Cryogenic blackbody calibrations attheNational Institute of Standards and Technology Low Background Infrared Calibration Facility

Abstract

The Low Background Infrared Calibration Facility (LBIR) at the National Institute of Standards and Technology has been in operation for calibration measurements of ihe radiant power emitted fn>rn infrared radiation (IR) sources, such as cryogenic blaclcbodies, for more than 2 years. The IR sources arc sent to NIST by Customers from industiy, government, and university laborato^ii^s. An absolute ciyngenic radiometer is used as the standard detector to measure the total radiant power at its aperture. The low background is provided by a closed cycle helium refrigeration system that maintains the inner parts of Ihe calibration chamber at 20 K. The radiance temper* ature of the blackbody is deduced from the measured power and cottipared with the htackbody temperature sensor data. The calibration procedures and data analysts arc illustrated using the measurements of a typical blackbody.

On the integral law of thermal radiation

“…We believe that the experimental observations in Refs. [17,41] confirm, in the first approximation, the cubic addition to the Stefan-Boltzmann law (9) and the constant law for the difference between the radiant and thermodynamic temperatures (15).…”

“…Geometrical characteristics of these blackbodies are not disclosed due to the confidential nature of these blackbody calibrations [15]. One can still use some experimental data from the radiation measurements that were published in [41] and essentially reprinted in [17]. This is it, we do not need to know an effective size of the tested blackbody in order to derive functions of temperature (9) and (15).…”

“…The contact temperature from one resistance thermometer, T 1 is in the first column of Table 4 of [41]. Geometrical characteristics of the experimental setup (radii of both apertures, distance) from that paper boil down to A = 3.31 · 10 −7 m 2 and B = 2.36 · 10 −3 that enter the formula (1).…”

“…Ref. [41] shows that ∆T , computed with the average of two thermometers temperatures, is linearly proportional in temperature. This fact is further confirmed (without displaying any numerical data though) in the figures and the text of [15].…”

“…If this feature is not an experimental or calibration artifact, then it could only be an effect of higher order terms in the power. Since they were discarded as negligible in [33], quite likely they were neglected in [41] as well. This guess is supported by the fact that the effective size r computed from the temperature difference (15) is twice as big as found above.…”