小型掠入射式近边X射线吸收谱仪的设计

近边X射线吸收精细结构(NEXAFS)谱包含了吸收原子的局域结构信息,由于其适用范围广,灵敏度高,已经成为研究物质结构的重要手段之一。为了研究有机物的碳1s NEXAFS谱,本文基于气体激光等离子体X射线光源,采用具有平场特性的凹面变线距光栅作为分光元件,面阵CCD作为光谱探测器,设计了一台小型掠入射式近边X射线吸收谱仪。通过优化光栅和CCD的装配方案,得到了入射角88.6°的装配参数。利用光线追迹法分析了谱仪的分辨率,该谱仪工作波段2~5 nm,在4.4 nm处分辨率可达666。通过分析各结构参量误差对谱线半高宽的影响发现,半高宽对入射角的误差最为敏感,优化的装配方案可以实现入射角的高精度调节。利用氮气等离子体光谱测试了光谱仪的性能,结果显示分辨率达到设计指标。

Design of a compact spectrometer under grazing incidence conditions for near-edge X-ray absorption spectroscopy

Near edge X-ray absorption fine structure(NEXAFS) spectrum contains the local structure information of the absorbing atoms. Due to its wide range of applications and high sensitivity, it has become an important method to study the structure of materials. In order to study the NEXAFS spectrum of carbon in organic substances, a design of a compact spectrometer under grazing incidence conditions is presented, based on a laser-produced plasma source using a gas target. An aberration corrected flat-field grating and a CCD camera are used to detect the spectrum. To achieve the high precision adjustment of the incident angle of the grating, an optimized scheme where the incident angle is 88.6° has been given. Using ray tracing, the resolution of the spectrometer is analyzed. It is about 666 at 4.4 nm in the wavelength range of 2-5 nm. From the influence of each parameter error on the image width, it is found that the error of the incident angle is the most sensitive, and using the optimized assembly scheme is able to achieve the high accuracy adjustment of the incident angle. The performance of the spectrometer has been tested using the nitrogen plasma spectrum, and the results show that the resolution reaches the design index.