Photocount correlation function

In measurements of thp photocount correlation function an amplifier-discriminator system is placed after the PM. This system rejects small signals corresponding to noise in the circuits and amplifies and standardizes the PM pulses. The pulses are then counted and the photocount correlation function computed. 

It is thus necessary to use the correlation technique. In our horaodyne correlation experiment, we directly obtain C(t)"a(l+b02(t)), in which b is a spatial coherence factor and a depends on the average number of photocounts in the sampling time. The 0(t) correlation function is the Fourier Transform of the central line of Fig. 1. This correlation function will be supposed latter to have a particular form depending on two parameters characterizing the relaxation process. 

The photocount correlation function gPl (t) is given by Eq. (10.30), where t is the correlation delay time. 

Chu et al. have studied the structure and dynamics of a polymer solution composed of PS(polystyrene), PMMA(poly(methyl methacrylate)), TOL(toluene), and CNA(a-chloronaphthalene). According to the photocount intensity-intensity time correlation function measurements of the PMMA probe in the PS/MS(mixed solvent) isorefractive matrix, one surprising feature was that at least two dominant characteristic modes appeared even at small scattering angles. While the slow mode could be identified with the translational motion of the center of mass of the PMMA probe chain, it remained unconfirmed that the fast mode might be related to a coupling of PMMA motion with the cooperative motion of the isorefractive PS/MS(matrix). 

The CONTIN method uses a regularization technique to seek smooth solutions, no matter whether the G(r) distribution is unimodal, multimodal, or broad. So the CONTIN method is appropriate for photocount correlation profile analysis without an a priori assumption on the form of the G(r) distribution. We used the CONTIN method, which was kindly provided by Dr. S.W. Provencher (European Molecular Biology Laboratory), mainly for correlation function profile analysis of unimodal and bimodal G(r) distributions. 

The phase-dependent directionality of photocurrents produced by such a detector entails advantageous properties of the photocurrents cross correlations in nonoverlapping time intervals or spatial regions (considered in Section 4.2.2). These directional time-dependent correlations are measured with one detector only. They involve solely terms dependent on LO phases, in contrast to similar correlations measured by conventional photocounters, which inevitably contain terms depending on photon fluxes such as the LO excess noise. Owing to these properties, the mean autocorrelation function of the SL quadrature is shown in the schemes considered here to be measurable without terms related to the LO noise. LO shot noise, which affects the degree of accuracy to which this autocorrelation is measured (i.e., its variance) is easily obtainable from zero time delay correlations because the LO excess noise is suppressed. The combined measurements of cross correlations and zero time delay correlations yield complete information on the SL in these schemes. 

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