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Babinet complementary patterns of a spectrally tunable metamaterial incorporating a nematic liquid crystal is normally assumed to exhibit the same tuning range. Here we show that for a hybrid, liquid crystal-loaded metamaterial, the sensitivity of its terahertz resonances to the variations of the refractive index differs substantially for the two complementary patterns. This is due to a mismatch between the alignment of the liquid crystal and the direction of the local electric field induced in the metamaterial patterns. Furthermore, and more intriguingly, our experimental data indicate that it is possible to shift the resonance of the positive metamaterial pattern beyond the limit imposed by the alignment mismatch. Our analysis suggests that the observed anomalous frequency shift results from the orientational optical nonlinearity of a nematic liquid crystal.

Filamentous molecules tend to spontaneously assemble into liquid crystalline droplets with a tactoid morphology in environments with high concentration on non-adsorbing molecules. Tactoids of filamentous Pf bacteriophage, such as those produced by Pseudomonas aeruginosa, have been linked to increased antibiotic tolerance. We modelled this system and show that tactoids composed of filamentous Pf virions can lead to antibiotic tolerance by acting as an adsorptive diffusion barrier. The continuum model, reminiscent of descriptions of reactive diffusion in porous media, has been solved numerically and good agreement was found with the analytical results, obtained using a homogenisation approach. We find that the formation of tactoids significantly increases antibiotic diffusion times which may lead to stronger antibiotic resistance. [ABSTRACT FROM AUTHOR]

A method is described for forming both transient and permanent, 1- and 2-D gratings in nematic liquid crystals.The method can easily be controlled by externally applied ac fields.

Enhanced, photoactive response can be realised by integrating liquid crystals with photoalignment or photoconductive alignment layers. Such cells, asymmetric by design, need to be monitored for the stability and uniformity, especially in the regions exposed to light. In this work, we report on an integrated, versatile model and technique to characterise their core parameters as well as more subtle effects, such as the strength of anchoring energy. The snapshot method also provides two-dimensional maps of the cells' thickness, pretilt angle and uniformity. [ABSTRACT FROM AUTHOR]

Bidirectional oscillations can be supported in a single photorefractive ring resonator using Ce:BaTiO[sub 3]. We show that two oscillation beams can simultaneously propagate in opposite directions under different geometries. The difference in power between the two oscillation beams can reach two orders of magnitude and their stability depends on the pump beam angle of incidence and the crystal’s configuration. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Here, we report on the experimental demonstration that highly efficient self-induced spin-orbit optical vortex generation can be achieved by using standard liquid crystal materials and surface treatment agents. This is done by revisiting the recent attempt by Zolot'ko and coworkers to produce self-induced liquid crystal vortex plates using the dc electric field [I. A. Budagovsky, S. A. Shvetsov, and A. S. Zolot'ko, Mol. Cryst. Liq. Cryst. 637, 47 (2016)] that remains, so far, limited to moderate efficiencies. The phenomenon is the result of the self-back-action of light arising from the spontaneous creation of a liquid crystal topological defect. These results demonstrate photo-electric interface activation as a candidate towards the development of a self-adapted spin-orbit photonic toolbox, thus enabling agile management of the orbital angular momentum of light. [ABSTRACT FROM AUTHOR]

Achieving an efficient spectral tuning in liquid‐crystal (LC)‐loaded active photonic metamaterials has so far remained a challenge due to strong surface anchoring of LC molecules. This paper reports on a novel approach in the development of hybrid metamaterials that enables to overcome this problem and engage for the first time in‐plane switching of liquid‐crystal molecules on the nanoscale. Combined with the usual volume switching, it unlocks the full potential of the liquid crystals as a functional component of active metamaterial hybrids operating at optical frequencies. As a result, the resonant response of an active metasurface can now be controlled both in terms of its magnitude and wavelength with the spectral tunability approaching the theoretical limit of 9%. This mechanism of two‐way active switching of the hybrid metamaterial is also confirmed theoretically by simulating the distribution of the LC director around the metamaterial fabric. [ABSTRACT FROM AUTHOR]

It is found that ferroelectric nanoparticles synthesized by the sol-gel technique and milling can become charged during the fabrication. The balance between the concentrations of positively and negatively charged particles depends on the material, the treatment of particles, and concentration of the surfactant agent. It is suggested that the nanoparticles become charged due to their collisions during the milling and sonication. [ABSTRACT FROM AUTHOR]

Doping liquid crystals with nanoparticles is a widely accepted method to enhance liquid crystal's intrinsic properties. In this study, a quick and reliable method to characterise such colloidal suspensions using an optical multi-parameter analyser, a cross-polarised intensity measurement-based device, is presented. Suspensions characterised in this work are either plasmonic (azo-thiol gold AzoGNPs) or ferroelectric Sn2P2S6 (SPS) nanoparticles in nematic liquid crystals. The elastic constants and rotational viscosity showed nonlinear dependence on the concentration of AzoGNPs, initially increasing at lower concentrations and then decreasing at higher concentrations, indicating some degree of particle aggregation. For the SPS suspension, the elastic constant decreased with doping, while the rotational viscosity increased, in agreement with previous findings. Through viscosity measurements, the stability of SPS suspension over ten years is also highlighted. [ABSTRACT FROM AUTHOR]

We demonstrate the electro-optic control of self-confined beams via frequency modulation in dual-frequency nematic liquid crystals. Proper design of comb electrodes in a planar cell allows the maximization of the overall steering angle when only walk-off variations are used. A span angle as large as two times the maximum walk-off angle is achieved. [ABSTRACT FROM PUBLISHER]

