Nonlinearity of the quantum efficiency of Si reflection trap detectors at 633 nm

Trap detectors are useful transfer standards well-suited to modern absolute radiometry. A potential problem with them is that cryogenic radiometers allow only small-diameter laser beams to enter the absorber cavity. This can significantly increase nonlinearity effects of the trap detectors even at radiant power levels below 1 mW. The results of nonlinearity investigations at 633 nm of Si reflection trap detectors are presented. Four types of trap were studied: the commercially available QED100 and QED200, and constructed traps using Hamamatsu S1227-1010BN and S1337-1010BN photodiodes. The quantum efficiency was investigated as a function of radiant power as well as of the bias voltage and beam diameter.