Means of amplifying light in reactions of atoms with condensing gases

Wolfgang Ketterle

Summary form only given. Bose-Einstein condensed atomic gases are a new class of quantum fluids with many novel properties. We have studied collective modes and dissipation by perturbing the condensate with focused laser beams. The scattering of photons imparts momentum to the condensate and creates excitations. Consequently, the coherence and collective behavior of the condensate can strongly affect optical properties. We used light scattering to demonstrate that the coherence length of a condensate is equal to its physical size, and obtained dramatic evidence for the presence of correlated momentum excitations in the many-body condensate wavefunction. At higher laser intensity, a new form of superradiance was found which provided a gain mechanism for the generation of directed beams of atoms and light. This process amplified matter waves in a phase coherent way.

Crispin W. Gardiner

N. I. Shamrov

A multimode model of the superradiant Rayleigh scattering of light by the Bose-Einstein condensate of rarefied gases is proposed. A limiting transition to the widely used mean-field model is considered. The initial (linear) stage of the scattering process is considered with neglect of the diffraction in the multimode representation. A dependence of the order and number of the angular atomic modes on the parameters of the problem is determined.

Crispin W. Gardiner, P. Zoller

Gordon R. M. Robb, P. Johnston, W. J. Firth

Collective scattering of light due to atomic recoil, also known as collective atomic recoil lasing (CARL), occurs when a gas of atoms coherently scatters light from a pump laser via a collective instability. The scattering process can become unstable due to the atoms in the gas recoiling under the influence of the dynamic optical forces which arise due to the interference of the pump and scattered fields. The atoms move to form a spatially periodic density grating, which in turn amplifies the scattered field. This paper presents a theoretical analysis of CARL phenomena in degenerate ultracold gases of bosons and fermions. In the case of bosons i.e. in a Bose-Einstein Condensate (BEC),the effect of atom-atom interactions due to collisions on the CARL instability in the case of both attractive and repulsive condensates, is investigated. In the case of fermionic gases, the effect of Fermi pressure, is also presented. The linear and nonlinear evolution of the optical field and the atomic momentum distribution are considered for both cases.