PHOTON-CORRELATION SYSTEM FOR FLUORESCENCE LIFETIME MEASUREMENTS

The construction and testing of a dual-channel photon correlator is re ported for the frequency domain imaging of fluorescence lifetimes usin g photon-counting. detection. A light source modulated at radio freque ncy excites fluorescence, which is detected using an imaging single-ph oton detector. After discrimination, single-photon events are processe d in parallel by the correlation circuit, the purpose of which is to a llow both the mean phase delay and the demodulation of fluorescence to be calculated relative to a reference signal derived from the modulat ed excitation source. Outputs from the correlator are integrated in a computer, resulting in accumulation of images which have been statisti cally filtered by sine and cosine transforms, and which can be manipul ated within the computer to generate a resultant image where;contrast depends on fluorescence lifetime rather than fluorescence intensity. ( C) 1995 American Institute of Physics.