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Analysis of gratings induced in azo-dye doped liquid crystals

Analysis of gratings induced in azo-dye doped liquid crystals
Analysis of gratings induced in azo-dye doped liquid crystals
We investigate the formation of photoinduced gratings in a homeotropic film of nematic liquid crystal doped with methyl red. Using a grating translation technique, we determine the time evolution of the amplitudes and phase shifts of both index and absorption modulations. With low writing intensities, a fast grating caused by photoisomerization of the dye competes with a slower grating, originating from a reorientation of the director. This slower grating only appears if the light polarization has a nonzero projection on the director, i.e. at oblique incidence. The grating decays in the dark. We suggest that its formation may be explained by a light-induced dielectric torque, rather than a photorefractive effect. With high intensities, an even slower grating is formed at normal incidence. We stipulate that it originates from a change in the anchoring parameters caused by the adsorption of photoisomerized dyes on the surfaces. The resulting reorientation of the director is permanent.
Doped liquid crystal, Gratings, Photoisomerization, Reorientation
91-94
Frey, L.
97657462-8489-499a-ae80-61d4827d86b4
Kaczmarek, M.
408ec59b-8dba-41c1-89d0-af846d1bf327
Jonathan, J-M.
89ddf039-b10d-4dd4-b5c4-1799e81f168a
Roosen, G.
fdc14bee-da70-4368-a37e-84a362644366
Frey, L.
97657462-8489-499a-ae80-61d4827d86b4
Kaczmarek, M.
408ec59b-8dba-41c1-89d0-af846d1bf327
Jonathan, J-M.
89ddf039-b10d-4dd4-b5c4-1799e81f168a
Roosen, G.
fdc14bee-da70-4368-a37e-84a362644366

Frey, L., Kaczmarek, M., Jonathan, J-M. and Roosen, G. (2001) Analysis of gratings induced in azo-dye doped liquid crystals. Optical Materials, 18 (1), 91-94. (doi:10.1016/S0925-3467(01)00139-2).

Record type: Article

Abstract

We investigate the formation of photoinduced gratings in a homeotropic film of nematic liquid crystal doped with methyl red. Using a grating translation technique, we determine the time evolution of the amplitudes and phase shifts of both index and absorption modulations. With low writing intensities, a fast grating caused by photoisomerization of the dye competes with a slower grating, originating from a reorientation of the director. This slower grating only appears if the light polarization has a nonzero projection on the director, i.e. at oblique incidence. The grating decays in the dark. We suggest that its formation may be explained by a light-induced dielectric torque, rather than a photorefractive effect. With high intensities, an even slower grating is formed at normal incidence. We stipulate that it originates from a change in the anchoring parameters caused by the adsorption of photoisomerized dyes on the surfaces. The resulting reorientation of the director is permanent.

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Published date: 2001
Keywords: Doped liquid crystal, Gratings, Photoisomerization, Reorientation

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Local EPrints ID: 15136
URI: https://eprints.soton.ac.uk/id/eprint/15136
PURE UUID: 45bbeb39-584a-4c28-8d51-749a509b3479

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Date deposited: 17 Mar 2005
Last modified: 18 Jul 2019 12:47

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