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内容記述 |
Laminar-type spherical diffraction gratings overcoated carbon-based materials were designed, fabricated, and evaluated for the purpose of enhancing the analytical sensitivity of the flat-field spectrograph in a VUV region of 35?110 eV. As the design benchmark of numerical calculations, diffraction efficiency (DE) and spectral flux (SF) which is defined by the product of the DE and numerical aperture and correlates with analytical sensitivity of the spectrograph were used. To simplify the feasibility study on the overcoating effects, we assumed a laminar-type grating having a grating constant of 1/ 1000 mm and coated with a Au layer of 30.0 nm thickness and an incidence angle of 84.0°. Optimized groove depth and duty ratio were 30.0 nm, and 0.3, respectively. Also, the optimum thicknesses of overcoating layer were 44 nm, 46 nm, 24 nm, and 30 nm for B4C, C, DLC(diamond-like-carbon), and SiC, respectively. Based on these results, we have fabricated a VLS holographic grating overcoated with B4C having a thickness of 47 nm. For the experimental evaluation, the use was made of the light source of Mg-L and Al-L emissions excited by the electron beam generated an electron microscope, objective flat-field spectrograph, and a CCD imaging detector. The experimental results showed that the spectrograph employing new grating overcoated with the B4C layer indicated almost same spectral resolution and 2.9?4.2 times higher analytical sensitivity comparing with those obtained with a previously designed Au-coated grating having a grating constant of 1/1200mm and used at an incidence of 86.0°. |
