Light scattering from laser-induced shallow pits on silica exit surfaces

We study the formation of laser-induced shallow pits (LSPs) on silica output surfaces and relate these features to optical performance as a function of incident laser fluence. Typical characteristics of the LSPs morphology are presented. Closed-form expressions for the scattered power and far-field angular distribution are derived and validated using numerical calculations of both Fourier optics and FDTD solutions to Maxwell's equations. The model predictions agree well with the measurements for precise profile micro-machined shallow pits on glass, and for pitting caused by laser cleaning of bound metal micro-particles at different fluences.