Observation of magnetically induced transverse diffusion of light

PHOTONS and electrons, despite their very different nature, show many similarities in their behaviour. Several photonic counterparts of established electronic phenomena-such as photonic energy bands(1), weak localization(2-4), and the quantization of(5) (and fluctuations in(6-8)) optical transmission-have now been observed. These similarities originate in the wave-like character of both photons and electrons, But unlike photons, electrons are also charged, and thus experience the Lorentz force in a magnetic field. This force leads to the well known Hall effect, in which the application of a magnetic field to an electron-transporting medium generates a new current (or voltage) perpendicular to the direction of both the original current and the applied magnetic field. Despite the absence of photonic charge, one of us has predicted(9) that the propagation of light through a disordered, scattering medium should be similarly affected by a magnetic field, although the origin of the effect is very different. Here we report the experimental confirmation of this phenomenon.