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Design, calibration, and application of a cryogenic low-background infrared radiometer for spectral irradiance and radiance measurements from 4 um to 20 um wavelength

Published

Author(s)

Simon G. Kaplan, Solomon Woods, Eric L. Shirley, Adriaan C. Carter, Timothy M. Jung, James E. Proctor, Dale R. Sears, Jinan Zeng

Abstract

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.
Citation
Optical Engineering
Volume
60
Issue
3

Keywords

radiometer, infrared, cryogenic, calibration

Citation

Kaplan, S. , Woods, S. , Shirley, E. , Carter, A. , Jung, T. , Proctor, J. , Sears, D. and Zeng, J. (2021), 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)
Created March 2, 2021, Updated April 22, 2021