Analysis of gratings induced in azo-dye doped liquid crystals

• Main Authors: Frey, L. (Author), Kaczmarek, M. (Author), Jonathan, J-M (Author), Roosen, G. (Author)
• Format: Article
• Language: English
• Published: 2001.
• Subjects: Article
• Online Access: Get fulltext

 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.