Research On Damage Repair Shape Design Of Fused Silica Components That Suppresses The Enhancement Effect Of Light Field Modulation

As the basic material of focus lens and diffractive optics, fused silica is extensively used in the laser drivers for Inertial Confinement Fusion (ICF). For these high-power UV laser drivers, one of the key problems limiting the maximum light influence and safe routine operation is the UV laser-induced damage of fused silica optics. At present, the most effective mitigation protocol of the damaged optics is the CO2 laser processing technique to locally melt or evaporate the damage, which is important to ensure the fluence level and prolong the life-time of the component. However, perturbations from flat to the optical surface profile following the CO2 laser processing can induce ripples in the phase of the propagating laser beam, causing some amount of downstream intensity modulation with the potential to ruining the neighbor optics.Based on the scalar diffraction theory, the dissertation focuses on the morphological design of mitigatied sites from numerical simulation and experimental investigations to avoid the downstream intensification ruining the neighbor optics. The morphology features of the mitigated damage sites of fused silica optics were systematically experimentally investigated, and the relationship between morphology features and downstream intensification were given. The results of this research indicate that the downstream intensification of mitigated sites can be suppressed by controlling the morphology features of mitigated sites, which is significant for the development and improvement of the mitigated techniques of damage optics. The investigation contents and results of this dissertation are summarized as follows:1. The morphology of non-evaporation mitigatied sites were systematically investigated by using optical microscope, WYKO white light interferometers, and XP-200 stylus profilometer. According to the measured morphology features, a 3D grid model of mitigated sites was built, which surrounded by a raised rim around the mitigated sites, to model the downstream intensification. Through the numerical simulation and experimental investigations, the relationship between morphology features (height, diameter, the height and location of surrounding rim) and downstream intensification were given. The results indicate that there are two kinds of downstream intensification:off-axis and on-axis intensifications. For the off-axis intensification, the maximum intensity locates near the output surface of optics and mainly relies on the depth of the mitigated sites, and will increase with deepening depth. For the on-axis intensification, the maximum intensity locates far from the output surface of optics and is mainly dependent on the height of the rim structure on the fringe of the mitigated sites, and will increase with increasing height.2. Acording to the characteristic of the evaporative mitigation processing, three different kinds of mitigated site morphology models were built, and the downstream modulation effects of different kinds of mitigation sites models on transport of laser beam (351 nm) were studied by using scalar diffraction theory and Fast Fourier Transform (FFT) methods. the results indicate that the parabolic mitigated sites will be the best choice for mitigated morphology with the same height and diameter of different kinds of mitigation sites3. A tightly-focused 10.6?m CO2 laser spot is scanned over the mitigated sites to study the effect of the second mitigation processing on downstream intensification. The results indicate that the second mitigation processing is beneficial for controlling the location of maximum modulated intensity to avoid the downstream intensification ruining the neighbor optics.