Laser conditioning of optical thin films

Results are presented that show the damage thresholds of e-beam deposited multi- layer HfO2/SiO2 thin films can be permanently increased by a factor of 2 to 3 by illumination with subthreshold fluences of laser light. This sub-threshold illumination procedure is referred to as "laser conditioning". The films used in this study were prepared by three different physical-vapor-deposition techniques: ion-beam sputtering, plasma plating and e- beam evaporation. Only the e-beam deposited films showed consistent and significant improvement with laser conditioning. Of the material pairs examined (Hf02/Si02, ZrO2/SiO2 and TiO2/SiO2), Hf02/Si02 gave the greatest and most consistent damage improvement with conditioning. The number of layers and the reflective or transmissive characteristics of the HfO2/SiO2 films were found to have little` impact on laser conditioning of the film. The results show that the damage thresholds of a wide range of e-beam deposited coatings (e.g. HR's, polarizers, etc.) can be improved by laser conditioning. Several possible conditioning mechanisms are examined.