A TWO-DIMENSIONAL ATOM GAS (2DAG) has been optically trapped for the first time. Two-dimensional arrays of particles are rare: 2-dimensional electron gases (2DEG) are at the heart of the quantum Hall effect, and planar sprinklings of atoms at the surface of a superfluid have been studied. But only now have physicists been able to trap atoms in a quasi-2-dimensional pancake only 200 nm thick about 800 nm above a gold substrate. Harald Gauck (harald.gauck@uni-konstanz.de, 011-49-7531-88-3837, -3752) and his colleagues at the University of Konstanz use a battery of lasers to cool and confine argon atoms in what is essentially a planar resonant cavity for atom waves. By shaping the local light fields, the researchers hope to fashion planar structures such as miniaturized atom interferometers and even one-dimensional atom waveguides. The planar gas of argon atoms is not dense enough to fall into a Bose-Einstein condensate, but the Konstanz optics setup might lend itself to achieving eventually a 2D condensate. (Gauck et al., Physical Review Letters, 14 December 1998; see figure at Physics News Graphics .)