Construction and tuning of a monophoton decay fluorometer with high- resolution capabilities

A fluorescence decay instrument, assembled largely from commercially available components, is described. This system incorporates a tunable picosecond laser system as an excitation source, energy windowing to minimize artifacts due to pulse pile up and sample alternation to compensate for long-term instrumental drift. The instrument was tested for its ability to resolve multiple exponential decays using methods of moments analysis. By examining the flatness of λ-invariance plots and the accuracy of recovered decay parameters, proper tuning of electronic components and definition of a range of reasonable counting rates was possible. Errors of significance to the resolution of closely spaced decays are discussed. A number of examples are shown for resolutions that are generally regarded as difficult, including two, three, and four components.