BRAGG SCATTERING FROM ATOMS IN OPTICAL LATTICES

We observe coherently enhanced reflection (Bragg scattering) of a near resonant laser beam from cesium atoms ordered by a periodic array of optical potential wells known as an optical lattice. The reflected lig ht is enhanced by a factor of similar to 10(5) over scattering from a disordered atomic sample. We measure the magnitude of the reflectivity and its detuning dependence as functions of the density and the degre e of localization of the atoms. The change in lattice constant due to the frequency-dependent effective index of refraction seen by the latt ice light field is observed.