Abstract
A silicon single-photon avalanche diode (SPAD) detector and a proximity-focus-type microchannel-plate photomultiplier tube (MCP-PMT) are compared with respect to their performance in time-correlated single-photon counting (TCSPC) applications. A solution of pinacyanol (1,1′-diethyl–2,2′-carbocyanine) in ethanol, which is used as a test substance with short-lived fluorescence, is excited at 620 nm with a synchronously pumped, cavity-dumped rhodamine 6G dye laser. Deconvolution analysis of the fluorescence decay with a biexponential decay model gives excellent fits to the experimental data recorded with any one of the detectors. The fluorescence lifetimes for the dominating decay component are 13±2 and 11±2 ps as measured at 635 nm with the SPAD detector and the MCP-PMT, respectively. The excellent agreement of these values and the quality of the fits show that the SPAD detector as well as the MCP-PMT can resolve fluorescence decay time constants of the order of 10 ps. This is significantly better than what had been expected on the basis of the instrumental response widths of 70 ps (FWHM) with the SPAD detector and 50 ps (FWHM) with the MCP-PMT.
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