Diffraction gratings for high power lasers: from focusing gratings to quarter-wave metasurfaces

High-power laser systems use hundreds to thousands of large optical components to amplify, filter, transport, sometimes compress and/or frequency-convert, and focus laser beams. Most of these optics are dioptric optical components: mirrors, lenses, windows, laser slabs, crystals, ... Apart from the iconic example of the compression gratings used in the chirped pulse amplification, the use of diffractive optics and in particular transmission gratings is relatively limited. Here we detail the development we carried out to use transmission grating for beam steering and focusing laser beams of the Megajoule laser (LMJ). We describe our early attempts, the first prototype, and the performances finally reached to equip the 176 laser beams of the LMJ. We follow this path by extending the implementation of transmission gratings for beam steering and focusing to the manipulation of the polarization state of highly energetic laser beams. We detail the design and performance of nanostructured silica for achieving linear-to-circular polarization conversion. This full-silica meta-optics acts as a quarter waveplate operating in the UV frequency range at the wavelength of 351 nm. In addition to its effect on polarization, we show how this meta-optics can be used to push back the Kerr filamentation threshold occurring in components of these high-power lasers.