MULTILAYER GRATINGS EFFICIENCY - NUMERICAL AND PHYSICAL EXPERIMENTS

Recently the possibility of focusing, imaging and spectroscopy with Fr esnel zones etched on a flat multilayer substrate instead of a curved substrate has been shown. This is now known as Bragg-Fresnel Multilaye r lenses (BFML). Lamellar gratings etched in a multilayer (LMG) are th e basic type of Bragg-Fresnel optics. In this paper we describe import ant points in the fabrication, computer simulation, and testing of the LMs. They can be very interesting as a spectroscopic device with a re latively high dispersion and efficiency. We develop a rigorous theory of diffraction combined with the layer-by-layer differential integrati on numerical method. The agreement with experimentals results obtained for a lamellar grating with several period and various etched depths in a W/Si multilayer is very good. The main result is an increase of t he effective extinction depth (t(ext)) in short-period gratings which gives a possibility to increase the absolute diffraction efficiency of the LGM practically from 30% to 60% in the first order with a totally suppressed zero order.