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.