EXPERIMENTAL-STUDY OF THE MOLECULAR-REORIENTATION INDUCED BY THE ORDINARY WAVE IN A NEMATIC LIQUID-CRYSTAL FILM

When an s-polarized laser beam impinges on a homeotropically aligned f ilm of nematic liquid crystal at small incident angle, undamped oscill ations of the molecular director may be produced. At high beam intensi ties 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 actual molecular dir ector motion has been carried out. We have designed an experimental ap paratus to monitor the dynamics of the molecular director, as describe d by its two polar angles. We observed different dynamical regimes, de pending on the laser intensity: steady states, ocillations, rotation a nd, at the highest laser intensities, deterministic chaos. Moreover, t he transitions between the oscillation and rotation regimes are charac terized by intermittency.