Design, calibration, and application of a cryogenic low-background infrared radiometer for spectral irradiance and radiance measurements from 4 um to 20 um wavelength
Simon G. Kaplan, Solomon Woods, Eric L. Shirley, Adriaan C. Carter, Timothy M. Jung, James E. Proctor, Dale R. Sears, Jinan Zeng
We have constructed, calibrated, and tested a cryogenic low-background infrared radiometer for both spectral radiance and irradiance measurements over the 4 um to 20 um wavelength range. The radiometer has been used to compare two primary methods for measuring the irradiance of highly collimated (< 1 mrad) infrared beams from 10-13 W/um/cm2 to 10-9 W/um/cm2. One method collects the incident radiation using an electrical-substitution absolute cryogenic radiometer, while the other method compares the incident radiation to the collimated output of a blackbody radiator using a cryogenic Fourier-transform spectrometer. Over most of the spectral range we find good agreement between the methods within the combined relative uncertainties of 2.6 % (coverage factor k = 1.) We have also calibrated the radiometer for radiance measurements by using a large cavity fluid bath blackbody that overfills the spatial and angular extent of the radiometer entrance pupil. This source-based radiance calibration is applied to both the discrete filter bands and the spectrometer modes of operation of the radiometer. Measurements are performed in vacuum ( < 10-5 Pa) with an ambient background temperature of 20 K. The radiometric calibration uncertainty analysis of the radiometer as well as its maintenance and stability are discussed.
, Woods, S.
, Shirley, E.
, Carter, A.
, Jung, T.
, Proctor, J.
, Sears, D.
and Zeng, J.
Design, calibration, and application of a cryogenic low-background infrared radiometer for spectral irradiance and radiance measurements from 4 um to 20 um wavelength, Optical Engineering, [online], https://dx.doi.org/10.1117/1.OE .60.3.034102, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=930933
(Accessed April 22, 2021)