Abstract

The study of periodic signals is of great interest in many fields in physics: spectroscopy, optical communications, laser Doppler velocimetry, etc. The aim of the present work is to show a method that allows us to characterize this type of signal when the light intensity level is low (1–10 photoelectrons per period). In these situations, conventional techniques, such as multichannel analysis and measurement of the second normalized factorial moment, n⁽²⁾(T), would require a long measurement time to obtain the characteristic parameters with a satisfactory accuracy. The proposed method is based on the measurement of the moment generating function of the number of photopulses, Q_n(s,T). For the sake of simplicity and in order to check the goodness of the method, a square wave modulated light beam of period P and modulation factor 2A was chosen. The behavior of the experimental errors in the determination of P and A was studied by means of a theoretical error model. Then, a set of experimental measurements was carried out for different situations. From the obtained results we can conclude that the Q_n(s,T) measurement has two advantages compared with n⁽²⁾(T): the signal-to-noise ratio is greater, and the characteristic parameters of the signal can be obtained with less error in the same experimental conditions. These advantages are particularly enhanced when the fluctuating part of the signal is small and the light intensity is low.

© 1992 Optical Society of America