Conical diffraction of a synchrotron beam to probe the efficiency and morphology of blazed gratings

This study explores the use of synchrotron measurements as a nanometrology tool for blazed gratings. In grazing-incidence geometry, one can measure both the conical diffraction and the diffuse scattering on the grating simultaneously in a single scattering pattern. The sensitivity of scattering patterns to the structure of blazed gratings is evaluated. The diffraction component of the pattern is shown to be sensitive to the average groove profile of the gratings, while the diffuse scattering depends on the roughness morphology of the reflective surface of the blazed gratings. These findings are supported by numerical simulations. The simulations were performed using several rigorous solvers for the Helmholtz equations and with perturbation theory. The analysis relies on synchrotron data, as well as on data from atomic force microscopy and scanning electron microscopy. The aim of this article is to draw the attention of the optical community to synchrotron measurements as a nanometrology tool for modern optical elements.