Computation of intensity and polarization state of diffracted fields from reflective gratings in conical geometry

Conical diffraction geometry has interesting properties for monochromatization of short pulse sources of extreme-UV or soft X-ray radiation, like high harmonic generation in gases. It enables high diffraction efficiency at the cost of a reduced angular dispersion. Computation of grating efficiency is complex when the incidence plane is not perpendicular to the grating lines because S and P polarizations are coupled. We have therefore developed a special code, named COROX, which implements a rigorous coupled-wave analysis algorithm. The code is able to compute the complex diffracted field from any incidence direction and polarization on any kind of grating (thick lamellar and blazed gratings with single or multilayer coating). COROX is developed with C++ and uses an eigen linear algebra library. This paper outlines the method of computation, and the results are given for a 150 l/mm blazed grating in a conical Littrow configuration.