Koike M, Hatano T, Pirozhkov A S, Oue Y, Murano T, Kakio T, Koshiya S, Kondo K, Terauchi M
Kansai Institute for Photon Science (KPSI), National Institutes for Quantum Science and Technology (QST), Kizugawa, Kyoto 619-0215, Japan.
Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, Aoba-ku, Sendai, Miyagi 980-8577, Japan.
Rev Sci Instrum. 2024 Jul 1;95(7). doi: 10.1063/5.0210722.
Multilayer diffraction gratings are designed to improve the detection limit and sensitivity of soft x-ray flat-field spectrographs in the region of 300-1000 eV, placing emphasis on Fe-L (705 eV), Cu-L (930 eV), and Zn-L (1012 eV) emissions. For this purpose, spectral flux was used as the performance index, which is proportional to the amount of optical flux incident into a detector and correlated with detection sensitivity. A super-mirror-type W/B4C multilayer coating [Koike et al., Rev.Sci. Instrum. 94, 045109 (2023)] was employed to improve diffraction efficiency in a wide energy region. The unique feature of the multilayer structure is that the average refractive index and the period length of W/B4C layer pairs are increased from the bottom to top layers. In addition, the incidence angle was reduced to 86.03° from 88.65° and the nominal groove density was increased to 3200 lines/mm from 2400 lines/mm of our previous design, to improve spectral flux while maintaining dispersion and spectral resolution. A holographic varied-line-spacing spherical grating and a soft x-ray flat-field spectrograph were designed, using the aspherical-wavefront-recording method, assuming the nominal grating constant and incident angle described above. The numerical simulation results showed that the spectrograph employing the newly designed grating with the W/B4C multilayer indicated 3.2-8.2 times higher spectral flux compared with those using the previously designed grating while keeping the same spectral resolution.
多层衍射光栅旨在提高软X射线平场光谱仪在300 - 1000电子伏特区域的检测限和灵敏度，重点关注铁-L（705电子伏特）、铜-L（930电子伏特）和锌-L（1012电子伏特）发射。为此，光谱通量被用作性能指标，它与入射到探测器的光通量成正比，并与检测灵敏度相关。采用了一种超镜型W/B4C多层涂层[小池等人，《科学仪器评论》94，045109（2023）]来提高宽能量区域的衍射效率。多层结构的独特之处在于W/B4C层对的平均折射率和周期长度从底层到顶层逐渐增加。此外，入射角从88.65°减小到86.03°，标称刻线密度从我们之前设计的2400线/毫米增加到3200线/毫米，以在保持色散和光谱分辨率的同时提高光谱通量。使用非球面波前记录方法，假设上述标称光栅常数和入射角，设计了一种全息变线间距球面光栅和一台软X射线平场光谱仪。数值模拟结果表明，采用新设计的带有W/B4C多层的光栅的光谱仪，与使用先前设计的光栅的光谱仪相比，在保持相同光谱分辨率的情况下，光谱通量高出3.2 - 8.2倍。
