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GRATING DEVELOPMENT

To develop petawatt-class lasers beyond their current state, compression gratings are required which can support higher energies than the currently available gold gratings. A petawatt-class grating must be vacuum-compatible with large-aperture while having a high laser damage threshold, high diffraction efficiency, and the appropriate dispersion. As these qualities drive costs, end users would prefer the solution to be both producible and relatively cost effective.

The popular approach to the problem has been to develop multilayer dielectric gratings (MLD) within the short-pulse laser community. This option essentially etches a binary phase grating into the top layer (usually fused silica) of a dielectric mirror. These new MLD gratings offer the potential for higher efficiency and higher damage threshold, but optimization of these and other parameters is under way with a few vendors/researchers. We have had and will continue to have collaborative efforts with these groups.

One avenue explored at Sandia has been the option of replacing the etched binary phase grating of the MLD with a volume phase grating to create a mirror-backed volume phase grating; ref.: Rambo (2005). Gelatin-based materials like sol-gel or dichromated gelatin can coat large areas, are vacuum compatible, and do not require large aperture etching since the grating structure is created by modifying the material index via light exposure.

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