Holographic diffraction gratings generated by aberrated wave fronts: application to a high-resolution far-ultraviolet...

We investigated the ability of aberration-corrected concave holographic gratings used in the Rowland mount at normal diffraction to provide high spectral resolution in the far-ultraviolet region. By assuming that astigmatism and spherical aberration are geometrically corrected by an ellipsoid, we show that holography can be used to correct the remaining prominent second-type coma. Stigmatic sources require a laser wavelength that is too far in the ultraviolet for current recording technology. However, at 3336 A a simple compact symmetric mount, which involves two spherical mirrors, can generate aberrated wave fronts that can be used to record a coma-corrected holographic grating. When compared with the equivalent equally spaced straight-groove grating, which requires a modified ellipsoid substrate, holography cancels the additional asymmetrical term of deformation that permits the use of a simpler surface for the substrate. Some areas of potential difficulty in the holographic mounting are briefly analyzed.