Lu Deng, Edward W. Hagley, J Wen, M Trippenbach, Y B. Band, Paul S. Julienne, J E. Simsarian, Kristian Helmerson, S L. Rolston, William D. Phillips
The advent of the laser as an intense, coherent light source gave birth to nonlinear optics, which now plays an important role in many areas of science and technology. One of the first applications of nonlinear optics was the production of coherent light of a new frequency by multi-wave mixing of several optical fields in a nonlinear medium, one whose refractive index depends on the intensity of the field. Until the experimental realization of Bose-Einstein Condensation (BEC) there had been no intense coherent source of matter-waves analogous to the optical laser. BEC has already been exploited to produce a matter-wave laser, leading us to the threshold of a new field of physics: nonlinear atom optics. Here we report the first experiment in nonlinear atom optics: the observation of coherent four wave mixing (4WM) in which three sodium matter waves mix to produce a fourth. We show the nonlinear dependence of the generated matter wave on the densities of input wave, a clear signature of a 4WM process.