Three dimensional intensity correlation function.

The speckle field generated by a stocastic sample is formed by speckles extending in both the orthogonal and parallel direction with respect to the direction of propagation of the wave. The intensity measured in a plane perpendicular to the direction of propagation varies as the plane is moved; small movements of the plane will give small variations in the intensities. As a matter of facts, the speckles appear and disappear as the plane is moved. This allows us to speack of the three dimensional appearence of the speckles. We will show that the speckles are elongated in the direction of the propagation of the light. If the diamer is $\alpha$ times a wave length $\lambda$, their length is $\alpha^2$ times $\lambda$.

In the following sections, we will show that the three dimensional correlation function of the intensity of the scattered light gives more informations than the two dimensional one; in some cases it is possible to determine the sign of the field correlation function, thus determining it completely. Moreover, in analogy to the quadratic relation between the diameter and length of a speckle, the longitudinal frequencies should be related to the square root of the frequencies of the sample: measuring the longitudinal correlations should double the dynamic of the system.

Hosted by www.Geocities.ws