Direct measurement of fluorescence lifetime using high speed data acquisition

Abstract: Time-correlated single photon counting (TCSPC) is commonly used to measure the lifetime of fluorescence from dye molecules. In TCSPC, the sample is excited by a pulsed laser and the arrival time of each of the emitted photons at the detector relative to a trigger is recorded. An important criterion of the technique is that the excitation intensity of the laser has to be low enough such that the detector detects at most one photon per ten laser pulse excitations. As one needs to detect about 10$^4$ to 10$^6$ photons in order to generate a time trace of the fluorescence, the measurement has to be repeated about 10$^7$ times, which makes the technique rather slow. A typical measurement takes about 1s which is very long when the fluorescence lifetimes of most of the dye molecules range from few nanoseconds to microseconds. In this master's thesis, a novel method based on interleaved sampling and waveform averaging to directly measure the fluorescence decay from the dye molecule Rhodamine 6G is presented. A new algorithm using boot-strapped waveform averaging to improve the effective sampling rate as well as the signal to noise ratio of the digitized signal have been implemented and tested. The new algorithm has enabled us to reduce the measurement time to a few tens of a microseconds, which is approximately a million times faster than the TCSPC method.