and Technology ͑NIST͒ is establishing an infrared detector calibration facility to improve radiometric standards at infrared wavelengths. The absolute response of the cryogenic bolometer that serves as the transfer standard for this facility is being linked to the NIST highaccuracy cryogenic radiometer ͑HACR͒ at a few laser wavelengths. At the 10.6-m CO 2 laser line, this link is being established through a pyroelectric detector that has been calibrated against the HACR. We describe the

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... s, methods, and uncertainties for the calibration of this pyroelectric detector. Apparatus A. High-Accuracy Cryogenic Radiometer As the HACR has been described in detail elsewhere, 5 here we provide only a brief overview of the instrument. A diagram is shown in Fig. 1 . The HACR is an electrical substitution radiometer operated just above the boiling point of liquid helium. An electrical substitution radiometer links a measurement of optical power to the watt by comparing the temper-The authors are with the National