Correlation techniques for the improvement of signal-to-noise ratio in measurements with stochastic processes

An AC modulation technique is described to convert stochastic signal variations into an amplitude variation and its retrieval through Fourier analysis. It is shown that this AC detection of signals of stochastic processes when processed through auto- and cross-correlation techniques improve the signal-to-noise ratio; the correlation techniques serve a similar purpose of frequency and phase filtering as that of phase-sensitive detection. A few model calculations applied to nuclear spectroscopy measurements such as Angular Correlations, Mossbauer spectroscopy and Pulse Height Analysis reveal considerable improvement in the sensitivity of signal detection. Experimental implementation of the technique is presented in terms of amplitude variations of harmonics representing the derivatives of normal spectra. Improved detection sensitivity to spectral variations is shown to be significant. These correlation techniques are general and can be made applicable to all the fields of particle counting where measurements are amenable to "dual modulation". The proposed AC modulation technique may be applied in diverse fields like pulse height analysis in nuclear spectroscopy, XRD, XRF, RBS, ESCA, positronium resonance, photon counting etc., for enhancing the SIN ratio. (C) 2003 Elsevier Science B.V. All rights reserved.