We report the analysis of the dynamical regimes induced in a homeotropically aligned nematic liquid crystal layer when a s-polarised laser beam acts at a small incident angle. For increasing light intensities these regimes are studied through an analysis performed on the variation of the polarisation state of a light probe beam. To measure with a good resolution the four Stokes parameters we use an experimental apparatus that include a pump-probe technique and a Four-Detector-Polarimeter (FDP). A preliminary description of the dynamical regimes, based on the analysis of the Fourier spectra, the autocorrelation functions and the attractors of the measured time series has been discussed. Moreover we calculated also the maximum Lyapunov exponent. For the last series of measurements this analysis suggest the presence of a transition towards chaos.