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.

Metasurfaces can be realized by organizing subwavelength elements (e.g., plasmonic nanoparticles) on a reflective surface covered with a dielectric layer. Such an array of resonators, acting collectively, can completely absorb the resulting resonant wavelength. Unfortunately, despite the excellent optical properties of metasurfaces, they lack the tunability to perform as adaptive optical components. To boost the utilization of metasurfaces and realize a new generation of dynamically controlled optical components, we report our recent finding based on the powerful combination of an innovative metasurface-optical absorber and nematic liquid crystals (NLCs). The metasurface consists of self-assembled silver nanocubes (AgNCs) immobilized on a 50 nm thick gold layer by using a polyelectrolyte multilayer as a dielectric spacer. The resulting optical absorbers show a well-defined reflection band centered in the near-infrared of the electromagnetic spectrum (750-770 nm), a very high absorption efficiency (∼60%) at the resonant wavelength, and an elevated photothermal efficiency estimated from the time constant value (34 s). Such a metasurface-based optical absorber, combined with an NLC layer, planarly aligned via a photoaligned top cover glass substrate, shows homogeneous NLC alignment and an absorption band photothermally tunable over approximately 46 nm. Detailed thermographic studies and spectroscopic investigations highlight the extraordinary capability of the active metasurface to be used as a light-controllable optical absorber.

We explore the limits of the photosensitive response of thin, 15 to 35 nm, films of complex azobenzene dyes. They show high refractive index, reaching 1.8, and significant photo-induced birefringence. We have successfully recorded strong, birefringent phase gratings with visible light and used the diffraction efficiency measurements to monitor their temporal evolution. The photo-induced gratings in such thin films were found not to be associated with any periodic surface relief, a typical feature in thicker azobenzene layers.

In this work the mechanisms leading to the enhancement of optical nonlinearity of nematic liquid crystalline material through localized heating by doping the liquid crystals (LCs) with gold nanoparticles (GNPs) are investigated. We present some experimental and theoretical results on the effect of voltage and nanoparticle concentration on the nonlinear response of GNP–LC suspensions. The optical nonlinearity of these systems is characterized by diffraction measurements and the second order nonlinear refractive index, n₂, is used to compare systems with different configurations and operating conditions. A theoretical model based on heat diffusion that takes into account the intensity and finite size of the incident beam, the nanoparticle concentration dependent absorbance of GNP doped LC systems and the presence of bounding substrates is developed and validated. We use the model to discuss the possibilities of further enhancing the optical nonlinearity.

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.

Ferroelectric nematic liquid crystals (FNLCs) combine long-range orientational order with macroscopic polarization. While their ferroelectric nematic phase has attracted considerable attention, the extent to which its polar character influences the non-polar nematic phase is not yet fully understood. Here, we investigate the non-polar nematic phase of the ferroelectric nematic mixture (MIX NF-P1) that emerges above 44 $$^\circ$$ C. In particular, we determine this liquid crystal interaction with alignment substrates by characterising the pretilt and polar anchoring. The pretilt is found to decrease with increasing temperature, while the polar anchoring remains strong throughout the non-polar nematic phase. Through dielectric and optical characterization, we also extract the dielectric coefficients, birefringence, voltage threshold, and the splay and bend elastic constants as a function of temperature. The voltage threshold is shown to be up to 20 times lower than in the conventional nematic liquid crystal E7, because the large dielectric anisotropy is retained in the non-polar nematic phase. The birefringence monotonically decreases with increasing temperature, while the elastic constants show temperature dependent behaviour consistent with trends reported for other FNLCs. This behavior differs markedly from those observed in conventional nematics, with the splay elastic constant remaining relatively constant. Thus, we demonstrate that the nematic phase of FNLCs cannot be regarded as a conventional nematic state and instead retains signatures of the underlying polar interactions. The combination of strong dielectric response and a low threshold voltage highlights the potential of these materials for high-speed electro-optic and photonic applications.