Study on Immersion Grating Used in Weak Carbon Dioxide Band Detection Spectrometer

The imaging spectrometer monitoring the CO2 content in the atmosphere is mainly divided into the weak CO2 band and the strong CO2 band. Compared with the strong CO2 band, the weak CO2 band has a relatively clean spectrum, less interference from water vapor and other gases, and weaker CO2 absorption, and the instrument can receive stronger ground-reflected solar radiation signals. However, the concentration of CO2 in the atmosphere is low. To use this band to detect changes in CO2 concentration, it is necessary to ensure that the detection instrument has a sufficiently high spectral resolution. Using the immersion grating as the dispersive element in the spectrometer can greatly reduce the size and weight of the instrument while achieving high spectral resolution. In this paper, the quartz immersion grating used in the weak CO2 detector is optimized and designed, the groove parameters of the grating are designed and optimized according to the requirements of the weak CO2 detector used, and the rectangle and different bottom angles are designed and optimized in consideration of the actual production error. In the 1.595 similar to 1.625 mu m band, the duty cycle of the rectangular groove is 0.3 similar to 0.35, the groove depth is 560 similar to 630 nm, and the TiO2 thickness is 110 similar to 120 nm, the diffraction efficiency of the grating is higher than 80%; the duty ratio is 0.4 similar to 0.45, When the groove depth is 590-660 nm and the TiO2 thickness is 100-105 nm, the diffraction efficiency of the grating is higher than 80%. When the duty ratio of the trapezoidal groove is 0.3 similar to 0.35, the bottom angle of the trapezoid is 82 degrees similar to 86 degrees, the groove depth is 590 similar to 630 nm, and the TiO2 thickness is 120 similar to 125 nm, the diffraction efficiency of the grating is higher than 80%. When the duty ratio of the trapezoidal groove is 0.4 similar to 0.45, the bottom angle of the trapezoid is 82 degrees similar to 86 degrees, the groove depth is 620 similar to 670 nm, and the thickness of TiO2 is 105 nm, the diffraction efficiency of the grating is higher than 80%.