Abstract
Laser-induced bulk damage in fused silica is studied on a large-aperture laser system with 6 J/cm2, 5-ns shot sequences at 351 nm. The lateral dimension of bulk damage is found to propagate exponentially with shot number in a wide range of growth rates, similar to the stochastic trend as displayed by rear-surface damage. Resemblance in the morphology between bulk and surface damage is revealed offline by microscopic observations. Arising from the accumulated effect of fluence variation, the repetitive laser exposures tend to create an increased number of bulk damage, the tendency of which is applied to evaluate the number of damage initiations via simulations.
Highlights
Due to its high transparency and damage resistance in the ultraviolet regime, fused silica has been widely used in fusion-class laser facilities as the final optical elements, including a considerable ensemble of large-aperture focus lenses, diffraction gratings and windows.[1,2] Under 1-20 ns, 6-8 J/cm[2] irradiation at 351 nm, laser-induced damage in these silica components remains a major concern as the consequent deterioration could hinder the output capability of the entire system
The evolution regularities of laser-induced bulk damage in a large-aperture fused silica have been investigated with full-sized laser sequences at 351 nm
Sharing a typical molten and fractured morphology, bulk damage is found to respond to laser irradiation in an overall similar manner to the surface damage
Summary
Due to its high transparency and damage resistance in the ultraviolet regime, fused silica has been widely used in fusion-class laser facilities as the final optical elements, including a considerable ensemble of large-aperture focus lenses, diffraction gratings and windows.[1,2] Under 1-20 ns, 6-8 J/cm[2] irradiation at 351 nm, laser-induced damage in these silica components remains a major concern as the consequent deterioration could hinder the output capability of the entire system. Bulk damage is a critical limitation to the lifetime of fused silica as it rules out most mitigation techniques designed for the recycle strategy.[3] Fundamental knowledge of the relevant damage performance is important for the development of large high-power lasers. The initiated damage sites on both surfaces of fused silica have been commonly observed to increase and grow rapidly to the millimeter scale by subsequent laser exposure, giving rise to undesirable reduction of optical transmittance and thereby severe degradation of beam quality.[9,10] As for bulk damage, the number and size of such damage category are of particular research interest as well considering the similar effect of deterioration to the lifetime of silica glass. To establish and improve the knowledge-based techniques of damage management, it is necessary to investigate the growth rules of bulk damage in fused silica
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