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Owing to the passive nature of liquid crystal (LC) materials, achieving luminous displays using pure LC materials is challenging. In addition, it is difficult to achieve a fast switching time using pristine ferroelectric LC devices without compromising their cell thickness. Herein, we have developed a fast switching and highly luminescent electro-optical device by dispersing a minute concentration of bimetallic nanoparticles (Au@Ag NPs) having a spherical gold core and a silver shell within a ferroelectric liquid crystal (FLC) host matrix, ZLI3654. Au@Ag core–shell NPs having synergic attributes of both counterparts were successfully synthesized by a facile seed-mediated route. The Au core helps to tune the shape of the Ag shell and provides enhanced electron density as well as improved stability against oxidation. Introducing nanoparticles induces little structural modifications to the host FLC, resulting in an improvement in the mesogenic alignment. Interestingly, ∼29-fold enhancement in the photoluminescence (PL) intensity is observed on dispersing 0.25 wt% of Au@Ag NPs into the FLC host matrix. The enhanced electromagnetic field in the FLC-nanocomposite is attributed to the Localized Surface Plasmon Resonance of Au@Ag NPs, which strengthens the photon absorption rates by the FLC molecules, culminating in the massive enrichment of the PL intensity. In addition, the improved localized electric field inside the FLC device led to a noticeable enhancement in the spontaneous polarization, dielectric permittivity, and, most interestingly, ∼53% fastening in the switching time at an optimum concentration (0.25 wt%) of Au@Ag NPs. The improved electro-optical parameters of the Au@Ag NPs/FLC composite have been compared with the performance of both pristine Au NPs/FLC and Ag NPs/FLC composites, respectively, for the comprehensiveness of the study. The present study paves a systematic way to develop FLC-based advanced electro-optical devices with faster switching and higher luminescence properties. [ABSTRACT FROM AUTHOR]

This study investigates the influence of Grandjean–Cano disclinations on the cholesteric-blue phase I (Ch-BPI) phase transition, revealing the pivotal role of defects in the phase transition of liquid crystals (LCs). We prepared the disclinations by wedge cells or parallel cells with an alignment pattern and demonstrated that the disclinations induce a phase transition in Ch-BPI. Furthermore, we demonstrated the control of the BPI appearance areas by utilizing this property. This defect-induced transition technique not only provides a novel method for controlling BPI orientation, but also offers insights into soft material crystal growth, suggesting potential applications in new BPLC-based device development.

Integer winding disclinations are unstable in a nematic and are removed by an ‘escape into the third dimension’, resulting in a non-singular texture. This process is frustrated in a cholesteric material due to the requirement of maintaining a uniform handedness and instead results in the formation of strings of point defects, as well as complex three-dimensional solitons such as heliknotons that consist of linked dislocations. We give a complete description of this frustration using methods of contact topology. Furthermore, we describe how this frustration can be exploited to stabilise regions of the material where the handedness differs from the preferred handedness. These ‘twist solitons’ are stable in numerical simulation and are a new form of topological defect in cholesteric materials that have not previously been studied.

Hydrogen-bonded polar nematic liquid crystal series with the general formula n OBAF (n = 7â€"12) is studied. The mesomorphic characterization is demonstrated through differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The complexes with short alkyl chains (n = 7, 8) present a wide nematic range and monotropic smectic F mesophase, whereas the longer alkyl chain (n = 10â€"12) analogues show high melting and low clearing mesomorphic liquid crystals. The thermal range of the mesophase and the birefringence increase with chain length decreasing. Furthermore, the effect of the nanoparticles (LiNbO3) on the thermal and the electrical behavior of 8OBAF are investigated. The presence of LiNbO3 nanoparticles increases the conductivity and reduces the resistivity of the complex. [ABSTRACT FROM AUTHOR]

We introduce a phase field crystal (PFC) model for particles with n -fold rotational symmetry in two dimensions. Our approach is based on a free energy functional that depends on the reduced one-particle density, the strength of the orientation, and the direction of the orientation, where all these order parameters depend on the position. The functional is constructed such that for particles with axial symmetry (i.e. n = 2) the PFC model for liquid crystals as introduced by Löwen (2010 J. Phys.: Condens. Matter 22 364105) is recovered. We discuss the stability of the functional and explore phases that occur for 1 ⩽ n ⩽ 6. In addition to isotropic, nematic, stripe, and triangular order, we also observe cluster crystals with square, rhombic, honeycomb, and even quasicrystalline symmetry. The n -fold symmetry of the particles corresponds to the one that can be realized for colloids with symmetrically arranged patches. We explain how both, repulsive as well as attractive patches, are described in our model. [ABSTRACT FROM AUTHOR]

