Absorptance behavior of optical coatings for high-average-power laser applications

A modified photothermal deformation technique is used to measure the absorp tance behaviors of optical multilayered dielectric coatings for a high-powe r laser system. The surface thermal-lensing modification uses an enlarged. probe beam to facilitate alignment of the laser beam and data acquisition. The coatings, both reflective and transmissive types, are made by a physica l vapor-deposition process. Coating absorptances are observed to depend on the laser's exposure time and power density. Time-dependent absorptance def ect models are proposed. Also, micrometer-sized sites of high absorptance a nd an area with physical damage can be found during the spatial scans. It i s proposed that absorptance values reported for coatings in high-repetition -rate or cw-laser systems include time- and power-dependent behaviors in ad dition to other relevant irradiation parameters. (C) 2000 Optical Society o f America.