Number 164 (Story #2), February 10, 1994 by Phillip F. Schewe and Ben Stein OPTICAL LATTICES are three-dimensional ensembles of tens of millions of atoms held together in a crystal-like array not by the customary action of chemical bonds but with light waves from lasers. This pattern of trapped atoms cannot properly be called a crystal because in current experiments only about one in ten possible lattice sites are occupied by an atom. Furthermore, the atoms in optical lattices are hundreds of times further apart than in ordinary crystals. As a result this novel form of matter is a billion times more diffuse than conventional crystals. Nevertheless, there is much more order in an optical lattice than in "optical molasses," in which atoms are confined within an amorphous glob by laser light. To make a true lattice, scientists at labs around the world---at NIST, the University of Munich, and the Ecole Normale Superieure (ENS) in Paris---must first cool the atoms to low temperatures (2.5 microkelvins in the case of the ENS experiment with cesium atoms) so that the relatively weak electric fields of the laser beams can trap the atoms. Optical lattices may be useful in establishing a more precise form of atomic clock, if an atomic-transition signal can be strengthened by increasing the density of atoms in the lattice, or (in a two-dimensional form) as a means of inscribing 10-nm-wide features on integrated circuits. (New Scientist, 29 Jan.)