Infrared Absolute Calibrations Down to 10 fW in Low-Temperature Environments at NIST

The Low Background Infrared (LBIR) facility at the National Institute of Standards and Technology (NIST) is responsible for absolute IR radiometric calibrations (SI traceable) in low-background temperature (below 80K) environments. IR radiometric test hardware that needs to be operated in cryogenic environments is calibrated in cryogenic vacuum chambers maintained by the facility to create environments that simulate the low-temperature background of space. Transfer radiometers have also been developed to calibrate IR radiometric test hardware that is too large to ship to NIST from their own IR test facilities. The first generation transfer radiometer, the BXR, is a filter-based radiometer that utilizes an As-doped Si blocked impurity band detector, and can calibrate IR test chambers to a total uncertainty of less than 3% (1 sigma) at irradiance as low as 10(-14) W/cm(2). The BXR has evaluated 9 chambers and the performance of a subset of these chambers will be discussed to a limited extent to demonstrate the need for calibrating IR test chambers. The second generation transfer radiometer, the MDXR, and new primary standards allowing absolute calibrations as low as 10(-15) W/cm(2) are in the final stages of development. The MDXR will have all the functionality of the BXR and it will have a cryogenic Fourier transform spectrometer (FTS) for high resolution spectral capability. Performance specifications and test results from development activity on the new primary standards will be discussed.