Lifetime Analysis of Weak Emissions and Time-Resolved Spectral Measurements with a Subnanosecond Dye Laser and Gated Analog Detection

Abstract

A relatively inexpensive UV fluorometer has been developed for the temporal and spectral characterization of weak emissions, with the use of a frequency-doubled nitrogen-pumped dye laser for excitation wavelengths down to 260 nm. Gated detection of the photomultiplier pulse provides 0.1-ns resolution of the 1.4-ns FWHM instrument response function. On-line statistical measurements characterize the waveforms, with NATA, tryptophan, and NADH as model compounds providing emission signals of the order of the water Raman scatter signal. Time-decay waveforms are analyzed with the use of nonlinear least-squares fitting, with scatter or p-terphenyl as the reference, and a time shift. Good agreement with the literature is found for the subnanosecond and nanosecond decay times, with resolution of multiple decays down to several percent fractional emission. With multichannel data acquisition, a set of time-windowed emission spectra can be obtained in the same period as is required for an additional time-decay waveform. Time-windowed spectra and the derived decay-associated spectra provide evidence concerning the decay model in addition to spectral characteristics. Practical limitations include the peak current linearity of the photomultiplier and the wavelength variation of the response function.