Surface modifications induced by the laser ablation of surface-bound microparticles at low to moderate fluence level in the ultraviolet

This study investigates the surface modifications on fused silica caused by the ablation of glass and aluminum micro-particle contamination exposed to laser shots at a wavelength of 351 nm. The laser fluences used in this study range from 3.5 to 9.4 J/cm² with a pulse duration of 3 ns. The study establishes a proportionality relationship between the size of the particle and the size of the crater formed by the particle ablation on the substrate. The relationship is influenced by the nature of the particle and the level of fluence. Quadriwave lateral shearing interferometry (QLSI) microscopy is used to acquire high-resolution phase shift and amplitude maps of the surface modifications. The measurements demonstrate that the combination of particle type and fluence level can result in different amplitude and phase surface modifications. Diffraction modeling using QLSI data is used to quantify the light intensification induced by these bound-particle laser damage sites. Aluminum particles can produce light intensification as high as 4.5x in the first centimeter after the surface, while glass particles exhibit shallow intensification. The study also reveals that in the fluence range of 5 to 8 J/cm², there is a widely dispersed behavior for aluminum particles, leading to different phase/amplitude distributions at the damage sites. This mixed behavior can result in high intensification despite the moderate laser fluence level initiating the damage site.