Subnanosecond time-correlated photon counting spectroscopy with atmospheric pressure nitrogen laser pumped dye lasers

Abstract

Tunable dye lasers pumped by a transversely excited atmospheric pressure nitrogen laser have been constructed and operated at the repetition rate up to 1.2 kHz with spectral resolution of 0.2 nm. The high repetition rate of the nitrogen laser is made possible through the use of a closed-cycle transverse gas flow system. The tunable dye lasers are combined with a time-correlated single photon counting system for the purpose of measuring nanosecond fluorescence decay. The dye laser pulse, which has an intrinsic <400 ps FWHM, is 740 ps when measured by this laser fluorimeter. This value appears to be characteristic of the transit time spread in the photomultiplier tube. The fluorescence decay curve of fluorescein could be measured at a concentration of 3.2×10−11 M with a fluorescence spectral resolution of 0.5 nm. The fluorescence lifetimes of fluorescein and benzo(a)pyrene were determined to be 5.05±0.05 and 44.18±0.05 ns, respectively. Comparisons with cavity-dumped and mode-locked dye laser excitation systems are described, with emphasis on application to spectroscopic studies.