Incoherent and chaotic bunching effects

2014 The origin of the chaotic bunching effect is studied from a theoretical point of view. With this in mind, we propose an incohérent atomic source model consisting of atoms excited at stochastically independent times emitting without any interaction. By comparing the fields emitted by such a source and by a chaotic source, we propose the existence of an incoherent bunching effect, the only origin of which is the symmetry of the photons, and less important than the chaotic bunching effect. Moreover, chaotic and incoherent sources are shown not to be identical. LE JOURNAL DE PHYSIQUE TOME 33, NOVEMBRE-DÉCEMBRE 1972, Classification Physics Abstracts 07.00 The problem we are dealing with in this article is the origin of the chaotic bunching effect. The chaotic bunching effect has been first observed by HanburyBrown and Twiss in 1956 [1]. It has been later the object of more precise experiments, on non resonant lines of mercury [2], [3]. The chaotic bunching effect is the following : the second order coincidence probability density (cpd), that is to say, the probability for detecting a photon at a given point and at a given time and another one at another point at a distance a and at the same time, P2B[a], is such that A typical curve of Pc" [a] in terms of all,,,, where 1,,, in the coherence length of the considered field, is given in figure 1. The bunching effect can be interpreted by saying that the detections of two photons in a chaotic electromagnetic field are correlated events. When one photon is detected, the probability for detecting another photon in the same point is twice as large as the probability for detecting another photon at a distance. The origin of this effect is still not clear. In fact, some authors [4], [5] think that it is only due to the symmetry of photons (their property of being bosons) ; some others [6], [7] think that the interactions in the source must be taken into account to explain the observed correlations between the detected photons. Such contradictory explanations come from FIG. l. the fact that these authors consider a free field and don’t analyse the emission process in a definite chaotic source ; thus they cannot relate the bunching effect observed in the emitted field with the properties of the source. The interpretation of the characteristics of a field by the properties of the source has been done for laser sources but not for such usual sources as chaotic sources. In this paper, we would like to clarify our understanding of chaotic bunching effect. As the problem is rather broad and difficult, .we shall focus our attention, for simplicity, on a definite Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphys:019720033011-120102700