In this paper, a systematic design method for tunable metasurface based on liquid crystal (LC) is proposed, which exhibits the property of polarization selection. A compact LC-based meta-atom with a dimension of 0.12 λ × 0.12 λ is designed. The metasurface element consists of a pair of planar metallic structures, between which the LC is sandwiched. The equivalent circuit, electric field distribution, and current distribution elaborate on the design method and operating principle of the LC-based metasurface in detail. Full wave simulations show that the tunable metasurface provides bandpass and bandstop characteristics for TE and TM polarization, respectively. The center frequencies of the passband and stopband are tuned from 10.88 GHz to 10.3 GHz and 10.90 GHz to 10.18 GHz, and the tuning range reaches up to 5.5% and 6.8%, respectively. Compared with the existing work, tunability is introduced while maintaining the polarization selection characteristics. Moreover, frequency responses of the LC-based metasurface under various incident angles from 0° to 70° are kept to be stable for arbitrary LC states. In addition, a prototype sample is designed, fabricated, and measured to verify the proposed design method. [ABSTRACT FROM AUTHOR]

Composed of microscopic layers that stack along one direction while maintaining fluid-like positional disorder within layers, smectics are excellent systems for exploring topology, defects and geometric memory in complex confining geometries. However, the coexistence of crystalline-like characteristics in one direction and fluid-like disorder within layers makes lamellar liquid crystals notoriously difficult to modelâ€"especially in the presence of defects and large distortions. Nematic properties of smectics can be comprehensively described by the Q ̲ ̲ -tensor; however, lamellar order can exist independent of nematic alignment. To capture the features of the smectic layering alone, we develop a phenomenological Landau theory for a complex-tensor order parameter E ̲ ̲ , which is capable of describing the local degree of lamellar ordering, layer displacement, and orientation of the layers. This theory accounts for both parallel and perpendicular elastic contributions. In addition to resolving the potential ambiguities inherent to complex scalar order parameter models, this model reduces to previously employed models of simple smectics, and opens new possibilities for numerical studies on smectics possessing many defects, within complex geometries and under extreme confinement. [ABSTRACT FROM AUTHOR]

A switchable contact lens prototype was fabricated and tested with integrated off the shelf electronic components to drive a liquid crystal (LC) active lens element. This prototype was capable of changing its focal power by an average of +1.9D, but a maximum of +3.2 ± 0.2D was also measured. Switchable focus contact lenses are intended to help restore functional near and intermediate vision accommodation to those suffering from presbyopia, an inevitable age-related eye condition. The custom poly-methyl-methacrylate contact lens substrates used in this prototype are equivalent to commercially available scleral contact lenses. It was discovered that more careful design considerations are needed when at least one of the substrates is <100 µ m thick (which is needed for a final device). Without these design considerations, the switchable focal power of the lens is susceptible to change as the LC insert layer is able to flex. The prototype has an on-board electronics platform which was self-powered with a battery. Illuminating the electronics package with a 600 Hz infrared signal switched the device on, which passed an AC voltage to the electrodes of the contact lens, reorientating the director of the LC with an electric field. To our knowledge, this is the first demonstration of a battery powered and wirelessly triggered smart contact lens for the treatment of presbyopia. [ABSTRACT FROM AUTHOR]

In this work, we developed a lipid mixture based on phytantriol / polyoxyethylene surfactant (Brij-56) that forms a Im 3 m symmetry bicontinuous cubic phase based on the Schwartz primitive surface (Q II P ), from which we templated highly ordered 3D nanoporous platinum with a novel ‘single primitive’ morphology (Pm3m symmetry). The Q II P template phase is obtained by incorporation of 17.5% w/w Brij-56 (C16EO10) (a type-I surfactant) into phytantriol under excess hydration conditions. Phytantriol alone forms the double diamond Q II D (Pn3m) phase, and in previous studies incorporating Brij-56 at different compositions the cubic phase maintained this morphology, but increased its lattice parameter; mesoporous metals templated from these Q II D lipid templates all exhibited the ‘single diamond’ (Fd 3 m) morphology. In contrast, the current paper presents the availability of our Q II P cubic phases to template nanoporous materials of single primitive Pm3m morphology via chemical and electrochemical methods. To explore the structure porosity and morphological features of the templated Pt material, x-ray scattering and transmission electron microscopy are used. The resulting 3D nanoporous Pt materials are found to exhibit a regular network of Pt nanowires of ∼4 nm in diameter with a unit cell dimension of 14.8 ± 0.8 nm, reflecting the aqueous network within the Q II P template. [ABSTRACT FROM AUTHOR]

