Abstract

Significant interest continues to be shown in the improvement of the performance of optical coatings destined for high power laser applications. For laser applications, several factors play a role, in particular the effect of thin film microstructure. Many commercial processes rely on the use of electron beam sources. When used for refractory materials, such processes often result in coatings with a significant density of second phase inclusions. The problems arise as a result of non-uniform heating exacerbated by the poor thermal conductivity of the material present in the hearth, giving rise to the ejection of particulates. In addition the strong electrostatic forces within the chamber result in the efficient recirculation of the particles, distributing them around the coating chamber. A number of studies have recently highlighted the role that such defects play in setting the laser damage resistance of optical coatings. The defects have recently been shown [1-2] to act as immersion microlenses, enhancing electric field intensities and energy densities . Coatings with a high resistance to laser induced damage can therefore only be realised when steps are taken to avoid the formation of such defects during film deposition.

© 1995 Optical Society of America