First demonstrated in the early 1990s, electromagnetically induced transparency (EIT) takes advantage of the quantum properties of an opaque atomic gas to allow photons to pass through without absorption. Researchers subsequently proposed that a classical analog to the quantum effect, called magnetically induced transparency, could occur in a plasma. In a paper in Physical Review Letters, Raanan Gad at Technion - Israel Institute of Technology in Haifa and colleagues report their experimental observation of this phenomenon.
Normally a plasma blocks electromagnetic waves of certain frequencies. However, if magnetic fields of the right structure and intensity are applied, the plasma acquires a band structure in which certain propagating electromagnetic waves no longer couple to the electrons and instead pass through without being absorbed. Gad et al. tested this prediction by launching a microwave pulse through a plasma surrounded by coils to produce the required magnetic fields. By comparing the pulse transmission with and without one of the magnetic fields, Gad et al. were able to measure the magnetically induced transparency. Not only does this suggest ways for controlling plasma properties, but the work may also provide a method for creating, in plasmas, the trapped and slow light effects that are based on the original EIT work. – David Voss