Abstract: In response to the development needs of high-sensitivity cryogenic radiometer,a cryogenic radiometer absorption cavity is proposed.In this paper,The multiple reflection structure of the ellipsoid diaphragm is designed,and the diffusion welding process is adopted at the same time.The three-part welding formation of ellipsoid diaphragm,oblique opening-oblique bottom cylindrical cavity and oblique bottom surface is realized.In this way,an effective optical trap is formed,so that the radiation incident into the absorption cavity is almost completely absorbed.Preparation of carbon nanotube coatings with porous structure,and the uniform distribution of the coating on the inner wall of the cavity is achieved by spraying-based processes.An absorptivity measurement device was built based on the integrating sphere method,and the absorption rate of the cavity was measured.The results show that the absorption rate is better than 0.999 7 at typical laser wavelengths such as 476.2 nm,488.0 nm,514.5 nm,632.8 nm and 647.1 nm.

Key words: Cryogenic radiometer, Metrology, Diaphragm, Absorption cavity