We report on the implications that the temporal and spatial beam metrologies have on the accuracy of temporal scaling laws of Laser Induced Damage Threshold (LIDT) for dielectric materials in the picosecond regime. Thanks to a specific diagnostic able to measure the temporal pulse shape of subpicosecond and picosecond pulses, we highlight through simulations and experiments how the temporal shape has to be taken into account first in order to correctly understand the temporal dependency of dielectrics LIDT. This directly eases the interpretation of experimental temporal scaling laws of LIDT and improves their accuracy as a prediction means. We also give numerically determined benchmark temporal scaling laws of intrinsic LIDT for SiO2 (thin film) based on the model developed for this work. Finally, we show as well what kind of spatial metrology is needed during any temporal scaling law determination to take into account potential variations of the spatial profile.
A technique that provides quantitative and spatially resolved retardance measurement is studied for application to laser-induced modification in transparent materials. The method is based on the measurement of optical path differences between two wavefronts carrying different polarizations, measured by a wavefront sensor placed in the image plane of a microscope. We have applied the technique to the investigation of stress distribution induced by CO2 laser processing of fused silica samples. By comparing experiments to the results of thermomechanical simulations we demonstrate quantitative agreement between measurements and simulations of optical retardance. The technique provides an efficient and simple way to measure retardance of less than 1 nm with a diffraction-limited spatial resolution in transparent samples, and coupled to thermomechanical simulations it gives access to birefringence distribution in the sample.
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