Coherent light scattering by interacting two-level atoms: experiment & theory

Yvan R. P. Sortais

Terumi Chikama, Kazuhiko Saikawa, Ryogo Kubo

In order to investigate the effect of perturbation caused by the interaction of a two-level atom with its environment on the coherency of light scattered by the atom when it is irradiated by an intense radiation, Mollow's theory is generalized to include a random modulation of the resonance frequency as well as fluctuations of the incident field. Expressions for the power spectrum, the total intensity, the coherent scattering intensity and the broad Rayleigh scattering intensity are derived. Some general aspects of the problem are discussed.

Haider R. Zaidi

A theory of resonant light scattering from two level atoms in a gas is developed for an arbitrarily strong pump field. The Doppler effect and two body foreign gas collisions are considered. Elastic, inelastic (upward and downward), and the velocity changing collisions are retained in the general formulation. The impact approximation is not made, and the expressions for all (field dependent) collision rates are generated internally. Particular attention is paid to the lower state interaction, and a more complete parameterization of the theory is achieved. The general theory is non-Markovian and the quantum regression theorem is not used; it reduces to existing theories in special cases. It is shown that the coherent scattering is not a general property of the system if the lower state interaction is present; the "coherent" component acquires a small, but nonzero, width in the strong field region. This width could provide information about some new collision parameters.

Oleg N. Gadomsky, V. R. Nagibarov

P. van der Straten, Harold J. Metcalf

Stephan Jennewein, Ludovic Brossard, Yvan R. P. Sortais +4 more

We measure the coherent scattering of low-intensity, near-resonant light by a cloud of laser-cooled two-level rubidium atoms with a size comparable to the wavelength of light. We isolate a two-level atomic structure by applying a 300-G magnetic field. We measure both the temporal and the steady-state coherent optical response of the cloud for various detunings of the laser and for atom numbers ranging from 5 to 100. We compare our results to a microscopic coupled-dipole model and to a multimode, paraxial Maxwell-Bloch model. In the low-intensity regime, both models are in excellent agreement, thus validating the Maxwell-Bloch model. Comparing to the data, the models are found in very good agreement for relatively low densities ($n/{k}^{3}\ensuremath{\lesssim}0.1$), while significant deviations start to occur at higher density. This disagreement indicates that light scattering in dense, cold atomic ensembles is still not quantitatively understood, even in pristine experimental conditions.