Molecular Crystals and Liquid Crystals Vol. 412

LC Alignment Controlled by Photoordering and Photorefraction in a Command Substrate

Abstract:

As command substrates in liquid crystal (LC) panels, azopolymer films have been widely studied over past decade. These studies were mainly caused by photoordering and photorefraction effects allowing to control LC alignment. Earlier, the mentioned effects were used separately. In the present study, a layer of azopolymer acts both as photoaligning and photorefractive substrate. The photoordering effect is used to align LCs homogeneously, whereas effect of the specific photorefraction is employed to modify boundary conditions. The latter ones were spatially modulated by the sample exposure to interference patterns formed by two coherent laser beams. Multiple orders of diffraction are observed in samples tilted with respect to the beam incidence bisector when the samples are biased by a dc external electric field with the intensity close to the Frederiks threshold. Possible grating recording mechanisms are discussed.
LC Alignment Controlled by Photoordering and Photorefraction in a Command Substrate

Molecular Crystals and Liquid Crystals Vol. 421

Large Optical Torque Enhancement By Oligothiophene Dye In A Nematic Liquid Crystal Host

Abstract:

We have studied the nonlinear optical response of the nematic liquid crystal E7 doped with the oligothiophene dye TR5. Z-scan measurements showed a large positive(self-focusing)nonlinearity, originating in director reorientation. The oligothiophene dye enhances the nonlinearity of the host, in a similar manner to that of azo- and anthraquinone dyes in guest-host systems which exhibit the Janossy effect. The enhancement factor is unusually large; our TR5-E7 system showed as large a dye-induced optical torque enhancement factor as any observed in a guest-host system. Here we present our experimental results, determine the enhancement factor, and hypothesize that the dominant mechanism involves a photo-induced decrease in the orientational mobility of the dye molecules.

Large Optical Torque Enhancement By Oligothiophene Dye In A Nematic Liquid Crystal Host