Defect analysis of UV high-reflective coatings used in the high power laser system.

By considering the rapid change of standing-wave electric-field and assuming the interface defect distribution, an improved model is developed to analyze the defect density distribution and assess the damage performance of high-reflective coatings. Two kinds of high-reflective coatings deposited by e-beam evaporation (EBE) and ion beam sputtering (IBS) techniques are analyzed with this method. The lower overall damage threshold is the major feature for the coatings deposited by IBS method according to the defect parameters extracted from the model. Typical damage morphologies of coatings are also measured and analyzed. The assumption of interface defects is supported by the damage behavior. The damage mechanisms of two high-reflective coatings are attributed to the formation of molten pool and mechanical ejection. The influence of the incident angle on the damage probability is also considered and numerically calculated. The defect analysis model improved here is suitable for high-reflective coatings.