We present a fast-switching liquid crystal device comprising fringe field switching (FFS) electrode structure deposited onto one of the device substrates. Initially, the liquid crystal in the device has a homeotropic alignment. The generated periodic electric field by the FFS electrode results in a periodic splay/bend elastic deformation, thus giving rise to flexoelectric polarization along the substrate normal. At low applied voltages, this periodic elastic deformation, is substantially localized in a very thin portion of the liquid crystal layer adjacent to the substrate surface bearing the electrode and it is stabilized by a polymer network. Thus, the flexoelectric polarization becomes permanently present in the device and has non-zero value at field-off state. The polymer network with splay/bend configuration occupies very small part of the liquid crystal layer (∼0.5 μm), which is thinner than the light wavelength and therefore is optically invisible. Simultaneously with the formation of the polymer network, possessing splay/bend configuration, a polymer network with polymeric bundles oriented preferably along the substrates' normal is formed. As we will show, the presence of the polymer network, consisting of surface and bulk parts, reduces substantially the switching times of the liquid crystal device more than one order bringing them to μs range. [ABSTRACT FROM AUTHOR]

Active control of near-field radiative heat transfer (NFRHT) is enabled by magneto-optical (MO) materials with great application potential. Aside from MO materials, liquid crystals (LCs) can serve as an excellent host material to modulate optical properties in the mid infrared under magnetic field. Here, we theoretically investigate the magnetic-field control of NFRHT between two LC-based MO metamaterials consisting of InSb nanoparticles in the form of single strand chains dispersed in LC. We find that a relatively weak magnetic field can control the heat flux due to the Freedericksz transition of LC. With the increase of the magnetic field, MO response of InSb leads to a more pronounced thermal modulation. The intrinsic and the magnetization-induced hyperbolic modes, along with the dipole resonances of the particles, play a dominant role in NFRHT. Moreover, we discuss the influences of different aggregation forms of particles and volume filling fractions on the heat transfer. Our study can endow the modulation of NFRHT with an alternative practical and feasible solution. [ABSTRACT FROM AUTHOR]

A tunable liquid crystal (LC) polarization rotator that can rotate the polarization axis of linearly-polarized broadband light is achieved by using an asymmetrically-anchored negative LC cell. Interdigitated electrodes are used to apply an in-plane field to control the twist angle. The use of the asymmetrical anchoring in the LC cell enables continuous change of the twist angle by increasing the applied electric field. For uniform transmission, we used an LC that has negative dielectric anisotropy to avoid tilting of LC molecules by the vertical component of the electric field. We theoretically and experimentally confirmed that the fabricated LC cell could continuously change the twist angle and rotate the polarization axis of the linearly-polarized broadband incident light. [ABSTRACT FROM AUTHOR]

This paper presents a non-intrusive measurement technique for the simultaneous assessment of the three-dimensional (3D) velocity and temperature fields in thermal convection. The technique is based on the combination of tomographic particle image velocimetry and particle image thermometry. Thermochromic liquid crystal particles serve simultaneously as both flow tracers and thermometers. The velocity fields were measured in a volume of 62 500 cm3 and the temperature fields in a subvolume of 20 000 cm3. Turbulent Rayleigh–Bénard convection in a water-glycol mixture at and was used as a model system to measure the instantaneous 3D velocity and temperature fields at the same time. Uncertainties of mm s−1 for the velocity and K for the temperature measurement were estimated corresponding to dynamic ranges of 24 and 21 levels, respectively. Correlating the measured temperature and velocity fields, it is shown that the obtained large-scale structure reflects a region of warm rising fluid which is well-known from the literature. [ABSTRACT FROM AUTHOR]

