A single-photon-counting Fourier transform microfluorometer

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Abstract
Describes a microfluorometer, for steady-state and time-resolved analyses, which combines variable-frequency modulation of a continuous light source with single-photon counting electronics. Modulation frequency is easily adjusted to facilitate measurement of a wide range of decay times. Data may be collected at high count rates, whilst maintaining a low probability of photon detection in a single cycle of the modulation. Information equivalent to phaseshift and demodulation ratio is obtained by fast Fourier transform (FFT) of sample and reference data sets. The transform ideally matches the form of data, simultaneously analyses all harmonics present in the modulation and also quantifies the effects of systematic errors.