Characterization of absorptance homogeneity in thin-film coatings for high-power lasers by thermal lensing microscopy

Abstract

A focus error method photothermal microscope was designed for the characterization of absorptance homogeneity in thin-film coatings for high-power lasers. The technique relies on the detection of the thermal lens induced by the local absorption of a light power focused laser. The detailed design of the instrument is presented. The resolution of the system is better than 0.1 ppm and allows the realization of spatial sweeps and even measurements of the evolution of absorption as a function of time with a spatial resolution of 1 μm. These capabilities allow the location of defects and their characterization.