Absorptance Analysis of Blackbody Cavity in Cryogenic Radiometer
ZHUANG Xin-gang1, 2, LIU Hong-bo1, 2, ZHANG Peng-ju1, 2, SHI Xue-shun1, 2, LIU Chang-ming1, 2, LIU Hong-yuan1, 2, WANG Heng-fei1, 2
1. The 41st Research Institute of China Electronics Technology Group, Qingdao 266555, China
2. National Opto-Electronic Primary Metrology Laboratory, Qingdao 266555, China
Abstract：Cryogenic radiometer is currently the world’s most accurate measurement system in optical radiation power metrology, and the uncertainty of measurement is up to on the order of 10 to the -5th. At present, there are only a few research institutes in the country which have imported cryogenic radiometers from abroad to carry out metrological study. A domestically-made cryogenic radiometer is urgently developed to replace imported products. Because the electrical substitution measurement principle in low-temperature superconducting state is used for optical radiation power measurements, one of the difficulties in the development of cryogenic radiometers lies in the development of a core light radiation receiving device-blackbody absorption cavity. The cavity requires a high spectral absorption over 0.999 9 at each wavelength. For the development of blackbody cavity with high absorption rate, the factors affecting the absorption rate of the blackbody cavity are given systematic analysis in this study. Based on the above, the influences of spectral wavelength, cavity length, diffuse reflectance of dark material, absorption rate of dark material and spatial position of incident light are mainly researched by Monte Carlo ray tracing method. The results showed that the absorption rate of blackbody cavity is positively associated with the absorption rate of dark material. The cavity has a high absorption rate over 0.9999 in the range of 300 nm-1000 nm, and gets the maximum value 0.999 941 5 at 700 nm. Above results indicate that the blackbody cavity meets the design requirements of cryogenic radiometer in the range of 300~1 000 nm. In the later design, the photo-electrical non-equivalent of low-temperature radiometer at different wavelengths should be corrected based on simulation and test results. If the structure and aperture are fixed, the absorption rate of blackbody cavity will gradually increase as the cavity length increases, which changes slowly at 40 mm and gradually tends to balance after 65 mm. Considering the limitation cryogenic radiometer’s cryogenic cabin, it is considered that the best ratio of the cavity length to the aperture is 6.5. The absorption rate of blackbody cavity is also affected by the diffuse reflectance of dark material. With the increase of the diffuse reflection of the black material, the absorption rate of cavity shows an approximately linear decrease. As a result, it is best to choose mirror absorption black material, when the absorption rate is the same. During the change of the absorption rate of black material from 0.8 to 1, the absorption rate of cavity increases by 0.05%. When the black material absorption rate is 0.92, the cavity absorption rate can reach over 0.999 9, which indicates that the black material should have a spectral absorbance over than 0.92 at any point within its effective operating wavelength range. The absorption rate of cavity is also influenced by the spatial position of incident light, which will get higher when the light is closer to the vertex of the inclined bottom cavity. However, the influence of light position on the absorption rate of the cavity is less than 0.004%, which is almost negligible. It is considered that the absorption rate of the inclined bottom cavity is uniform. The research results will have certain reference value for the development of cryogenic radiometer blackbody cavity.
Key words：Cryogenic radiometer; Blackbody cavity; Absorptance; Ray tracing method
庄新港，刘红博，张鹏举，史学舜，刘长明，刘红元，王恒飞. 低温辐射计黑体腔吸收率分析[J]. 光谱学与光谱分析, 2019, 39(07): 2018-2022.
ZHUANG Xin-gang, LIU Hong-bo, ZHANG Peng-ju, SHI Xue-shun, LIU Chang-ming, LIU Hong-yuan, WANG Heng-fei. Absorptance Analysis of Blackbody Cavity in Cryogenic Radiometer. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2019, 39(07): 2018-2022.
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