Sol–gel-processed hybrid silica-PDMS layers for the optics of high-power laser flux systems

Abstract

The laser-induced damage of optical components of high-power laser systems such as the National Ignition Facility (NIF) (Murray, Proc SPIE 3492:1–10, 1998) and Laser MegaJoule (LMJ) (Andre, Fusion Eng Des 44:43–49, 1999) can have a significant impact on the operating costs of these laser systems since optimal shaping to carry out ignition is required. Laser-induced damage (LID) of fused silica appears on the exit surface, mostly at 3ω, and tends to grow exponentially with each laser shot. This damage affects the performance of optical components and limits their lifetime. The damage is due to thermal explosions of microdefects or microabsorbers, and these explosions emit a plasma that generates shock waves introducing cracks that increase the damage. This paper, thus proposes the deposit of an elastic layer on the exit surface to mitigate the shock waves and thereby decrease the extent of the damage volume. To this end, we have developed a mendable sol–gel-processed hybrid inorganic–organic layer. The hybrid layer is a nanocomposite made of silica and polydimethylsiloxane (PDMS). Their resultant mechanical properties can be tuned by adjusting the elastomer/silica ratio and catalysis conditions. The synthesis used to create these layers was investigated with an infrared spectrometer. The optical quality of the hybrid layers was checked by UV/visible/NIR spectrophotometry and thickness uniformity were mapped via reflectometry. Young’s modulus, Poison’s ratio, and the hardness have been measured in order to characterize the mechanical properties of these layers. The surface acoustic waves technique was used to determine Young’s modulus and Poison’s ratio of an optical layer obtained by a sol–gel process. The hardness has been measured with a homemade indenter. The results of first measurements of laser damage made with an excimer laser at 351 and 353 nm demonstrated a reduction of the laser-induced damage threshold with the PDMS/silica ratio.