LBIR Fluid Bath Blackbody for Cryogenic Vacuum Calibrations

We have designed, built and tested a fluid bath blackbody for use as an infrared optical source at the input of a cryogenic vacuum calibration chamber. Stability and uniformity of the blackbody core temperature are maintained by a temperature-controlled circulator and by stirrers in the large fluid bath surrounding the core. The blackbody cavity is coated with specular infrared absorbing paint and has a measured emissivity of approximately 0.9997 at a wavelength of 10.6 micrometers. We will present radiance temperature measurements of the fluid bath blackbody made at contact temperatures from 300 K to 375 K using a primary standard absolute cryogenic radiometer. These experiments are part of an effort at the NIST Low Background Infrared (LBIR) Facility to make a broadband comparison of the power scales defined by a primary standard source and a primary standard detector operating within the same calibration chamber