Design and analysis of argon-filled broadband echelle grating spectrometer based on computational fluid dynamics

This paper proposes a scheme for an argon gas-filled broadband echelle grating spectrometer (EGS) that can cover the far ultraviolet (FUV) bands. Using a combination of fluid analysis and spectral analysis, the paper analyzes the impact of the argon-filling on the spectrometer systematically. The optimal structure for fluid uniformity in the spectrometer is confirmed by simulating and optimizing the spectrometer's gas inlet and outlet positions. The simulation results show that the spectrometer is filled with argon after 95 s, and the lateral position of the echelle grating's specular seat and side wall behind the entrance hole are weak links in the system structure. In the steady state, the medium density in the main light path reaches 4.093 kg/m³, and the medium's refractive index becomes 1.000646, which leads to an obvious deflection for light passing through the echelle grating and the prism. Experimental validation shows that the argon-filled broadband EGS can achieve spectral measurement from the FUV to the near-infrared (NIR) bands. After the argon filling is stabilized, the imaging position in prism dispersion direction is shifted by an average of 7.1 pixels, and in grating diffraction direction is shifted by an average of 3.0 pixels, which affects the imaging position of the optical system and the accuracy of the subsequent spectral reduction. In the future, based on the content of this study, a spectral reduction model combined with the refractive index change of the medium will be established to analyze and compensate the errors caused by argon filling, so as to improve the accuracy of the spectrometer.