, 183901 (2010) – Published October 25, 2010The localization of elementary excitations in complexmedia is one of the most universal and important prob-lems of physics, spanning the range from electrons indisordered materials to acoustic waves in nonuniformmedia, to light waves in the presence of random scat-terers. One of the most fundamental effects in this wideclass of phenomena is Anderson localization [1]. This ef-fect is predicted for both classical waves and quantum-mechanical states in random scattering media and isdeeply rooted in general properties of time reversal,which dictate that back-scattered waves add coherentlyto the original wave packet, leading to its localization.For electrons, the properties of this localization are in-fluenced by, and can be obscured by, electron-electroninteractions. In contrast, in linear optics, the propaga-tion and scattering phenomena involve noninteractingphotons (or electromagnetic waves in the classical pic-ture). In this case, the scattering can lead to Andersonlocalization in its purest forms. One of the practical im-plications of the light localization in strongly scatteringmedia is, for instance, random lasers [2]. Now, as re-ported in Physical Review Letters, Valentina Krachmal-nicoff, Etienne Castanie, Yannick De Wilde, and RemiCarminati of the Institut Langevin in Paris [3] have, forthe first time, experimentally observed the near-field lo-calization and fluctuations of optical energy on a multi-tude of length scales in disordered nanoplasmonic metalsystems.In general, electromagnetic waves in a dielectric can-not be localized to less than half their wavelength inthat medium because this is the distance needed to ex-change energy between the electric and magnetic com-ponents of the electromagnetic field. However, in plas-monic metal systems this limitation is completely re-laxed because the optical energy is carried by surfaceplasmons, which, in contrast to quanta of electromag-netic waves (photons), are electromechanical oscilla-tions and are not restricted by a characteristic wave-length. Therefore, the optical energy can be localizedat a minimum scale, limited only by the finest inhomo-geneities of the metal down to a few nanometers, whereLandau damping in the metal’s electron plasma sets thelowest scale,