Avalanche photodiode based photon counter echo photon number resolving

The solid state photodetectors based on silicon avalanche photodiodes operated in Geiger mode are used for detection of echo signal in laser ranging experiments. The avalanche process nonlinearity enhance the influence of starting conditions to avalanche grow of photodiode output signal. This is the reason why the internal delay of this type of detectors is depended on detected signal intensity. i.e. in case of weak signal it is depended on number of detected photons. The dependence is in the range of 0-200 ps for photon numbers 1-1000 photons. The active quenching and gating circuit with time walk compensation has been constructed to eliminate this effect (Kirchner, 1998). In our experiment. we have used the outputs of the compensation circuit to estimate the photon numbers detected on a shot by shot basis simultaneously with original required time interval estimation. The mutual time difference between the compensated and uncompensated output pulses corresponds to the photon number. Monitoring this time difference by the picosecond event timing device enabled us to monitor the echo signal strength fluctuation on a shot by shot basis in a laser ranging. The experimental results will be presented.