Dual Controlled Cross - Shaped Broadband Terahertz Absorber Based On Vanadium Oxide - Liquid Crystal Metamaterial

A low terahertz broadband tunable absorber was proposed, which was mainly composed of vanadium oxide (VO2) film and nematic liquid crystal layer. The simulation results show that the absorption can reach more than 90% in the range of 0.458 THz-1.1492 THz. With the vanadium oxide transited into metal state, the tuning absorber was realized. Since the dielectric constant of the nematic liquid crystal can be adjusted by bias voltage, without changing the intensity of absorption, but a shift in the bandwidth was observed. In addition, the structure designed in this paper was insensitive to incident light polarization and still remained high absorption at 60°. This tunable broadband metamaterial absorber can be used for attenuator and energy harvesting.

Dissipative structures induced by photoisomerization in a dye-doped nematic liquid crystal layer

Order–disorder phase transitions driven by temperature or light in soft matter materials exhibit complex dissipative structures. Here, we investigate the spatio-temporal phenomena induced by light in a dye-doped nematic liquid crystal layer. Experimentally, for planar anchoring of the nematic layer and high enough input power, photoisomerization processes induce a nematic–isotropic phase transition mediated by interface propagation between the two phases. In the case of a twisted nematic layer and for intermediate input power, the light induces a spatially modulated phase, which exhibits stripe patterns. The pattern originates as an instability mediated by interface propagation between the modulated and the homogeneous nematic states. Theoretically, the phase transition, emergence of stripe patterns and front dynamics are described on the basis of a proposed model for the dopant concentration coupled with the nematic order parameter. Numerical simulations show quite a fair agreement with the experimental observations. This article is part of the theme issue ‘Dissipative structures in matter out of equilibrium: from chemistry, photonics and biology (part 2)’.

SURFACE AZIMUTHAL ANCHORING ENERGY BETWEEN THE GRATING SURFACE AND NEMATIC LIQUID CRYSTAL LAYER STUDIED BY USING A GEOMETRIC MODEL

A simple geometric model is proposed for estimating the azimuthal anchoring energy between the sinusoidal relief grating surface and nematic liquid crystal layer of a liquid crystal display (LCD) device as a function of the grating height and grating pitch. The model parameters are determined experimentally, and the model is then used to predict the surface azimuthal anchoring energy for gratings with various pitches and heights. It is shown that a good agreement exists between the predicted results for the surface azimuthal anchoring energy and the experimental data. Moreover, a good agreement is also observed between the estimated results and those obtained from Berreman’s expression and finite element method (FEM) simulations, respectively. Overall, the experimental and numerical results show that for the nematic liquid crystal considered in the present study (4-n-pentyl-4’-cyanobiphenyl (5CB)), the surface azimuthal anchoring energy increases with an increasing grating height or a reducing grating pitch.