We report the first experimental realization of spatial soliton formation by the Gaussian beam at 632.8 nm in the azobenzene liquid crystal (LC) layer with planar orientation of LC director. By appropriate anti-parallel rubbing of alignment layers on the upper and lower substrates of the cell LC molecules were oriented along the glass substrates nearly perpendicular to the input window of the cell with a small pre-tilt angle of ~2.60 relative to the beam propagation Z direction. The strong self-focusing effect and soliton formation for laser beam with vertical Y-polarization and beam diffraction for horizontal X-polarization have been observed in the absence of an external electric field. The physical model is considered which implies that the interaction of azobenzene molecules with a laser field is much stronger due to a larger coefficient of orientation nonlinearity compared to other LCs, as well as they are not rigidly anchored to the cell boundary. Thus the molecule alignment can be readily varied by a low-power laser field even for a small pre-tilt angle of molecules which leads to the refractive index change and beam self-focusing regime. The numerical integration of the propagation equation for spatial solitons describes the experimental data very well.
By illuminating a photo-alignment layer with two interfering UV laser beams with opposite circular polarization, a periodic alignment pattern is obtained for nematic liquid crystal. In a liquid crystal cell two substrates are used with periodic photo-alignment, with the periodicities perpendicular to each other. After filling with nematic liquid crystal the director obtains a 3D pattern with period twice that of the photo-alignment. The resulting 3D structure depends on the cell thickness (between 3 and 20 m) and the periodicity of the photo-alignment (also between 3 and 20 m). The director pattern can be estimated by performing numerical simulation with a Q-tensor method. The simulation results can be verified by polarization optical microscopy or by observing the diffraction properties of the structure. For a long range periodicity combined with a small period, the light is efficiently distributed over a small number of diffraction orders. The director pattern can be reoriented by applying a potential difference between the two substrate electrodes. Optical and electrical steering is investigated for devices with different dimensions.
We report the experimental investigation of image self-replication - Talbot effect with the use of 1- and 6 - fold rotational symmetry masks to create 3D intensity modulated light. These masks while having strong periodicity in azimuthal direction, are examples of multi-periodical and nearly periodical structures, respectively, along transverse XY directions. Since the Talbot image self-replication period in the axial direction depends on light wavelength and square of the structure periods, which are different in X-Y directions for 1-fold rotational symmetry mask, this gives a possibility to create the complex 3D light intensity distribution with different Talbot axial periodicity across the beam transverse plane. A cw single mode 532 nm, 100 mW laser beam was used in the experiment for formation of complex lattice beams. The observation of the transverse intensity patterns at multiple longitudinal positions will allow the construction of a whole 3D intensity distribution of the lattice beam. 3D intensity modulated light beams are promising for formation of crystalline and quasi-crystalline refractive index micro- and nano-structures in photorefractive materials.