Damage threshold investigations of high-power laser optics under atmospheric and vacuum conditions

Abstract

In many cases, optical coatings are the limiting factor for the operational reliability of measurement systems and other technical devices based on laser irradiation. Especially in space applications, the reliability of an optical system is of existential importance. In this context, the behavior of the laser induced damage threshold (LIDT) in vacuum and in atmospheric pressure is of major interest. Initial experiments have shown a loss of performance of coatings that were exposed to vacuum conditions. On the one hand the LIDT at the fundamental wavelength of the Nd:YAG laser (1.064 µm) was determined, and on the other hand damage threshold investigations at the third harmonic of 355nm were performed on equivalent coatings. Compared to normal atmospheric conditions, significantly different spectral characteristics were observed for dielectric coatings, which were produced by various coating processes (electron beam evaporation, ion assisted deposition (IAD) and ion beam sputtering (IBS)), under vacuum. In the present paper the damage mechanisms in the ns range are investigated against the background of the experimental results attained for the different environments.