Establishing a new ultraviolet and near-infrared spectral responsivity scale

A new primary spectral responsivity scale has been established in the ultraviolet (UV) and near-infrared (NIR) spectral regions (200 nm to 400 nm and 0.9 mu m to 2.5 mu m) at an uncertainty level of less than 0.5% (2 sigma) over most of this range. The new scale is maintained on solid-state transfer standard detectors which were calibrated traceable to the NPL cryogenic radiometer via spectrally flat pyroelectric detectors using monochromatic radiation from both laser and monochromator sources. The UV scale was established on GaAsP detectors while the NIR scale is based on InGaAs (0.9 mu m to 1.64 mu m) and modified InSb/sphere detectors (1 mu m to 2.5 mu m). This paper discusses the choice of the new transfer standard detectors, describes how the new scale was established, and analyses the component uncertainties which contribute to the total uncertainty associated with the new scale.