We demonstrate frequency-controlled angular steering of light-induced solitary waveguides using dual frequency nematic liquid crystals. Specially designed comb-shaped electrodes allow the maximization of the in-plane electro-optic angular deviation of the soliton Poynting vector, modulating the resulting walk-off up to an overall deflection of 13° when the frequency of the applied voltage goes from 1 to 100 kHz. [ABSTRACT FROM AUTHOR]

We study the interaction of a spatial soliton waveguide with a voltage defined and electrically tuned interface in nematic liquid crystals, whereby the optic axis is reoriented through the use of patterned electrodes. We investigate refraction and total internal reflection of nematicon wavepackets, disclosing the role of anisotropy and obtaining a remarkable in-plane steering as large as 55°. [ABSTRACT FROM AUTHOR]

Spectroscopic ellipsometry is a technique especially well suited to measure the effective optical properties of a composite material. However, as the sample is optically thick and anisotropic, this technique loses its accuracy for two reasons: anisotropy means that two parameters have to be determined (ordinary and extraordinary indices) and optically thick means a large order of interference. In that case, several dielectric functions can emerge out of the fitting procedure with a similar mean square error and no criterion to discriminate the right solution. In this paper, we develop a methodology to overcome that drawback. It combines ellipsometry with refractometry. The same sample is used in a total internal reflection (TIR) setup and in a spectroscopic ellipsometer. The number of parameters to be determined by the fitting procedure is reduced in analysing two spectra, the correct final solution is found by using the TIR results both as initial values for the parameters and as check for the final dielectric function. A prefitting routine is developed to enter the right initial values in the fitting procedure and so to approach the right solution. As an example, this methodology is used to analyse the optical properties of BaTiO3 nanoparticles embedded in a nematic liquid crystal. Such a methodology can also be used to analyse experimentally the validity of the mixing laws, since ellipsometry gives the effective dielectric function and thus, can be compared to the dielectric function of the components of the mixture, as it is shown on the example of BaTiO3/nematic composite. [ABSTRACT FROM AUTHOR]

Light filaments or optical spatial solitons are self-confined (non-spreading) beams that originate from the balance between diffraction and self-focusing in nonlinear optical media (those with a response dependent on the level of excitation). Owing to their ability to self-trap as well as to guide weaker signals (even if differing in colour or modulation format) within the waveguides or ‘light-pipes’ they induce, optical spatial solitons could form the basis of future all-optical processing networks. One of the most interesting challenges in soliton propagation and engineering concerns light filaments incident on linear/nonlinear or nonlinear/nonlinear interfaces. Here we report the robust propagation, refraction and reflection of optical spatial solitons at the interface between two regions of a nematic liquid crystal. The ability to independently tune the optical properties of each region enables us to steer the beams by refraction and total internal reflection by as much as −18 and +22 degrees, respectively. Moreover, the extended (nonlocal) and anisotropic response of our system supports polarization healing of the solitons across the interface as well as non-specular filament reflection. Finally, exploiting the inherent and all-optically tunable birefringence, we demonstrate unprecedented nonlinear Goos–Hänchen lateral shifts in excess of 0.5 mm. [ABSTRACT FROM AUTHOR]

The dynamics of energy transfer in photoconductive polymer liquid crystal structures can contain important information on interface effects and surface electric fields contributing to the strength of liquid crystal reorientation gratings. The characteristic, transient effects observed during switching on and off of incident light or electric field can be explained by the presence of surface screening layers. Screening layers play an important role in the reorientation of liquid crystal director in cells with different alignment layers. Strong screening of external DC field is present not only in cells with a photoconductive polymer (56 V), but in standard cells with thicker (0.3 µm) polyimide, aligning layers. [ABSTRACT FROM AUTHOR]

We present characteristics of liquid crystal reorientation in cells with alignment layers made of different poly(vinyl)-type polymers. Mechanically-rubbed poly(N-vinyl carbazole) (PVK) produces planar alignment of liquid crystals with easy axis orthogonal to the rubbing direction and zero pretilt angle. Doping PVK with C[sub 60] makes this liquid crystal–polymer system extremely photosensitive for visible wavelengths. Illumination with a Gaussian beam reveals a complex structure of patterns of reoriented liquid crystal molecules. Using poly(vinyl-cinnamate) (PVCN), exposed to UV light, a periodic alignment of liquid crystals can be achieved via this all-optical method. [ABSTRACT FROM AUTHOR]

Using an external voltage and interdigitated electrodes in a liquid crystalline cell, we demonstrate tunable steering of light beams and spatial solitons without the detrimental walk-off out of the plane of propagation. The results agree well with a simple model describing birefringence and reorientation in uniaxial nematic liquid crystals. [ABSTRACT FROM AUTHOR]

Single crystals of z-cut 0.05% Fe:doped lithium niobate (Fe:LiNbO[sub 3]), have been etched in a mixture of HF and HNO[sub 3] acids, under simultaneous illumination from a ∼100 mW 488 nm wavelength Ar ion laser light source, focused to power densities of ∼50 W cm-2 at the crystal surface exposed to the etchant. Etching is partially inhibited in illuminated regions, and the degree of inhibition shows a systematic latency: sites illuminated early in the etch run resist further etching even after the light is removed. Etched structures additionally exhibit regular periodic features of ∼0.5 μm scale length. Details of these structures are shown, and the latent etching effect is discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We investigated bistability with light beams in reorientational nematic liquid crystals. For a range of input powers, beams can propagate as either diffracting or self-trapped, the latter corresponding to spatial solitons. The first-order transition in samples exhibiting abrupt self-focusing with a threshold is in agreement with a simple model. [ABSTRACT FROM AUTHOR]