106-μm laser damage of optical coatings: regression analyses of round-robin test results

Abstract

The laser-induced damage thresholds of four different coating designs obtained with three to six samples each at eight laboratories involved in a round-robin experiment were evaluated by means of multiple regression analyses for the two main independent parameters: pulse width τ and beam diameter d [ K. H. Guenther , Appl. Opt.23, 3743 ( 1984).] The analyses show that the F vs τ1/2 relationship, with F being the damage threshold energy density (J/cm2) known from other experiments also holds for this one. The F vs d−m scaling law, however, yields only rather weak powers of m = 0.015–0.2 for Fmin(D) (the minimal energy density threshold causing damage) and m = 0.06–0.5 for Fmix(ND) (the maximum energy density threshold for which no damage is observed). This is in contrast to the previously established scaling laws of d−1 or d−2. The results are discussed in terms of defect density, which was checked for a number of samples with distribution plots taken from optical micrographs of undestroyed portions of the coating.