Influence of preparation conditions on the laser damage threshold of oxide thin films at 248 nm measured by photoacoustic mirage detection

Abstract

ABSTRACT The ablation damage thresholds for electron beam evaporated Hf02/Si02 single-, double-, and triple- layer systems of ?J4 optical thickness (X=248nm) are measured by the pulsed photoacoustic miragetechnique. It is shown that the apparent threshold depends on the specific system design and results are interpreted in terms of the electric field distribution in the respective configuration. For one system it is demonstrated that the threshold for the onset of damage measured by the mirage technique can be enhanced by a factor of two when the layers are deposited by laser assisted evaporation technique. 1. INTRODUCTION One of the main limiting factors in improving the output power of high-power lasers is the damage of the optical thin film components. Usually the laser induced damage threshold of optical coatings are lower than those of uncoated surfaces or bulk materials. High melting oxide films are candidate materials for thin film systems because of their good mechanical stability, the generally low toxicity in the deposition process, the good UV transparency andthe relatively high refractive index1.