title: Experimental measurements and noise analysis of a cryogenic radiometer.
abstract: A cryogenic radiometer device, intended for use as part of an electrical-substitution radiometer, was measured at low temperature. The device consists of a receiver cavity mechanically and thermally connected to a temperature-controlled stage through a thin-walled polyimide tube which serves as a weak thermal link. With the temperature difference between the receiver and the stage measured in millikelvin and the electrical power measured in picowatts, the measured responsivity was 4700 K/mW and the measured thermal time constant was 14 s at a stage temperature of 1.885 K. Noise analysis in terms of Noise Equivalent Power (NEP) was used to quantify the various fundamental and technical noise contributions, including phonon noise and Johnson-Nyquist noise. The noise analysis clarifies the path toward a cryogenic radiometer with a noise floor limited by fundamental phonon noise, where the magnitude of the phonon NEP is 6.5 fW/√Hz for the measured experimental parameters.
authors.affiliation: National Institute of Standards and Technology (NIST), 100 Bureau Drive, Gaithersburg, Maryland 20899, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Carr
authors.affiliation: National Institute of Standards and Technology (NIST), 100 Bureau Drive, Gaithersburg, Maryland 20899, USA.
authors.forename: S I
authors.initials: SI
authors.lastname: Woods
authors.affiliation: National Institute of Standards and Technology (NIST), 100 Bureau Drive, Gaithersburg, Maryland 20899, USA.
authors.forename: T M
authors.initials: TM
authors.lastname: Jung
authors.affiliation: National Institute of Standards and Technology (NIST), 100 Bureau Drive, Gaithersburg, Maryland 20899, USA.
authors.forename: A C
authors.initials: AC
authors.lastname: Carter
authors.affiliation: National Institute of Standards and Technology (NIST), 100 Bureau Drive, Gaithersburg, Maryland 20899, USA.
authors.forename: R U
authors.initials: RU
authors.lastname: Datla