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 responsivity scale in the spectral range 0.95 µm to 1.6 µm. The responsivity scale was established by calibrating InGaAs photodiodes against the PTB radiation thermometry cryogenic radiometer (RTCR) using several laser sources: a Ti:sapphire laser (0.850 µm to 1.02 µm); a Nd:YAG laser (1.064 µm); and two diode lasers (1.31 µm, 1.55 µm). At intermediate wavelengths the responsivity was interpolated with the help of thermal cavity detectors of high emissivity. In this way the high accuracy of the scale at the laser wavelengths can be maintained over almost the entire spectral region. A detailed discussion is given of the uncertainties achieved in the calibration with the RTCR and the interpolation with the thermal detector.