Influence of defect removal on the optical properties of multilayer dielectric gratings during magnetic compound fluid polishing

Abstract

The fabrication of multilayer dielectric gratings (MDGs) is a complex process that frequently results in microstructural defects, which can significantly degrade the performance of high-power laser systems. Magnetic compound fluid (MCF) post-processing has been shown to effectively mitigate these defects, reduce surface roughness, and improve the laser-induced damage threshold (LIDT) of MDGs. Through numerical simulations, the influences of defect removal depth on the optical performance of two common MDG types are studied. For ps-MDGs with a central wavelength of 1053 nm, it is found that maintaining defect depth below one-tenth of the grating ridge height preserves the optical performance after MCF treatment. Similarly, for fs-MDGs centered at 800 nm, keeping the defect depth below one-eighth of the grating ridge height ensures their suitability for pulse compression following MCF treatment. The study further examines the relationship between grating structural parameters and the allowable polishing removal depth, providing essential insights for optimizing MCF polishing processes to address microstructural defects in MDGs.