Fluorescence rejection in Raman spectroscopy by a gated single-photon counting method

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Abstract
Raman measurements on ethanol containing rhodamine 6G have been carried out by a single-photon counting technique with highly repetitive (∼82 MHz), short-duration (∼5 ps) laser pulses using a time gate as narrow as 31 ps. The Raman-to-fluorescence intensity ratio and the signal-to-noise ratio have been improved by factors of 129 and 4.2, respectively. These values are in good agreement with numerical estimations. This method has also been found to be very effective in reducing dark counts and interfering plasma lines from the laser tube. The optimum width and position of the gate to attain the best signal-to-noise ratio for a given fluorescence decay time and a response function of the experimental system are also discussed.