Precise scale of spectral responsivity for InGaAs detectors based on a cryogenic radiometer and several laser sources

The Physikalisch-Technische Bundesanstalt (PTB) has developed a spectral re sponsivity scale in the spectral range 0.95 mum to 1.6 mum The responsivity scale was established by calibrating InGaAs photodiodes against the PTB ra diation thermometry cryogenic radiometer (RTCR) using several laser sources : a Ti:sapphire laser (0.850 mum to 1.02 mum); a Nd:YAG laser (1.064 mum); and two diode lasers (1.31 mum, 1.55 mum) At intermediate wavelengths the r esponsivity was interpolated with the help of thermal cavity detectors of h igh emissivity. In this way the high accuracy of the scale at the laser wav elengths can be maintained over almost the entire spectral region. A detail ed discussion is given of the uncertainties achieved in the calibration wit h the RTCR and the interpolation with the thermal detector.