Orientational Photorefractivity Bulk Effects

Bulk Space Charge Fidd Surface Charge Induced Field 

Owing to the impurities and other photochaige producing agents present in the liquid crystal cells, three forms of space-chaige fields are created within the bulk of the cell a typical photorefiactive component E and two other components i A and caused by the dielectric and conductivity anisotropies in conjunction with the reoriented director axis (see Fig. 8.13b). 

Following the treatment by Rudenko and sukhov, the photorefractive-like space-charge field induced by charge separation can be expressed as 

Meanwhile, the applied field E c along the z direction, in conjunction with the conductivity and dielectric anisotropies and the reoriented (by an angle 0) director axis, creates a transverse (along the x direction) electric field component, which in turn will further reorient the director axis. These space-charge fields are of the 

For small angle approximation, the above equations can be linearized to yield 

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Khoo, 1. C., Kan Chen, and Y. Wilhams. 2006. Orientational photorefractive effect in undoped and CdSe nano-rods doped nematic liquid crystal Bulk and interface contributions. J. Sel. Top. Quantum Electron 12(3) 443 50 see also Khoo, I. C., Yana Zhang Wilhams, B. Lewis, and T. Mallouk. 2005. Photorefractive CdSe and gold nanowire-doped hquid crystals and polymer-dispersed-liquid-crystal photonic crystals. Mol. Cryst Liq. Cryst. 446 233-244. 

Fig. 2. Oblique geometry tsqiically used for characterizing bulk photorefractive pol3miers. The magnified portion illustrates the orientational enhancement effect described in the text due to the modulated poling of the electro-optic chromophore in the combined Eb + Esc fields. The beam and grating geometry applies for both four-wave mixing (beams 1-4) and two-beam coupling (beams 1 and 2).

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