A novel quad-polarization reconfigurable holographic artificial impedance surface that exploits the tunable dielectric permittivity of nematic liquid crystal is proposed. The arc-shaped strip is introduced and serves as the fundamental element, and further combined with holographic modulation, electromagnetic radiation at the terahertz band is realized. By partitioning the circular surface into several sectors, studies show that just two impedance values for each sector are enough to reconfigure among different polarizations. The presented demonstrator has a radius of 4.3λ0, where λ0 is the wavelength in free space at 1.25 THz, and is excited by a monopole. It can be dynamically reconfigured among vertical linear polarization, horizontal linear polarization, right-hand circular polarization, and left-hand circular polarization at the boresight. [ABSTRACT FROM AUTHOR]

In this paper, a design method for tunable liquid crystal (LC)-based frequency selective surface (FSS) with the compact unit cell, large tuning range, and the passband of flat-top and sharp roll-off is proposed. A very compact LC-based bandpass FSS unit cell with the dimension of 0.077 λ × 0.077 λ is designed based on a pair of planar vortex-shaped metallic structure with two large parallel patches, between which the LC is sandwiched. Results show that the central frequency of the FSS is tuned from 11.56 to 12.58 GHz, and the tuning range reaches up to 8.5%. In order to obtain the transmission characteristics of flat-top and sharp roll-off, a double-layer structure is proposed and combined with the LC-based FSS design. Theoretical analyses are conducted to declare the working principle of the double-layer LC-based FSS. A prototype sample for the double-layer LC-based FSS is designed and fabricated. Results show that the double-layer LC-based FSS structure achieves frequency selective characteristics with a flat-top passband of about 450 MHz and sharp roll-off for arbitrary LC states with −15 dB rectangle coefficient of 2.44 for arbitrary LC states. Moreover, stable frequency responses of the double-layer LC-based FSS under various incident angles from 0° to 45° are obtained for arbitrary LC states. [ABSTRACT FROM AUTHOR]

When a liquid crystal elastomer layer is bonded to an elastic layer, it creates a bilayer with interesting properties that can be activated by applying traction at the boundaries or by optothermal stimulation. Here, we examine wrinkling responses in three-dimensional nonlinear systems containing a monodomain liquid crystal elastomer layer and a homogeneous isotropic incompressible hyperelastic layer, such that one layer is thin compared to the other. The wrinkling is caused by a combination of mechanical forces and external stimuli. To illustrate the general theory, which is valid for a range of bilayer systems and deformations, we assume that the nematic director is uniformly aligned parallel to the interface between the two layers, and that biaxial forces act either parallel or perpendicular to the director. We then perform a linear stability analysis and determine the critical wave number and stretch ratio for the onset of wrinkling. In addition, we demonstrate that a plate model for the thin layer is also applicable when this is much stiffer than the substrate. [ABSTRACT FROM AUTHOR]

We investigate existence and uniqueness for the liquid crystal flow driven by colored noise on the two-dimensional torus. After giving a natural uniqueness criterion, we prove local solvability in Lp-based spaces, for every p > 2. Thanks to a bootstrap principle together with a Gyöngy–Krylov-type compactness argument, this will ultimately lead us to prove the existence of a particular class of global solutions which are partially regular, strong in the probabilistic sense, and taking values in the 'critical space' L2 × H1. [ABSTRACT FROM AUTHOR]

We give a description of the intrinsic geometry of elastic distortions in three-dimensional nematic liquid crystals and establish necessary and sufficient conditions for a set of functions to represent these distortions by describing how they couple to the curvature tensor. We demonstrate that, in contrast to the situation in two dimensions, the first-order gradients of the director alone are not sufficient for full reconstruction of the director field from its intrinsic geometry: it is necessary to provide additional information about the second-order director gradients. We describe several different methods by which the director field may be reconstructed from its intrinsic geometry. Finally, we discuss the coupling between individual distortions and curvature from the perspective of Lie algebras and groups and describe homogeneous spaces on which pure modes of distortion can be realised. [ABSTRACT FROM AUTHOR]

We introduce a wide class of singular inhomogeneously polarized beams characterized by a nonuniform rotation rate of the local polarization azimuth about a C- or a V-point. They are obtained by adding an extra phase modulation with an m-fold rotational symmetry to the helical wavefronts underpinning Poincaré beams. The resulting modulated Poincaré beams have been theoretically studied and experimentally generated using tailored space-varying-axis plates based on liquid crystals. [ABSTRACT FROM AUTHOR]

