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

Metrological Instrumentation

A new setup for a detector-based traceability chain for spectral irradiance measurements, independent from the high-temperature blackbody radiator and synchrotron radiation, 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, a calibrated silicon trap detector, traceable to the primary cryogenic radiometer of PTB, in combination with a well defined aperture is used to determine the spectral irradiance of a uniform monochromatic irradiance field produced by a tunable laser system. With this known uniform irradiance field a spectroradiometer, used as a wavelength tunable-filter radiometer, is calibrated with respect to its absolute spectral irradiance responsivity. The calibrated spectroradiometer finally transfers the absolute spectral irradiance value to other standard light sources. At present, irradiance calibrations of lamps in the spectral range between 565 nm and 975 nm were measured with expanded uncertainties lower than 1% (k=2). This exclusively detector based traceability chain for the spectral irradiance calibrations has the potential to reduce the measurement uncertainty compared to the traditional methods, where sources like blackbody radiators and standard lamps are used as intermediate standards. 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.

TU Braunschweig