Sub-picowatt precision radiometry using superconducting transition edge sensor bolometers

We describe a cryogenic radiometric calibration system suitable for high sensitivity, low background power bolometers. The system uses a variable temperature blackbody source capable of temperatures of 4 to 20 K, whose output covers the sub-millimeter wavelength regime. The detector is an eight-channel, filled-focal-plane array of superconducting transition edge sensor (TES) bolometers. The system is designed to test components of the optical system such as polarizers, filters and stray light suppressors as well as the performance of the detector array elements. The bolometer response to incident submillimeter radiation is measured and compared to the calculated output of the source seen by the bolometer.