In this paper, we will establish the global existence of a suitable weak solution to the Erickson–Leslie system modelling hydrodynamics of nematic liquid crystal flows with kinematic transports for molecules of various shapes in , which is smooth away from a closed set of (parabolic) Hausdorff dimension at most. [ABSTRACT FROM AUTHOR]

We present an experimental off-axis optical holographic scheme employing a digital micromirror device (DMD) as projecting media instead of a liquid crystal spatial light modulator (SLM). The DMD allows projecting information through light reflection. We perform holographic recording in the Fourier and the Fresnel domains under similar experimental configurations to test our experimental scheme and verify the DMD performance as a binary amplitude SLM. For the digital holographic recovery process of Fourier holograms, we applied a non-linear modification that allows reducing the degradation in the recovered data. We also implement a multiplexing protocol enabling the packaging of an entire holographic dynamic scene into a single data. Furthermore, we use QR codes as information containers to achieve noise-free information recovery after holographic reconstruction. Experimental results demonstrate the viability and versatility of a DMD in an experimental holographic scheme. [ABSTRACT FROM AUTHOR]

The Lebwohl–Lasher model describes the isotropic–nematic transition in liquid crystals. In two dimensions, where its continuous symmetry cannot break spontaneously, it is investigated numerically since decades to verify, in particular, the conjecture of a topological transition leading to a nematic phase with quasi-long-range order. We use scale invariant scattering theory to exactly determine the renormalization group fixed points in the general case of N director components (RPN−1 model), which yields the Lebwohl–Lasher model for N = 3. For N > 2 we show the absence of quasi-long-range order and the presence of a zero temperature critical point in the universality class of the O(N(N + 1)/2 − 1) model. For N = 2 the fixed point equations yield the Berezinskii–Kosterlitz–Thouless transition required by the correspondence RP1 ∼ O(2). [ABSTRACT FROM AUTHOR]

We experimentally demonstrate the possibility to modulate the second harmonic (SH) power emitted by nonlinear AlGaAs metasurfaces embedded in a liquid crystal (LC) matrix. This result is obtained by changing the relative in-plane orientation between the LC director and the linear polarization of the light at the excitation wavelength. According to numerical simulations, second-harmonic is efficiently radiated by the metasurfaces thanks to the sizeable second-order susceptibility of the material and the resonant excitation of either electric or magnetic dipole field distributions inside each meta-atom at the illuminating fundamental wavelength. This resonant behavior strongly depends on the geometric parameters, the crystallographic orientation, and the anisotropy of the metasurface, which can be optimized to modulate the emitted SH power by about one order of magnitude. The devised hybrid platforms are therefore appealing in view of enabling the electrical control of flat nonlinear optical devices.

Metamaterials, as artificially structured materials composed of subwavelength arrays of resonant unit cells, can exhibit exotic properties beyond those accessible to natural materials. They were initially proposed for challenging fundamental laws and demonstrating negative refraction in the microwave regime, and subsequently exploited as a versatile platform to manipulate electromagnetic waves throughout the spectrum via their extreme scalability. Over the past decade, research into metamaterials has been extended to a search for real-world applications, leading to the concept of metadevices, defined as metamaterial-based devices that can operate in an active manner. Due to their subwavelength scale, metamaterials present intriguing strategies for active tuning and provide flat, high-efficiency alternatives to conventional optical systems based on bulky components. In this topical review, we summarize the development of active metamaterials and metadevices ranging from microwave to visible wavelengths, including milestones as well as the state of the art. We survey tuning strategies based on mechanical reconfiguration and incorporation with active materials such as varactor diodes, semiconductors, liquid crystals, phase change materials, superconductors, and two-dimensional materials under various external stimuli, and discuss their fascinating advantages and potential challenges to be confronted. Finally, future prospects together with several emerging tuning strategies and materials are presented at the end. [ABSTRACT FROM AUTHOR]

