基于光线追迹法的低温辐射计光吸收腔设计

Based on the equivalent electrical and optical heating process, radiometers are employed for the metrology of irradiation powers. Working at the liquid helium temperature, the cryogenic radiometer is designed to reduce the nonspontaneous heating by the electric components in the system and is thus currently the most accurate irradiation power metrology measurement facility. During the calibration process of an ideal cryogenic radiometer, the core device-absorption cavity should demonstrate an equivalent temperature increase for the same optical and electrical heating power. However, practical heating routines lack equivalency due to the divergence in the temperature gradient from the complicated optical-matter interactions in black coatings. Herein, utilizing the ray-tracing method, we investigate the tilting angle-dependent spatial optical field distribution in the absorption cavity. With the inclined base angle of the absorption chamber controlled at 60° and the absorption rate of the coating reaching 0.95, the energy of the laser is absorbed in the first and second reflection processes of 98% and 1.9%, respectively, with a ratio of 51.2∶1. The coincidence of the optical and electrical heating paths could thus be realized by placing heaters simultaneously on the inclined bottom plate and the lower side of the absorption cavity. Furthermore, by calculating the time-dependent system temperature with a single inclined bottom heater and calculating the double heater arrangement, an optical-electrical nonequivalency induced by the different heating paths of approximately 0.005% is indicated. Our method constructs an equivalent heating routine for optical and electronic sources, indicating a nonequivalency of 0.005% induced by the different arrangements of heaters. Multiheaters applied with delicate power are recommended to optimize the temperature discrepancy.