title: Absorptance behavior of optical coatings for high-average-power laser applications.
abstract: A modified photothermal deformation technique is used to measure the absorptance behaviors of optical multilayered dielectric coatings for a high-power 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 physical vapor-deposition process. Coating absorptances are observed to depend on the laser's exposure time and power density. Time-dependent absorptance defect models are proposed. Also, micrometer-sized sites of high absorptance and an area with physical damage can be found during the spatial scans. It is proposed that absorptance values reported for coatings in high-repetition-rate or cw-laser systems include time- and power-dependent behaviors in addition to other relevant irradiation parameters.
authors.affiliation: Lawrence Livermore National Laboratory, University of California, Livermore, California 94550, USA. chow3@llnl.gov
authors.forename: R
authors.initials: R
authors.lastname: Chow
authors.forename: J R
authors.initials: JR
authors.lastname: Taylor
authors.forename: Z L
authors.initials: ZL
authors.lastname: Wu