The Stokes polarimeter based on liquid crystal variable retarders (LCVRs) is envisaged as a promising novel technique for polarization measurement in space applications due to the inherent advantage of eliminating the need for conventional rotating polarizing optics and increasing the measuring speed. However, the intrinsic multi-beam interference in LCVRs limits its polarization accuracy by several percent. How to eliminate the influence of the interference effect becomes an urgent issue for the liquid-crystal-based Stokes polarimeter. The present study introduces a simplified but effective interference model based on the thin-film optics and polarized light theory to simulate the relationship between the interference effect of the LCVRs-based Stokes polarimeter and the polarization accuracy. The simulation results show that the transmittance variation of LCVR with the derived voltage is caused by multi beam interference between the indium tin oxide (ITO) film and the liquid crystal within LCVR, which produces a few percent of instrumental polarization. The instrumental polarization is about 0.01 and different for different wavelengths. An optimization method was proposed to reduce the instrumental polarization to 0.002, effectively improving the polarization sensitivity of the Stokes polarimeter limited by the interference. In addition, an experimental setup was built up to measure and analyze the influence of the interference effect of the LCVRs-based Stokes polarimeter on the polarization accuracy before and after the optimization. The experiment results are in good agreement with the simulation. [ABSTRACT FROM AUTHOR]

Humankind has been obsessed with knots in religion, culture and daily life for millennia, while physicists like Gauss, Kelvin and Maxwell already involved them in models centuries ago. Nowadays, colloidal particles can be fabricated to have shapes of knots and links with arbitrary complexity. In liquid crystals, closed loops of singular vortex lines can be knotted by using colloidal particles and laser tweezers, as well as by confining nematic fluids into micrometer-sized droplets with complex topology. Knotted and linked colloidal particles induce knots and links of singular defects, which can be interlinked (or not) with colloidal particle knots, revealing the diversity of interactions between topologies of knotted fields and topologically nontrivial surfaces of colloidal objects. Even more diverse knotted structures emerge in nonsingular molecular alignment and magnetization fields in liquid crystals and colloidal ferromagnets. The topological solitons include hopfions, skyrmions, heliknotons, torons and other spatially localized continuous structures, which are classified based on homotopy theory, characterized by integer-valued topological invariants and often contain knotted or linked preimages, nonsingular regions of space corresponding to single points of the order parameter space. A zoo of topological solitons in liquid crystals, colloids and ferromagnets promises new breeds of information displays and a plethora of data storage, electro-optic and photonic applications. Their particle-like collective dynamics echoes coherent motions in active matter, ranging from crowds of people to schools of fish. This review discusses the state of the art in the field, as well as highlights recent developments and open questions in physics of knotted soft matter. We systematically overview knotted field configurations, the allowed transformations between them, their physical stability and how one can use one form of knotted fields to model, create and imprint other forms. The large variety of symmetries accessible to liquid crystals and colloids offer insights into stability, transformation and emergent dynamics of fully nonsingular and singular knotted fields of fundamental and applied importance. The common thread of this review is the ability to experimentally visualize these knots in real space. The review concludes with a discussion of how the studies of knots in liquid crystals and colloids can offer insights into topologically related structures in other branches of physics, with answers to many open questions, as well as how these experimentally observable knots hold a strong potential for providing new inspirations to the mathematical knot theory. [ABSTRACT FROM AUTHOR]

This paper investigates nematic liquid crystals in three-dimensional curved space, and determines which director deformation modes are compatible with each possible type of non-Euclidean geometry. Previous work by Sethna et al showed that double twist is frustrated in flat space , but can fit perfectly in the hypersphere. Here, we extend that work to all four deformation modes (splay, twist, bend, and biaxial splay) and all eight Thurston geometries. Each pure mode of director deformation can fill space perfectly, for at least one type of geometry. This analysis shows the ideal structure of each deformation mode in curved space, which is frustrated by the requirements of flat space. [ABSTRACT FROM AUTHOR]

We developed a microdisplay-based microscope projection photolithography (MDMPP) technique in which a liquid crystal (LC) microdisplay is used as a reconfigurable photomask for a microscope projector. The LC microdisplay provides a significant advantage in terms of cost and speed since patterns can be generated through software instead of redesigning and fabricating glass photomasks. The constructed MDMPP system could produce line patterns as narrow as 2.4 µm, smaller than that specified by the diffraction limit, with the aid of a 4× objective lens. The achievement of a linewidth smaller than the theoretical limit may be ascribed to a combination of overexposure and the underetching effect, in addition to the good optical performance of the system. In a diffraction experiment performed with fabricated slits, the application of the MDMPP technique helped provide various patterns of the slits, demonstrating the potential usefulness of the MDMPP system in undergraduate optics courses. We expect that MDMPP can contribute to the field of physics education and various areas of research, such as chemistry and biology, in the future. [ABSTRACT FROM AUTHOR]

