Measurement of response characteristics of photodetectors with low divergence angle dependence

A low divergence angle dependent trap photodetector was designed based on two photodiodes and a concave mirror, which can adapt to measurement of both spatially collimated beam and divergent beam in a small space. To determine responsivity of the trap detector, cryogenic radiometer system is used to calibrate trap detector under the condition of collimated beam, while the angular dependence can be ignored at a certain uncertainty level. Responsivity of trap detectors based on silicon photodiodes are calibrated traceable to cryogenic radiometer, with an uncertainty of less than 0.1%. The uniformity of photodetector is measured to be about 0.03% in a 5mm×5mm sensitive area and angular dependence is less than 0.1% when the angle between the incident beam axis and the normal direction of the detector surface is less than 7 degrees. The results show that the detector with this structure has a good consistency in the response of measuring collimated light beam and divergent light beam within a certain divergence angle.