Heterogeneous liquid crystal (LC) systems are a new class of anisotropic materials which have been intensively studied
over the last decade. This article is concerned with two such systems: ferroelectric LC nano-suspensions and LCs with
polymer network. The significant implication of ferroelectric LC-colloids is the possibility of a significant reduction in
the threshold electric Fredericksz voltage. Here we present a theory of this phenomenon, which agrees qualitatively with
experiment. A second example of heterogeneous LC systems is a gradient-polymer-stabilized LC (G-PSLC) structure,
which has been proposed for a tunable-focus lens application. We report on theoretical model that describes the
dependence of the G-PSLC lens focal length on applied voltage. A previous model is improved by considering light
absorption during the polymerization. Again we find qualitative agreement with the experimental data.
We present theoretical study of optical singularity birth in a wave front of Gaussian light beam with initially smooth wave front. A linearly polarised Gaussian beam illuminates the homeotropically aligned nematic liquid crystal (NLC) cell. Strong
director anchoring at the cell walls is assumed. Equilibrium director profile is determined by the minimum of the total free energy. Functional minimum is found numerically solving Euler-Lagrange equations. We find the threshold intensity for light induced Frederiks-type transition. Utilizing the Huygens-Fresnel principle, quasi-isotropic and geometrical optics approximations we calculate the amplitude distribution in space for different distances from the cell. In the case of stigmatic Gaussian beam we have a ring of zero amplitude of the beam. Thus the edge dislocation of a wave front is born.
We report on theoretical study of optical singularity birth in a wave front of light beam with stigmatic and astigmatic Gaussian profile with intially smooth wave front passing through a homeotropically aligned nematic liquid crystal (NLC) cell. When a linearly polarized astigmatic Gaussian light beam illuminates the cell, the light induced Frederick's transition can be observed. Strong director anchoring at the cell walls is assumed. Ritz's variational method is used, i.e. the profile of director reorientation is considered to be similar to astigmatic Gaussian profile. Parameters of the trial function are calculated numerically. The threshold intensity of light beam is appeared to increase with increasing of asymmetry of the beam under the constant value of laser beam area and cell thickness. Utilizing the Huygens-Fresnel principle and geometrical optics approximation we calculate the amplitude distribution in space for different distances from the cell. It is obtained that in the case of stygmatic Gaussian beam incidence on NLC cell the circular edge dislocation is born.
We present a theoretical study of the possibility of optical singularity birth in a wave front of a laser beam passing through a homeotropically aligned nematic liquid crystal (LC) cell. There is not any distortion in the initial homogeneous homeotropic LC alignment at intensities below some threshold value. When light intensity becomes higher than this threshold value, LC director deviates from its initial orientation. Strong director anchoring at the cell walls is assumed. Inhomogeneous director profile leads to the modulation of refractive index which in its turn may be considered as a Gaussian lens formed in the LC cell. This lens gives birth to the phase singularities in coherent beam with initially smooth wave front. One can find the light field just after the LC cell at small values of director deviation in geometrical optics approximation, and utilizing the Huygens-Fresnel principle calculate spatial position of the phase singularity at near field as a function of intensity of the input beam. It was found that both radius of circular edge dislocation and its distance form the cell boundary decrease with increase of intensity of an incident beam.
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