Measurements and modeling of high groove density multilayer gratings for EUV spectral range in classical and conical mountings

In this work, we study high groove density gratings coated with periodic or aperiodic multilayers, focusing on their extreme ultraviolet performance in both classical and conical diffraction geometries. We first analyze the evolution of the grating profiles during multilayer deposition through transmission electron microscopy imaging and compare the results with previous atomic force microscopy measurements. Using grazing-incidence X-ray reflectometry and synchrotron radiation at oblique incidence, we experimentally characterize the diffraction efficiencies of −1, 0 and +1 orders in classical and conical mountings. Our results reveal asymmetries between +1 and −1 orders and highlight the limitations of usual modeling approaches. Two distinct theoretical models are employed to simulate and interpret the measured data, providing deeper insight into the interplay between grating geometry, multilayer structure, and diffraction behavior. Newly available optical constants for aluminum are also included in the models. These findings contribute to the development of more accurate predictive models which are required for advanced extreme ultraviolet instrumentation, where high efficiency and spectral resolution are critical.