Induced modulation instability and recurrence in nematic liquid crystals.

We study induced modulation instability in a nematic liquid crystal cell. Two broad elliptical beams along one direction are launched into the cell. The two beams have slightly different angle in order to create a sinusoidally varying intensity at the entrance of the cell. In this way, the gain of perturbations with different spatial frequency is investigated. The evolution of the optical pattern, for certain conditions, shows a recurrence of the signal. We believe that this is the manifestation of the Fermi-Pasta- Ulam recurrence and to the best of our knowledge, the first experimental observation of this phenomenon in the spatial optical domain. Numerical simulations show a good agreement with the experimental findings.