Number 349 (Story #2), December 3, 1997 by Phillip F. Schewe and Ben Stein|
A PHOTONIC HALL EFFECT AND PHOTONIC MAGNETORESISTANCE, the optical analogs of phenomena usually associated with electrons moving in solids, have been observed in an experiment involving light beams diffusing through powders (Physics World, November 1997). When electrons flowing through a material are subjected to a magnetic field, the electrons will feel a new force (the Lorentz force) and be deflected in a direction perpendicular both to their original direction and to the field. Photons are not charged and so do not feel the Lorentz force directly. But the field can establish a nonuniform index of refraction in a powdery medium consisting of cerium-fluoride particles with a definite handedness. When circularly polarized light enters this medium it gets deflected. This magnetically induced transverse diffusion of light was observed by scientists in Grenoble, France (Nature, 2 May 1996). A year later the same scientists reported that the transmission of light through a powder of europium-fluoride particles was proportional to the strength of an applied magnetic field---in effect the photonic equivalent of magnetoresistance (Sparenberg et al., Physical Review Letters, 28 July 1997).