Scattering by two-component random distributions of spheres

Theory and prototype (at wavelength lambda = 5 mm) partial coherence scattering data for optical applications in diagnostic measurements on two component suspensions or gases are presented. Results are given for equal volume mixtures of two sizes of moving randomly distributed large spheres for all realizable values of the fractional volume w (the fraction of the slab region container filled by scattering material). The relative index of refraction of the spheres was about 1.017, and their diameters were 6.52lambda and 3.33lambda (so that we used about eight times as many small spheres as large ones for each value of w). The spheres were of lightweight Styrofoam, and their motion arose from turbulent air streams (flowing through grids that form the top and bottom of a Styrofoam container), and the data were obtained in real time by processing the instantaneous phase quadrature components of the scattered field with an electronic analog computer. We give results for the forward scattered coherent phase, for the coherent, incoherent, and total intensities, and for the covariant magnitude and phase which (together with the incoherent intensity) provide the variances and covariance of the instantaneous phase quadrature components. We also consider certain reduced data records (from which the major effects of scatterer size and material have been eliminated) to indicate the dependence of the scattering on the fractional volume and to facilitate comparison with earlier data for distributions of identical spheres.