Improved Laser Damage Resistance of Multi-Layer Diffraction Gratings Vapor-Treated with Organosilanes

Multi-layer dielectric gratings are used in high power laser systems to compress laser energy pulses. The final power of these short pulse petawatt class systems is limited by the laser damage resistance of the optical components in the system, especially the diffraction gratings. This work was motivated by the previous discovery that vapor-treatment of gratings with hexamethyldisilazane (HMDS) can increase the damage threshold. Gratings were laser damage tested, and then a simple room temperature vapor-deposition technique was used to coat them with several different disilazane compounds. The gratings were then damage tested again to determine if an increase in damage threshold had occurred. The laser-induced damage threshold of an HMDS-treated grating increased by 4.5 % in a 1-on-1 damage test, while that of a tetramethyldisilazane-treated grating increased by 16.5 % in an N-on-1 damage test. Both the N-on-1 and 1-on-1 damage thresholds of a bis-(trifluoropropyl)tetramethyldisilazane-treated grating increased, by 4.8 % and 5.3 % respectively. Such increases in laser damage threshold are unprecedented and counterintuitive because it is widely accepted that the presence of organic material or coatings on the surfaces of optical substrates decreases their laser damage resistance. The results are especially encouraging since they were obtained on samples of sub-optimal quality. The next logical step is to attempt to confirm this effect on high-quality, freshly cleaned grating samples. 1