Infrared spectral responsivity scale realization and validations.

An InSb working standard radiometer, first calibrated at the National Institute of Standards and Technology (NIST) in 1999 against a cryogenic bolometer, was recently calibrated against a newly developed low-noise-equivalent-power pyroelectric transfer standard detector. The pyroelectric transfer standard, which can operate at the output of a monochromator, holds the newly realized NIST spectral power responsivity scale between 1.7 and 14 μm with an uncertainty of 1% (k=2). The InSb working standard was also measured at the National Physical Laboratory (NPL) of the United Kingdom in 1999. The less than 2% spectral power responsivity disagreements obtained on the InSb working standard (both from the 1999 NIST and NPL comparison and also against the pyroelectric standard) validate the three independently realized power responsivity scales and verify the long-term stability of the InSb working standard. The InSb working standard was also used in irradiance measurement mode to validate the previously determined spectral irradiance responsivity of four narrowband InSb radiometers that were applied to calibrate IR target simulators. The uncertainty of the present spectral irradiance responsivity scale held by the InSb working standard is 2.5% (k=2) in the 2 to 5.2 μm wavelength range.