Semiconductor powder provides for Anderson localization of light

Semiconductor powders with a high refractive index—about 3.48—have allowed researchers at the European Laboratory for Non-Linear Spectroscopy (Florence, Italy) and the Van der Waals-Zeeman Laboratory (Amsterdam, The Netherlands) to experimentally demonstrate Anderson localization of light. The phenomenon is a disorder-induced phase transition, observed, for example, in the electron-transport behavior change from the classical regime where Ohm`s law prevails to a localized state in which the material behaves as an insulator. The origin of the effect is electron interference due to multiple elastic scattering from defects in the solid form of the material. The researchers used ultrapure ground gallium arsenide crystals, with mean free paths for scattering as low as 0.17 µm. With 1064-nm light, measurement of the transmission coefficient T showed a quadratic dependence on sample length L (T µ L-2), in contrast to a linear dependence for the classical regime. Further decrease of powder particle size changed the quadratic behavior into exponential decay, as expected in the localized regime, where the transport of light has come to a halt. The result may lead to applications in optical data processing, spectroscopy, and laser physics.