Angle dependence of the frequency correlation in random photonic media: Diffusive regime and its breakdown near localization

Abstract

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 that 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.

Weak localization of photon noise

“…More specifically, our approach indicates that the enhancement displayed by the noise cone reveals information about mesoscopic correlations. These correlations give rise to deviations from Rayleigh statistics in the strongly scattering regime [44]. The use of the CBS technique has in addition the potential to study the first and second moment of the probability distribution as function of the path length.…”

Frequency correlations in reflection from random media

“…In Sec. IV, we apply this relation to treat frequency correlations between field intensities in the regime of weak disorder, providing a theoretical interpretation for previous experimental results [14] in this regime. Finally, in Sec.…”

“…This fact manifests itself in the effect of coherent backscattering [9][10][11][12][13], leading to a sharp angular cone of the backscattered intensity around the direction ϑ = 0 corresponding to exact backscattering. Consequently, this dependency of the path length distribution on the backscattering angle leads to a characteristic angular peak of the width of the frequency correlation function [14]. In a previous work on reflection from two-and three-dimensional * Corresponding author: thomas.wellens@physik.uni-freiburg.de random wave guides [15], the narrow angular peak that results in the diffusive regime of weak disorder could not be resolved, due to the discrete scattering channel geometry.…”

Speckle correlation functions applied to surface plasmons

“…Calculations can be performed with this expression, but the decorrelation from e i[ k || (λ 0 ) x i − k || (λ 1 ) x i ] may have a strong influence on the correlation function. 16 Hence, we take k || (λ 0 ) = k || (λ 1 ), such that the exponent becomes 1 for x i = x i . The phase of this term is random when x i = x i and k || is sufficiently large, i.e., if we are outside the zeroth diffraction order.…”

“…As it is unclear whether the losses are dominated by absorption or scattering, we study a set of samples with different hole densities. We analyzed a set of nine samples for which the hole density is 1/(qa 2 0 ), where a 0 = 450 nm and q = 1,2, 3,4,9,16,25,36,81. Each sample covers a square area of 400 μm × 400 μm.…”