Abstract
We develop a theory describing energy gain when two light beams intersect in a hybrid nematic liquid crystal (LC) cell with photorefractive crystalline substrates. A periodic space-charge field induced by interfering light beams in the photorefractive substrates penetrates into the LC layer and reorients the director. We account for two main mechanisms of the LC director reorientation: the interaction of the photorefractive field with the LC flexopolarization and the director easy axis at the cell boundaries. It is shown that the resulting director grating is a sum of two in-phase gratings: the flexoelectric effect driven grating and the boundary-driven grating. Each light beam diffracts from the induced gratings leading to an energy exchange between beams. We evaluate the signal beam gain coefficient and analyze its dependence on the director anchoring energy and the magnitude of the director easy axis modulation.
Highlights
Energy transfer between light beams due to the photorefractive effect in solid inorganic crystals is a well-known effect.[1]
II we introduce a model of the hybrid nematic cell placed in the interference pattern of two incident light beams, and derive and solve equations for the liquid crystal (LC) director profile subject to the space-charge electric field
As it is seen from eq (12), the director spatial profile is a result of the summation of two inphase gratings induced in the LC: 1) the “flexoelectric” grating arising due to the photorefractive field coupling with the LC flexopolarization, and 2) the “boundary-driven” grating arising due to the director easy axis modulation caused by the photorefractive space-charge field
Summary
Energy transfer between light beams due to the photorefractive effect in solid inorganic crystals is a well-known effect.[1]. The space charges create a spatially modulated electric field (i.e. space-charge field), which penetrates into the adjacent LC layer, causing a director-modulationinduced grating of the LC permittivity Both incident light beams propagate across the LC sample and diffract on the grating. Until recently it has only been possible to operate in the Raman-Nath regime, for which the sample thickness is less than the grating thickness In this case the coupled beams generate multiple order diffracted beams that leads to limited technological applicability of the effect.[13] in papers[10,14] it has been shown that inorganic photorefractive crystals can support efficient space-charge field generation in samples with thicknesses greater than the grating thickness. The authors of paper[17] proposed that director grating formation in hybrid organic-inorganic photorefractives is governed by the interaction of the space-charge field with the LC flexoelectric polarization, rather than by static dielectric anisotropy coupling.
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