Nonlinear Effects and Patterns in a Cold Atomic Cloud

G. Labeyrie, G. L. Gattobigio, T. Chanelière +3 more

G. Labeyrie, T. Ackemann, Bruce G. Klappauf +3 more

G. Labeyrie, T. Ackemann, Bruce G. Klappauf +3 more

The nonlinear interaction between an optical medium and an electro-magnetic field can induce gradients in the index of refraction distribution, leading to patterns or filamentation in the most diverse nonlinear materials: solids, anisotropic soft matter (liquid crystals), cells containing thermal vapors, etc. One common difficulty in interpreting the results of these experiments and in comparing them to models is that the details of the interaction in these media are very complex. Cold atomic systems have well known linear and nonlinear optical properties, as illustrated in experiments on four wave mixing, electro-magnetic induced transparency or slow light propagation. Such samples are thus an excellent candidate for improving the comparison between theory and experiments, but so far to our knowledge no investigations on patterns have been performed in such systems.

A.A. Varfolomeev

G. Labeyrie, Ivor Krešić, Robin Kaiser +1 more

Cold atomic clouds constitute highly resonant nonlinear optical media, whose refractive index can easily be tuned via the light frequency. When subjected to a retroreflected laser beam and under appropriate conditions, the cloud undergoes spontaneous symmetry breaking, and spatial patterns develop in the transverse cross section of the beam. We investigate the impact of the sign of the light detuning from the atomic resonance on these patterns, thus directly comparing pattern formation for self-focusing and self-defocusing nonlinearities. Our observations emphasize the need for a ``diffractively thick'' medium description of the light-cloud interaction in which diffraction and nonlinear propagation inside the sample are taken into account.

Vincent Mançois