn't appear. Nevertheless, those cracks or pre-existing cracks can contribute to efficient electric field enhancement and breakdown on the surface. Different types of cracks (size, inclination, filled with a material or not) were investigated and the 2D or 3D electromagnetic field distributions were computed using a finite element code.
The validation of numerical simulations of laser induced damage of fused silica requires detailed knowledge of the different parameters involved in the interaction. To approach the problem, we have performed simulations of laser energy deposition in spherical metallic defects and the surrounding fused silica. Our code DELPOR takes into account various laser/defect induced absorption mechanisms of SiO2, such as radiative ionization, avalanche and multiphotonic ionization. We have studied crater formation produced by the absorber explosion with a 2-D Lagrange-Euler code taking into account crack formation and propagation in the brittle material. To validate our simulations, we have made and tested samples of ultra-pure silica thin film, containing gold nanoparticles of diameter 0.6 μm. The fused silica coating could have three different thickness. We compare experiment and simulations for two laser irradiations at wavelengths 0.351 and 1.053 μm.
Simulations of laser-fused silica interactions at 0.351 μm are a key issue in predicting and quantifying laser damage in large laser systems such as LIL and LMJ. Validation of numerical simulations requires detailed knowledge of the different parameters involved in the interaction. To concentrate on a simple situation, we have made and tested a thin film system based on calibrated gold nanoparticles (0.2-0.8 μm diameter) inserted between two silica layers. The fused silica overcoat was either 2 or 10 microns thick. We have performed simulations of laser energy deposition in the engineered defect (i.e. nanoparticle) and the surrounding fused silica taking into account various laser/defect induced absorption mechanisms of SiO2 (radiative ionization, avalanche and multiphotonic ionization). We have studied crater formation produced by the absorber explosion with a 2D Lagrange-Euler code taking into account crack formation and propagation in the brittle material. We discuss the influence of the defect depth (with respect to the surface) on the damage morphology. The simulations are compared with our experimental results.
The purpose of this paper is to present the effect of a spherical inclusion in SiO2 under pulsed laser irradiation. The 3D electromagnetic field distribution (E, B) in the inclusion and the SiO2 bulk is calculated using the Mie theory extended to radially inhomogeneous media. The effects of electric field enhancement can be investigated for any size and any type (metallic or dielectric) of inclusion. This E-field enhancement may lead to direct breakdown of SiO2. The laser energy coupled with the inclusion and the host material is computed with the numerical code DELPOR along the laser duration. DELPOR is a 1D hydrodynamic code used for spherical geometry taking into account the laser solid- to-plasma interaction, thermal diffusion and phase transitions. During the laser pulse, the 1D hydrodynamic calculation is coupled with a 3D Lagrangian-Eulerian code to investigate the mechanical effects involved in the blow-up of the inclusion near the SiO2 slab surface. For a set of experimental conditions, we attempt to determine the role of mechanical effects and E-field enhancement. Our ultimate goal is to predict laser damage morphology as a function of the physical and geometrical parameters (inclusion type, size and depth) of the inclusion and to compare it with experimental data.