5 - The Coherent Backscattering Effect

Abstract

This chapter provides an introduction to coherent backscattering effect. The coherent backscattering is an interference effect, sometimes also known as the weak localization effect, that manifests itself at the level of configurationally averaged mean intensity. It can therefore directly affect the diffusive behavior when its dynamic ramifications are taken into account. The incoherent background for a thin sample is always decreased by the same factor as the coherent peak, so that the ratio 2 between the coherent peak and the incoherent background is preserved for any sample thickness. Another means of eliminating the long scattering paths is through absorption, which can be characterized by an inelastic scattering length. However, there is a subtle difference between the sample size limitation and the limitation through absorption because absorption is a probabilistic process, whereas sample size limitation is deterministic. Therefore, for a finite sample size L, the paths with lengths shorter than L are not affected. However, if the sample has absorption, there is a finite probability for all paths to be affected, regardless of their lengths.