A PHASE QUADRATURE CORRELATOR FOR THE MEASUREMENT OF FLUORESCENCE-DECAY TIMES BY SINGLE-PHOTON COUNTING

A novel, low-cost method is reported for the measurement of fluorescence kinetics in microscopic samples using single-photon counting. Detected photons are correlated in-phase and in-quadrature with an excitation source modulated at almost-equal-to 30 MHz. The correlator has a linear phase response, uses a simple ratio counter as output and can reject harmonics in the modulated emission. The system has particular application to the generation of fluorescence images with decay-time-related contrast.