Observation of cooperative Mie scattering from an ultracold atomic cloud

• Published in: Physical review. A, Atomic, molecular, and optical physics Vol. 82; no. 1
• Main Authors: Bender, H., Stehle, C., Slama, S., Kaiser, R., Piovella, N., Zimmermann, C., Courteille, Ph. W.
• Format: Journal Article
• Language: English
• Published: United States 26-07-2010
• Subjects: ANGULAR DISTRIBUTION; APPROXIMATIONS; ATOM COLLISIONS; ATOMIC AND MOLECULAR PHYSICS; ATOMS; BULK DENSITY; CALCULATION METHODS; COHERENT SCATTERING; COLLISIONS; DENSITY; DISTRIBUTION; EMISSION; ENERGY-LEVEL TRANSITIONS; FLUCTUATIONS; OPTICAL PROPERTIES; PHASE SHIFT; PHOTON COLLISIONS; PHOTON EMISSION; PHOTON-ATOM COLLISIONS; PHYSICAL PROPERTIES; RADIATION PRESSURE; RAYLEIGH SCATTERING; REFRACTIVE INDEX; SCATTERING; STIMULATED EMISSION; SUPERRADIANCE; VARIATIONS
• ISSN: 1050-2947; 1094-1622
• DOI: 10.1103/PhysRevA.82.011404

Scattering of light at a distribution of scatterers is an intrinsically cooperative process, which means that the scattering rate and the angular distribution of the scattered light are essentially governed by bulk properties of the distribution, such as its size, shape, and density, although local disorder and density fluctuations may have an important impact on the cooperativity. Via measurements of the radiation pressure force exerted by a far-detuned laser beam on a very small and dense cloud of ultracold atoms, we are able to identify the respective roles of superradiant acceleration of the scattering rate and of Mie scattering in the cooperative process. They lead, respectively, to a suppression or an enhancement of the radiation pressure force. We observe a maximum in the radiation pressure force as a function of the phase shift induced in the incident laser beam by the cloud's refractive index. The maximum marks the borderline of the validity of the Rayleigh-Debye-Gans approximation from a regime, where Mie scattering is more complex. Our observations thus help to clarify the intricate relationship between Rayleigh scattering of light at a coarse-grained ensemble of individual scatterers and Mie scattering at the bulk density distribution.