Detector-Based Traceability Chain for Spectral Irradiance using Tunable Laser-Based Facility at PTB

A completely detector-based traceability chain for spectral irradiance measurements, independent from the high-temperature blackbody radiator, has been developed at the Physikalisch-Technische Bundesanstalt (PTB). Thus a SI traceability of the spectral irradiance is obtained without any use of calculable radiant sources. At the Tunable Laser In Photometry (TULIP) setup of PTB, The absolute irradiance responsivity of a continuously scannable spectroradiometer is derived from the spectral responsivity of a silicon trap detector, traceable to the primary cryogenic radiometer of PTB. This spectroradiometer can subsequently be used to calibrate the spectral irradiance of photometric and radiometric sources. With this calibration chain the two commonly used calibration steps to measure the blackbody temperature using calibrated filter-radiometers are replaced by the single calibration of the responsivity of the spectroradiometer against a trap detector. At present, irradiance measurements of lamps in the spectral range between 565 nm and 975 nm were measured with expanded uncertainties lower than 1 %.