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Two-beam energy exchange in a hybrid photorefractive inorganic-cholesteric cell

Two-beam energy exchange in a hybrid photorefractive inorganic-cholesteric cell
Two-beam energy exchange in a hybrid photorefractive inorganic-cholesteric cell
We develop a theoretical model to describe two-beam energy exchange in a hybrid photorefractive inorganic-cholesteric cell. A cholesteric LC cell is placed between two inorganic photorefractive windows. Weak and strong light beams are incident on the LC cell. The interfering light beams induce a periodic space-charge field in the photorefractive windows. This penetrates into the LC, inducing a diffraction grating written on the LC director. The theory calculates the energy gain of the weak beam, as a result of its interaction with the pump beam within the diffraction grating. In the theory, the flexoelectric mechanism for electric field-director coupling is a more important than the LC static dielectric anisotropy coupling. The flexoelectric polarization in the bulk LC follows from the initial director pretilt at the cell substrates and is the main physical mechanism governing the magnitude of the director grating and the two-beam coupling. The LC optics is described in the Bragg regime. Theoretical results for exponential gain coefficients have been compared with experimental results for hybrid cells filled with cholesteric mixtures TL205/CB15 and BL038/CB15. In order to reconcile theory and experiment, we require that (a) the magnitude of the director grating must be cubic rather than linear in the space-charge field, and (b) near the cell surface, nematic ordering must dominate. Within this paradigm, we are able to fit experimental data to theory for both cholesteric mixtures, subject to the use of some fitting parameters.
1542-1406
8-22
Reshetnyak, V. Yu
61e40ffa-1044-48ce-81aa-87a4eafb1765
Pinkevych, I.P.
07f566ed-7a1c-492d-a11e-3ff1e941e725
Cook, G.
fbf121a4-8973-4033-8759-81f517347b6e
Evans, D.R.
e53d4df7-2a26-49f0-8126-b6630165dfb3
Sluckin, T.J.
8dbb6b08-7034-4ae2-aa65-6b80072202f6
Reshetnyak, V. Yu
61e40ffa-1044-48ce-81aa-87a4eafb1765
Pinkevych, I.P.
07f566ed-7a1c-492d-a11e-3ff1e941e725
Cook, G.
fbf121a4-8973-4033-8759-81f517347b6e
Evans, D.R.
e53d4df7-2a26-49f0-8126-b6630165dfb3
Sluckin, T.J.
8dbb6b08-7034-4ae2-aa65-6b80072202f6

Reshetnyak, V. Yu, Pinkevych, I.P., Cook, G., Evans, D.R. and Sluckin, T.J. (2012) Two-beam energy exchange in a hybrid photorefractive inorganic-cholesteric cell. [in special issue: Proceedings of the 14th International Topical Meeting: Optics of Liquid Crystals (OLC 2011): Part II of III] Molecular Crystals and Liquid Crystals, 560 (1), 8-22. (doi:10.1080/15421406.2012.661950).

Record type: Article

Abstract

We develop a theoretical model to describe two-beam energy exchange in a hybrid photorefractive inorganic-cholesteric cell. A cholesteric LC cell is placed between two inorganic photorefractive windows. Weak and strong light beams are incident on the LC cell. The interfering light beams induce a periodic space-charge field in the photorefractive windows. This penetrates into the LC, inducing a diffraction grating written on the LC director. The theory calculates the energy gain of the weak beam, as a result of its interaction with the pump beam within the diffraction grating. In the theory, the flexoelectric mechanism for electric field-director coupling is a more important than the LC static dielectric anisotropy coupling. The flexoelectric polarization in the bulk LC follows from the initial director pretilt at the cell substrates and is the main physical mechanism governing the magnitude of the director grating and the two-beam coupling. The LC optics is described in the Bragg regime. Theoretical results for exponential gain coefficients have been compared with experimental results for hybrid cells filled with cholesteric mixtures TL205/CB15 and BL038/CB15. In order to reconcile theory and experiment, we require that (a) the magnitude of the director grating must be cubic rather than linear in the space-charge field, and (b) near the cell surface, nematic ordering must dominate. Within this paradigm, we are able to fit experimental data to theory for both cholesteric mixtures, subject to the use of some fitting parameters.

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More information

Published date: 2012
Organisations: Applied Mathematics

Identifiers

Local EPrints ID: 339056
URI: http://eprints.soton.ac.uk/id/eprint/339056
ISSN: 1542-1406
PURE UUID: 1c6324de-ea54-4988-9e06-fee5db961fa5
ORCID for T.J. Sluckin: ORCID iD orcid.org/0000-0002-9163-0061

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Date deposited: 22 May 2012 12:21
Last modified: 15 Mar 2024 02:32

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Contributors

Author: V. Yu Reshetnyak
Author: I.P. Pinkevych
Author: G. Cook
Author: D.R. Evans
Author: T.J. Sluckin ORCID iD

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