Improved calibration of the spectral responsivity of interference filter radiometers in the visible and near infrared spectral range at PTB

At the Physikalisch-Technische Bundesanstalt (PTB) silicon diode-based narrow-band interference filter radiometers (FR) are used for the radiometric determination of thermodynamic temperatures. To extend the temperature range down to 400 °C, the centre wavelength of the FRs was shifted from the visible to the near infrared (900 nm, 1000 nm and 1595 nm). An improved calibration procedure is presented which achieves relative uncertainties for the spectral responsivity of the FRs of the order of 10−4, by taking into consideration the increased temperature coefficient of the spectral responsivity and the nonlinearity of the silicon detectors when operated in the near infrared wavelength region.