LIDT measurement routine to assist coating optimization studies of low defect density optics in the nanosecond pulse regime

A combined laser-induced damage threshold (LIDT) measurement routine is presented specifically for optics, which are subject of further optimization to nanosecond fusion laser optics. By extending a raster scan method with an R(S)-on-1 routine that has a last intact spot damage criterion, not only the current LIDT limited by the most critical defect is measured but also up to the intrinsic LIDT of the coating. This demonstrates how existing routines can be combined to distinguish between a defect-driven and an intrinsic damage threshold. During coating optimization studies, this allows to correlate specific coating process parameters directly to their influence on both the defect-driven and the <b>intrinsic</b> LIDT of the coating. A high-quality in situ microscopic imaging during the measurement routine is essential for the precise LIDT evaluation, and combined with high-precision ex situ measurement techniques, it allows an even more detailed investigation of participating damage mechanisms. An exemplary cross-sectional microstructure damage analysis showed that observed changes in color can be linked to a local delamination of the coatings top layer and a change in reflectivity.