A fluctuating fractal nanoworld

The localization of elementary excitations in complex media is one of the most universal and important problems of physics, spanning the range from electrons in disordered materials to acoustic waves in nonuniform media, to light waves in the presence of random scatterers. One of the most fundamental effects in this wide class of phenomena is Anderson localization [1]. This effect is predicted for both classical waves and quantummechanical states in random scattering media and is deeply rooted in general properties of time reversal, which dictate that back-scattered waves add coherently to the original wave packet, leading to its localization. For electrons, the properties of this localization are influenced by, and can be obscured by, electron-electron interactions. In contrast, in linear optics, the propagation and scattering phenomena involve noninteracting photons (or electromagnetic waves in the classical picture). In this case, the scattering can lead to Anderson localization in its purest forms. One of the practical implications of the light localization in strongly scattering media is, for instance, random lasers [2]. Now, as reported in Physical Review Letters, Valentina Krachmalnicoff, Etienne Castanié, Yannick De Wilde, and Rémi Carminati of the Institut Langevin in Paris [3] have, for the first time, experimentally observed the near-field localization and fluctuations of optical energy on a multitude of length scales in disordered nanoplasmonic metal systems.