Abstract

At LLNL we are interested in increasing the damage threshold of optical coatings used in high power laser applications such as Inertial Confinement Fusion. The coating of particular interest is a highly reflective dielectric multilayer mirror (HR) consisting of many alternating quarter-wave layers of HfO₂ and SiO₂ at 1.06μm. Laser induced damage in optical coatings is often associated with structural defects in the films. In dielectric HR coatings the predominant surface defects are μm-scale domes associated with the classic nodule defect. The nodule shape is determined by shadowing effects during the deposition process and can originate at a seed either at the substrate surface of within the film itself. Recent results using Atomic Force Microscopy and conventional Nomarsky microscopy [1] have shown that the nodule defects also control the laser conditioning effect in which the damage threshold of multilayer dielectrics can be increased by factors of 2-3 by post-deposition subthreshold illumination [2].

© 1992 Optical Society of America