Measurement of Low Light Intensities by Synchronous Single Photon Counting

Abstract

Single photon counting technique is used for measuring continuous light fluxes of very low intensity suitably modulated. Demodulation and integration processes usually made in conventional synchronous detectors on analog signals are here performed with drift free digital operations. The main advantage of this procedure is the possibility of improving the signal-to-noise ratio by very long integration times which are not limited by drifts of the electronics following the detector. An analysis of the noise filtering properties of the device is given. Raman light angular distributions obtained by this technique are reported as an example and noise characteristics of the device are measured and compared with the results of the theoretical analysis.