INFLUENCE OF REFLECTING BOUNDARIES AND FINITE INTERFACIAL THICKNESS ON THE COHERENT BACKSCATTERING CONE

We investigate the effect of reflecting boundary conditions on the sha pe of the coherent backscattering (CB) cone of light by measuring the CB cone from a suspension of microspheres as a function of the thickne ss of the glass window containing the sample. The reflection from the air-glass interface is observed to narrow the cone, as previously pred icted and observed; however, the finite thickness of the window introd uces a slope discontinuity in the CB cone. The dominant contribution t o the cone for angles less than the kink is from reflected light, whil e the cone at angles higher than the kink arises from light that direc tly leaves the sample. Thus the study of the CB cone as a function of window thickness offers an experimental method of separating the compo nent of the cone due to interfacial reflectivity from the directly bac kscattered component. Monte Carlo simulations of the path length distr ibution of multiply scattered light were performed and compared well w ith both measurement and theories incorporating reflecting interfaces. It was found that under certain circumstances an interface of finite width lowered the CB cone height. Additionally, high quality measureme nts of the CB cone from Mie scatterers revealed an anisotropy in the c one similar to the case of Rayleigh spheres. Finally, the influence of reflecting boundaries on the decay of the temporal autocorrelation fu nction and the height of the CB cone were investigated.