Number 204 (Story #3), November 23, 1994 by Phillip F. Schewe and Ben Stein A SINGLE-ATOM LASER , a device that produces laser light using one atom at a time, has been created by MIT researchers (K. An et al., 19 Dec. 94 in Physical Review Letters; contact Michael Feld, 617-253-7700). Conventional lasers employ billions upon billions of excited, light-producing atoms or molecules confined in a resonator, a structure that provides the required geometry for laser action. The MIT researchers designed a resonator consisting of two ultra- highly reflecting parallel mirrors spaced 1 mm apart. They then passed a beam of barium-138 atoms between the mirrors in such a way that one atom or less was inside the resonator at any one time. The mirror spacing was fixed to within 10 picometers to maintain proper alignment, and highly efficient detectors recorded the 791-nm-wavelength laser light produced by the barium atoms. The use of a single atom eliminates the effect of inter-atomic interactions; therefore this laser device will be useful for performing precision studies of the interaction between atoms and electromagnetic fields. Moreover, because so few atoms contribute to the electromagnetic field in the resonator, some of the statistically averaged properties that apply to light emitted by conventional lasers do not apply to the so called "non-classical light" emitted in the single-atom laser. (MIT Press Release, 17 November.)