New anti-laser absorbs, rather than emits, light beam

In a fascinating case of physics being turned on its head, a group of researchers at Yale University in the US has created an "antilaser" that almost perfectly absorbs incoming beams of coherent light.

Gregory Salamo

Q. Long, Shuyu Zhou, S.Y. Zhon +1 more

The quadrupole magnetostatic field (QMF), together with 3 pairs of laser beams, known as the magneto-optical trap, has been widely used for cooling and trapping atoms. This report concerns itself with some new phenomena observed in fluorescence emitted by Rb atoms in QMF under the circumstances of a single /spl sigma/ laser beam. A circularly polarized laser traveling-wave tuned to D/sub 2/-line is passed through a vacuum chamber along the central axis of two anti-Helmholtz coils. The fluorescence emitted by Rb atoms excited by the circularly polarized light in the direction at right angle to the direction of the incident laser beam is collected and imaged with all polarized directions taken into account. From the camera picture we can see that, around the zero-field point, there exists a dark region, the size of which is inversely proportional to the field gradient and is not sensitive to the detuning. The dark region corresponds to a dip in the profile of the fluorescence intensity versus the space. An attempt is made to explain the origin of this dark region.

Heather M. Hill

Alexander Kubanek, Alexei Ourjoumtsev, I. Schuster +4 more

Single atoms absorb and emit light from a resonant laser beam photon by photon. We show that a single atom strongly coupled to an optical cavity can absorb and emit resonant photons in pairs. The effect is observed in a photon correlation experiment on the light transmitted through the cavity. We find that the atom-cavity system transforms a random stream of input photons into a correlated stream of output photons, thereby acting as a two-photon gateway. The phenomenon has its origin in the quantum anharmonicity of the energy structure of the atom-cavity system. Future applications could include the controlled interaction of two photons by means of one atom.