Abstract
Atomic structural modification and defect processes of fused silica resulting from UV-laser irradiation are studied by a combination of molecular dynamics (MD) simulations and the Reactive Force Field (ReaxFF). Bond state transitions by laser excitation are modeled as the result of localized recoils during energy deposition. Computations of pair distribution functions and bond angle distributions of the irradiated structure reveal that fused silica undergoes significant changes in terms of Si-O, Si-Si pair distances and Si-O-Si bond angles, which are attributed to the formation of silicon and oxygen coordination defects. It is found that nonbridging oxygen is responsible for the decreased Si-O bond length, while laser-induced five-coordinated silicon leads to small Si-O-Si bond angles in 2-membered rings.
Highlights
Excellent transparency and damage resistance in the ultraviolet (UV) region have led to broad applications of fused silica in the final optics assemblies of inertial confinement fusion laser systems, such as the National Ignition Facility in the United States and the Laser Megajoule in France.[1,2] current operational conditions often expose the silica components upstream from the fusion target to nanosecond, 351-nm pulse sequences with fluences near the laser-induced damage threshold, resulting in optical degradations that severely hinder the capability of laser output
Molecular dynamics (MD) simulations were performed to present evidence that silica structure in both short and medium ranges is directly modified by UV-induced defects
The concept of bond breaking is plausibly introduced, which shares similar characteristics to laser-induced radiolysis, the dominant mechanism occurring upon exposure.[9,10]
Summary
Excellent transparency and damage resistance in the ultraviolet (UV) region have led to broad applications of fused silica in the final optics assemblies of inertial confinement fusion laser systems, such as the National Ignition Facility in the United States and the Laser Megajoule in France.[1,2] current operational conditions often expose the silica components upstream from the fusion target to nanosecond, 351-nm pulse sequences with fluences near the laser-induced damage threshold, resulting in optical degradations that severely hinder the capability of laser output. UV-induced modification of fused silica: Insights from ReaxFF-based molecular dynamics simulations
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