On-blaze scanning monochromator for the vacuum ultraviolet.
The Rowland circle mounting for scanning VUV monochromators with concave blazed diffraction gratings can be adapted so that the operation is always on-blaze; that is, the monochromator always operates at maximum efficiency. In principle, this adaptation works at any angle of incidence, but in practice only grazing incidence monochromators are practical. The scanning range of such a monochromator is less than for a conventional monochromator but can be extended by storing gratings with different groove densities on a carousel and rotating them into position as necessary.