The pulsed laser damage sensitivity of optical thin films, thermal conductivity

Abstract

Pulsed laser induced damage of optical thin films is, in general, initiated by the absorption of laser radiation by imperfections in the films or at interfaces between film layers and/or the substrate. A heat flow analysis of this process stresses the importance that the thermal conductivity of both the thin film host and that of the substrate play in establishing the laser-induced damage threshold. Unfortunately, recent work, which will be reviewed in this presentation, indicates that the thermal conductivity of thin films can be several orders of magnitude lower than that of the corresponding material in bulk form. This situation arises as a consequence of the film structure resulting principally from the deposition process. The importance of thermal conductivity will be compared to parameters such as absorption mechanisms, film materials, composition, and other variables. Its implication for the ultimate optical strength of materials and the direction in which thin film research and processing should proceed will be highlighted.