Defect geometries and laser-induced damage in multilayer coatings

A correlation between laser-induced damage and the height of a coating defect was found from an examination of HfO2/SiO2 mirrors made by three different coating vendors. The nodular defects in these reactive e-beam deposited mirrors were studied using the combination of SEM, optical microscopy, FIB and AFM techniques. Each vendor had small defects in common, but characteristically different large defects. Also the majority of seeds that caused the defects were made of hafnia, not silica. The apparent mechanical stability of the defects within the coating plays a major role in the laser resistance (1064 nm and l0ns) of a high damage threshold coating