Interfacial effects on the transient temperature rise of multilayer coatings induced by a short-pulse laser irradiation

Multilayer optical thin film coatings are typically based on quarterwave design using alternating high- and low-index materials. The standing wave within these multilayer coatings introduces peaks of electrical field at the interfaces between the high- and low-index materials, which makes the interfaces potentially weaker parts in terms of laser damage resistance. The possible interfacial absorption and thermal resistance will further weaken these interfaces and make them prone to laser induced damage. In this paper a numerical model is developed for analyzing the interfacial effects on the transient temperature rise of multilayer coatings induced by a short pulse laser irradiation. The parameters studied include coating design, thermal physical properties of thin films, and interfacial absorption and thermal resistance. It is found that by choosing an appropriate coating design and eliminating the interfacial effects, the laser induced peak temperature rise of multilayer coatings can be drastically reduced. Examples are presented for both quarterwave and non-quarterwave HfO₂/SiO₂ high reflectivity coatings.