  We performed an experimental study to determine the pixel recovery time of
various Multi Pixel Photon Counters (MPPCs) in order to characterize their rate
capability and double-hit resolution. The recovery time constant and its
dependence on the operating voltage has been evaluated by measuring the
photosensor response to two consecutive laser pulses with varying relative time
differences of a few ns (2-3 ns) up to some 100 ns using a waveform analysis
technique. A Monte Carlo simulation tool is being developed to model the MPPC
recovery process and interpret experimental data. In this context, the
influence of after-pulsing, cross-talk and dark-noise on the recovery process
can be studied.
