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Comparative study of IR and UV laser damage resistance of silica thin films deposited by electron beam deposition, ion plating, ion assisted deposition and dual ion beam sputtering

The laser damage resistance of optical coatings is a critical point for a large number of applications. However improving this resistance is often hard to obtain because of the large number of parameters in the deposition processes than can modify the laser damage threshold and the lack of detailed and exploitable studies published on this subject. Then, the aim of this work is to test and analyze the laser damage resistance of a usual material for high power applications (silica) deposited in various conditions. The thin films of different thicknesses were specially deposited using different techniques available at the Institut Fresnel: Dual Ion Beam Sputtering, Electron Beam Deposition, Ion Assisted Deposition and Ion Plating. The laser-induced damage thresholds of these coatings were determined at 1064nm and 355nm using nanosecond pulsed YAG lasers, with a 1-on-1 test procedure. Other diagnostic tools were used to complete the study and make potential correlations with laser damage: photothermal techniques, luminescence spectrocopy, optical profilometry, dark field and Nomarski microscopy. The comparative study of these results highlight different laser damage behaviors of the silica coatings that we correlate to the density and the nature of the defects.