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 t he molecular director may be produced. At high beam intensities, the oscill ations break up into deterministic chaos. Although this effect has been kno wn 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 descr ibed by its two polar angles. We observed different dynamical regimes, depe nding on laser intensity: steady states, oscillations, rotations, and, at t he highest laser intensities, deterministic chaos. Moreover, the transition s between the oscillation and rotation regimes are characterized by intermi ttency.