Improvement of the laser-induced damage threshold of oxide/fluoride double stack high reflective coatings at 355 nm by introducing interlayers

The development of oxide/fluoride double stack coatings presented a good solution for the fabrication of HR coatings with high reflectance and low stress. However, their low laser-induced damage threshold (LIDT) remains to be one problem unsolved. In this paper, SiO2 interlayer was introduced into the optimized double stack coatings and a 50% increase in LIDT was obtained. Characterizations including the residual stress, damage crater depth, damage morphology, electric field distribution, and density of surface defects were conducted in order to analyze the mechanism of such improvement. The decrease in density of sensitive defects and the increase in stability of defects are believed to be the benefits brought by the optimized design.