Near-Field Effects in Mesoscopic Light Transport

In dense multiple scattering media, optical fields evolve through both homogeneous and evanescent waves. New regimes of light transport emerge because of the near-field coupling between individual scattering centers at mesoscopic scales. We present a novel propagation model that is developed in terms of measurable far- and near-field scattering cross sections. Our quantitative description explains the increase of total transmission in dense scattering media and its accuracy is established through both full-scale numerical calculations and enhanced backscattering experiments.

Figure 1

(a)–(c) Intensity distributions in the cross-sectional areas of 3D slabs with reducing lengths as indicated. The media contain $a=100\mathrm{nm}$ radius $\mathrm{Ti}{\mathrm{O}}_2$ particles randomly dispersed throughout the volume. Rings colored in gray denote particles located in the considered cross section, while the white and blue ones indicate particles situated at 100 nm above and, respectively, below that plane. (d) Total transmission as a function of inverse thickness. The blue and black symbols designate the ISA and the results of $T$-matrix calculations, respectively. The inset illustrates the appearance of additional transmission channels due to near-field coupling (see text).

Figure 2

(a) Enhanced backscattering setup. Abbreviations are as follows: $E$, beam expander; $P$, polarizers; BS, beam splitter; BD, beam dumper; QW, quarter-wave plate; $C$, Fourier lens; $S$, sample. (b) Measured transport mean free path compared with predictions of different transport models.