Influence of substrate cleaning on the laser resistance of antireflective coatings

Several studies have reported on the detrimental effects of inadequate cleaning on the performance of optical components exposed to laser radiation. The remaining particulates, contaminants or residue located in the coating or on the substrate surface can absorb laser energy and consequently induce damage. To minimize these contaminants, investigations of various cleaning processes have been performed in both the research and industry communities. Transparent published results and comparisons of the different cleaning processes considered, however, are limited due to proprietary considerations. In addition to this, the manufacturing environment, deposition processes, substrate- and deposition materials all have an influence on the effectiveness of a cleaning process. The purpose of this study was to investigate different cleaning procedures and their influence on the laser resistance of ion-beam sputtered antireflective coatings. For this purpose, a SiO2 / Ta2O5 multilayer antireflective coating for a normal angle of incidence at 1064 nm was deposited onto fused silica substrates. Prior to deposition, the substrates were cleaned with a variety of cleaning solutions and procedures and their roughness and surface quality inspected. All samples were characterized in terms of their laser damage threshold using a 1064 nm ns-pulsed test bench and subsequently visually inspected in order to understand the cause of the damage. In this work, the details of the cleaning steps and the corresponding laser damage performance for the different cleaning processes are presented and compared.