Optical control of photoinduced nonlinear dynamics in nematic liquid-crystal films

We present the experimental results of the all-optical control of instabilities generated by laser irradiation in a nematic liquid-crystal film. Because of interactions with an incident linearly polarized optical field at a small angle of incidence, the system undergoes a sequence of successive bifurcations toward a stochastic regime. Control of the dynamics is achieved through the addition of a counterpropagating laser beam that is orthogonally polarized with respect to the inducing beam. The control strategy starts with putting the system into a given dynamic state through the incident beam and then switching on the control beam. Below the first bifurcation a weak control beam is enough to drive the system toward a fixed point, thus stopping the nonlinear dynamics. Above the first bifurcation, the behavior of the system strongly depends on the value of the intensity of the control beam used, and different dynamic regimes can be observed and investigated.