  The frequency correlations of light in complex photonic media are of interest
as a tool for characterizing the dynamical aspects of light diffusion. We
demonstrate here that the frequency correlation shows a pronounced angle
dependence both in transmission and in reflection geometries. Using a broadband
white light supercontinuum, this angle dependence is characterized and
explained theoretically by a combination of propagation effects outside the
medium and coherent backscattering. We report a strong dependence of the
coherent backscattering contribution on the scattering strength which cannot be
explained by the diffusion theory. Our results indicate that coherent
backscattering of the frequency correlation forms a sensitive probe for the
breakdown of the diffusive regime near localization.
