MULTIPLEXED SINGLE-PHOTON COUNTING .2. THE STATISTICAL-THEORY OF TIME-CORRELATED MEASUREMENTS

We present the statistical theory governing the operation of multiplex ed time-correlated single-photon counting (MUX-TCSPC) fluorometers whi ch incorporate multiple detection channels and a single time-to-amplit ude converter. The requirement to reject coincident counts in differen t detection channels leads to binomial photon counting statistics. The overall data collection probability is mapped out in terms of the ''s tart'' repetition rate, the number of detection channels, the ''stop-t o-start'' rate ratio per detector, and the dead time. The overall coll ection probability is shown not to be proportional to the number of de tection channels, but to be maximized at similar to 0.37, which still compares very favorably with the equivalent pileup limited probability of similar to 0.01 for a single detection channel. Excellent agreemen t with our theory is demonstrated for experimental data with 2 and 16 detection channels. Potential sources of errors when using MUX-TCSPC t o record fluorescence anisotropy and spectra are described. The theory we describe provides a model for photon counting with multiple detect ion channels which is quite general and also applicable to other field s such as time-resolved imaging using photon migration in tissue and o ptical time-domain reflectometry. (C) 1996 American Institute of Physi cs.