Slowing and Storing Light in a Solid

When light encounters a medium in which the index of refraction changes dramatically with wavelength, the group velocity of light, the speed at which the wave pulse propagates, can be considerably lowered, even to zero. The energy and information in the original light beam can be stored, without any heating, in the form of a wave of excitations in the spins of the atoms in the medium. Earlier this year two different experiments at Harvard stopped and stored light in a vapor sample (Update 521).

Now the feat has been carried out in a solid material in an experiment carried out at MIT and at the Air Force Research Laboratory in Hanscom, Massachusetts. This is a nice advance since in general information processing is carried out in solid-state integrated devices. The medium used, a yttrium-silicate crystal doped with atoms of the rare earth praseodymium, is already commonly used as a medium for high-density optical data storage.

The researchers (contact Philip Hemmer, 781-377-5170, philip.hemmer@hanscom.af.mil) foresee many applications for slow or stopped light in a solid, in areas such as quantum computing, ultra-sensitive magnetometry, and acousto-optics (if light is slowed to subsonic speeds, strong coupling between light and sound waves becomes possible). (Turukhin et al., Physical Review Letters, 14 January 2001.)