Design of soft X-ray high diffraction efficiency diffraction gratings with hybrid multilayer coatings in an energy range of 200‒900 eV

There has been a growing interest in state analysis near the Fe-L emission (705 eV, 1.76 nm) for the various purposes including a reduction of the weight of steel of automobile steel sheets while keeping sufficient strength. This paper presents on a theoretical study to explore the substantial enhancement of diffraction efficiency and spectral flux of laminar-type diffraction gratings around Fe-L emission spectrum. This spectral region is known as difficult to obtain a significant increase of diffraction efficiency merely employing a conventional X-ray multilayer coating due to short penetration length for low energy X-ray under grazing incidence condition. To overcome this difficulty, we conceived a hybrid layer structure which is consisting of a soft X-ray multilayer of a few pairs of bilayers having high reflectivity and small extinction coefficient on a conventional metal layer. The assumed parameters of the grating are as follows: laminar type with groove density of 2400 lines/mm; groove depth of 6.2 nm; duty ratio (land width/groove period) of 0.4; metal layer of Au having a thickness of 30 nm; multilayer; one, two, and three pair(s) of a C and W layers. The assumed thickness of C and W layers are 7.4 nm and 6.0 nm, respectively, and the incident angle is assumed to be 86.20 °. The calculated diffraction efficiency of the grating with two or three pairs of C and W layers on Au layer exceeds 0.10 at the vicinity of 705 eV and shows a practical efficiency of 0.03 or more in a wide spectral range of 200 eV to 900eV. For the case of an objective spectrograph the above decrease of the incident angle implies over two times increase of the incident flux on the grating compared with a spectrograph employing a conventional grating. Finally, considering with the enhancement of diffraction efficiency, an objective spectrograph installed a new grating can gives over five times increase of spectral flux on the image plane.The 40th International Conference on Vacuum Ultraviolet and X-ray Physic