Doubling the efficiency of high-resolution X-ray gratings via thin-film interference

We found that the efficiency of high-resolution soft X-ray gratings having a high groove density can be significantly improved by optimization of the thickness of the reflective coating owing to constructive thin-film interference. A 4444 lines/mm blazed grating was fabricated and coated with a regular Cr/Au coating and then with an ultra-thin Cr/Au coating optimized by efficiency simulations. Diffraction efficiency measurements confirmed an almost 100% gain of the diffraction efficiency for a photon energy of 640 eV.