Dynamical regimes and motion intermittence induced by a laser beam in a nematic liquid crystal film

When an s-polarised laser beam shines on a homeotropically aligned film of nematic liquid crystal at small incidence angle, undamped oscillations of the molecular director may be produced. At high beam intensities, the oscillations break up into deterministic chaos. Although this effect has been known for a long time and the route to chaos has been qualitatively analysed, no detailed study of the director motion has been carried out. We designed an experimental apparatus to monitor the dynamics of the director, as described by its two polar angles. We observed different dynamical regimes, depending on laser intensity: steady states, oscillations, rotations, and, at the highest laser intensities, deterministic chaos. Moreover, the transitions between the oscillation and rotation regimes are characterized by intermittency.