A Lévy flight for light

Flights of fancy: 'Lévy glass' opens a window on new optical materials Translucent materials such as milk, clouds and biological tissues owe their appearance to the way they interact with light, randomly scattering an incident ray many times before it re-emerges. This process — analogous to the brownian motion of particles in a fluid — is called a random walk, a concept central to statistical physics. It is used, for example, to describe the diffusion of heat, light and sound. An extension of this idea is the Lévy flight, where a moving entity can occasionally take unusually large steps, thereby transforming a system's behaviour. Lévy flights have been recognized in systems as diverse as earthquakes and animal food searches. Barthelemy et al. have now engineered such behaviour into an optical material (titanium dioxide particles in a glass matrix). In the resulting 'Lévy glass', rather than regular diffusion, light waves perform a Lévy flight, in which photons spread around extremely efficiently. This will be an ideal model for studying Lévy flights, and may also lead to novel optical materials. The cover the photons' path, with the light source top right. Photo by Diederik and Leonardo Wiersma