Fast Variable-Temperature Cryogenic Blackbody Sources for Calibration of THz Superconducting Receivers.

Featured Application: Infrared and millimeter-wave band astronomical superconducting receivers require precise sources for instrument monitoring and calibration inside the cryostat. A cryogenic microwave blackbody radiation source with variable radiation temperature is the main tool for calibrating superconducting detectors and mixers. To avoid 1/f noise, the thermal emitter should have fast electrical modulation speed for lock-in detector mode. An electrically heated blackbody radiation source comprising thin metal film on a dielectric substrate and an integrating cavity was designed, fabricated, and experimentally studied at frequencies from 75 to 500 GHz. Analytical and numerical modeling were performed to optimize the emissivity, spectral uniformity, and modulation frequency of the radiation source with the spherical integrating cavity and thin film absorber. The blackbody emissivity (absorptivity) increased from 0.3 to 0.5 for the bare thin film on dielectric substrate, and up to 0.95 when it was placed inside the integrating cavity. The fabricated source mounted at the 0.5 K stage was used to measure the response time of a few microseconds and for sensitivity measurement down to 10⁻¹⁸ W/Hz^1/2 of the superconductor–insulator–normal metal–insulator–superconductor (SINIS) detector at 100 mK. [ABSTRACT FROM AUTHOR]