Laser damage of HR, AR-coatings, monolayers, and bare surfaces at 1064 nm

Laser induced damage thresholds and morphologies have been investigated in a variety of uncoated and coated surfaces including monolayers and multi-layers of different chemical compositions. Both antireflective (AR) and highly reflective (HR) were tested. Testing was done at 1064 nm with 25 picosecond and 8 nanosecond YAG:Nd laser single pulses. Spot diameter in the experiments varied from 0.09 to 0.22 mm. Laser damage measurement procedure consisted of 1-on-1 (single laser pulse in the selected site) and N-on-1 experiments including repeated irradiation by pulses of the same fluence and subsequently raised from pulse to pulse fluence until damage occurred. The highest picosecond damage thresholds of commercially available coatings averaged 12 - 14 J/cm2, 50% less than thresholds obtained in bare fused silica. Some coatings and bare surfaces revealed a palpable preconditioning effect (an increase in threshold of 1.2 to 1.8 times). Picosecond and nanosecond date were compared to draw conclusions about pulsewidth dependence. An attempt was made to classify damage morphologies according to the type of coating, class of irradiating, and damage level.