On the effects of the time gate position and width on the signal-to-noise ratio for detection of Raman spectrum in a time-gated CMOS single-photon avalanche diode based sensor

Abstract

The effects of the position and width of the time gate on the available signal-to-noise ratio in a time-gated Raman spectrometer are analyzed and measured. The Raman spectrometer used is based on a high power, 532 nm, pulsed laser (500 ps FWHM) and a time-resolving circuit with a single photon avalanche diode (SPAD) detector which is moved by a microstep motor to derive the whole Raman spectrum. The times of arrival of the scattered photons are recorded and the effectiveness of different time gate positions and widths are analyzed by post-processing the measured and simulated data. It is shown from measurements performed on olive and sesame seed oil samples having fluorescence lifetimes of 2.5 ns and 2 ns and Raman-to-fluorescence photon ratios of 0.03 and 0.003, respectively, that the fluorescence background can be substantially suppressed if the width and position of the time gate are properly selected.