Soft x-ray high diffraction efficiency and spectral flux laminar-type W/B₄C multilayer diffraction grating for 300–1000 eV.

This article focuses on the design and performance evaluation of a varied-line-spacing (VLS) laminar-type spherical diffraction grating coated with a super-mirror-type (SMT) tungsten/boron carbide (W/B4C) multilayer to enhance the diffraction efficiency and spectral flux of soft x-ray flat-field spectrographs in the 300–1000 eV energy range. The new grating design (G2) features an increased groove density (3200 lines/mm) and a reduced incidence angle (86.03°) compared to a previous gold-coated grating (G1) optimized for 300–2200 eV. Numerical simulations indicate that the G2 grating with the W/B4C multilayer achieves 3.2 to 8.2 times higher spectral flux than the Au-coated G1 while maintaining comparable spectral resolution, primarily due to increased collection solid angle and enhanced diffraction efficiency. The multilayer coating also suppresses unwanted diffraction orders and stray light without significant absorption edge effects, making it suitable for sensitive soft x-ray emission spectroscopy applications targeting emissions such as Fe-L, Cu-L, and Zn-L.