4 9. I.M. Vellekoop, E.G. van Putten, A. Lagendijk, and A.P. Mosk, “Demixing light paths inside disordered metama- terials,” Opt. Expr. 16, 67–80 (2008). 10. S.H. Simon, A.L. Moustakas, M. Stoytchev, and H. Sa- far, “Communication in a Disordered World,” Physics Today 54, 38–43 (2001) 11. M. Fink, “Time-reversed acoustics,” Phys. Today 50 34– 40 (1997) 12. I.M. Vellekoop, A. Lagendijk, and A.P. Mosk, “Ex- ploiting disorder for perfect focusing,” Nature Photon. (2010), doi:10.1038/nphoton.2010.3 13. O.L. Muskens and A. Lagendijk, “Broadband enhanced backscattering spectroscopy of strongly scattering me- dia,” Opt. Express 16 1222–1231 (2008) 14. M.U. Vera and D.J. Durian, “Angular distribution of diffusely transmitted light,” Phys. Rev. E 53 3215–3224 (1996) 15. J.G. Rivas, D.H. Dau, A. Imhof, R. Sprik, B.P.J. Bret, P.M. Johnson, T.W. Hijmans, and A. Lagendijk, “Ex- perimental determination of the effective refractive in- dex in strongly scattering media,” Optics Commun. 220 17–21 (2003) 16. P. H. van Cittert, “Die wahrscheinliche Schwingungsverteilung in einer von einer Lichtquelle direkt oder mittels einer Linse beleuchteten Ebene,” Physica 1, (1934), as discussed in Ref. [18]. 17. F. Zernike, “The concept of degree of coherence and its application to optical problems,” Physica 5, 785 (1938), as discussed in Ref. [18]. 18. J.W. Goodman, “Statistical optics,” Wiley, New York, (2000). 19. B. Richards and E. Wolf, “Electromagnetic Diffraction in Optical Systems. II. Structure of the Image Field in an Aplanatic System,” Proc. R. Soc. London, Ser. A 253 358–379 (1959)