A compact extreme ultraviolet high-throughput spectrometer based on the multilayer varied-line-spacing grating

Experimental study and modeling of extreme ultraviolet 4000 lines/mm diffraction gratings coated with periodic and aperiodic Al/Mo/SiC multilayers

Multilayer coated diffraction gratings are crucial components for extreme ultraviolet (EUV) applications such as spectroscopy or spectro-imaging. However, for high groove density, the smoothening of the grating surface profile with multilayer deposition remains a limitation that requires further investigation. In this paper, we report on the design, characterization, and modeling of 4000 lines/mm diffraction gratings coated with periodic and aperiodic Al/Mo/SiC multilayers for EUV radiation. Two types of gratings with different groove depths are compared. Multilayer coatings were designed using a genetic algorithm to maximize the first-order diffraction efficiency in the 17-21 and 19-23 nm wavelength ranges at normal incidence. Periodic and aperiodic multilayers with different numbers of layers were deposited by magnetron sputtering on the two types of fused silica gratings, and the grating groove profile evolution was measured by atomic force microscopy and cross-section transmission electron microscopy. The first-order diffraction efficiency was measured in the EUV at 5° incidence using monochromatic synchrotron radiation and modeled using the rigorous coupled-wave analysis method. The simulation models refined by using the Debye-Waller factor to account for the multilayer interfacial roughness show good agreement with experimental data. The results reported in this study will allow for designing efficient EUV multilayer gratings for high-resolution spectro-imaging instruments.

Reconstruction design method of an aspherical recording optical system for the varied line-space grating

A reconstruction design method for an aspherical recording system for varied line-space gratings is introduced. This method converts the recording system design from achieving specific groove distribution coefficients within the expansion model into reconstruction of the auxiliary mirror surface via the ray-tracing method. The effects of higher-order expansion terms in the expansion model are investigated and more accurate design of the varied line-space grating recording structure is achieved. By varying the surface reconstruction target, this method can be used to design aspherical recording structures with any auxiliary mirror surface shapes.