THE USE OF DIFFRACTION EFFICIENCY THEORY IN THE DESIGN OF SOFT-X-RAY MONOCHROMATORS

In general, the diffraction efficiency of gratings is limited by the constraints imposed by the type of geometry used to scan the photon energy. In the simplest example, the spherical grating monochromator, the deviation angle, the grating groove width and depth and the groove density are all constrained by considerations of the maximum photon energy and the tuning range for individual gratings. We have examined the case in which these parameters are unconstrained, resulting in predictions of the ultimate performance of lamellar type gratings for groove densities from 300 to 2400 I/mm for gold and nickel coatings. The differential method of Neviere et al. (Nouv. Rev. Opt. 5 (1974) 65) was used for modeling the behavior of the gratings and justification is presented for this by rigorous comparison with measurements. The implications of these results for future monochromators based on a variable-included-angle geometry are discussed.