The positioning accuracy of machine-tool tables used for translatory movement and coordinate measuring machine carriages requires improvement. Transmission and blocking of light can be realized by combining a transmissive liquid crystal and a polarizing plate. In this study, this technique was applied to a laser interferometer to realize selective multi-degree-of-freedom motion measurement using one measurement system. A ball lens was adopted as a reflecting mirror, and the rotational-movement amount was measured using a photodetector. In addition, rotational movement with two degrees of freedom was selectively measured using one interferometer, through transmission and blocking of light. It was found that the pitch and yaw rotational movement can be selectively measured using the difference between displacements of the axial directions of two ball lenses for the movement of the goniometer stage with 0.0032° resolution and the rotational stage with 0.004° resolution, respectively, and that the influence of the crosstalk of yaw and pitch is slight when the pitch and yaw rotational movements are simultaneously applied to the stage. Therefore, there is scope for this technique to be used to improve multi-degree-of-freedom motion measurements. [ABSTRACT FROM AUTHOR]

A novel liquid crystal (LC)-based holographic antenna (HA) with low sidelobe level is proposed in this paper to achieve large beam scanning range and multi-beam scanning property. The operating principle and the design procedure of the LC HA are presented. The influence of the on-to-off ratio of the holographic array element on the reconfigurable HA's radiation characteristics is investigated. It is shown that the larger on-to-off ratio can reduce the sidelobe level of the reconfigurable HA, or decrease the iteration number of sidelobe optimization algorithms and enable the algorithms to converge to a much lower optimal sidelobe level. An effective design method to increase the array element's on-to-off ratio is proposed through introducing an auxiliary radiation component, which offsets the radiation for the turn off state and enhances the radiation for the turn on state. A prototype of the LC HA consisting of the elements with large on-to-off ratio is designed and simulated to demonstrate the design method and theoretical predictions. Results show that, benefiting from the enhanced on-to-off ratio, the LC HA naturally presents a sidelobe level of −12.2 dB at broadside without any optimization. Compared with previous work, the sidelobe level is 3.2 dB lower than the case without large on-to-off ratio. Moreover, the proposed LC HA shows a quite large beam scanning range rising from −57.7° to +57.4° and a dynamic multi-beam property. [ABSTRACT FROM AUTHOR]

We present a compact tunable Fabry–Pérot filter operating at mid-infrared wavelengths (3–5 µm) with novel actuators based on liquid crystal elastomers (LCEs). These are a new class of shape-memory materials with potential for achieving large reversible actuation based on different external stimuli. For actuating the Fabry–Pérot filter, microheaters and thermo-actuated LCE layers were fabricated as spacers between two Bragg mirrors allowing a controlled change of the air-filled resonator. The ability to integrate LCEs with standard microfabrication techniques was thus demonstrated. The full-width at half maximum of the filter transmission peak is 143 nm at 4.58 µm. A tuning range of 260 nm in the second interference order is realized by applying a maximum voltage of 7.3 V. [ABSTRACT FROM AUTHOR]

Display technology with ultrafine pixels for near-eye application is a rapidly growing field due to the recent emergence of augmented/mixed reality. With the constant demand for high energy efficiency, long lifetime, and high luminosity, micro-LED displays based on compound semiconductors are promising candidates for such applications. However, miniaturizing LEDs results in significant drawbacks in terms of their quantum efficiency, current injection efficiency, and heat extraction. With relatively low device resistance compared to that of liquid crystals or organic LEDs, micro-LEDs are also more susceptible to the effects of parasitic resistance. In this study, gallium nitride based micro-LED displays with very small pixels (5 μm pixel, 10 μm pitch) are fabricated to study the thermal–electrical effect of meshed hybrid conductors on the optical emission efficiency. In situ thermographic imaging with I–V measurement confirms a significant trade-off among heat transfer, electrical conductivity, and light extraction efficiency. An increase of 37.9% in the emission efficiency (2540 pixels per inch, 5 μm pixels, 1 mm2 display, at 49.2 °C) is achieved by optimizing the thermal and electrical conduction paths. This study experimentally confirms the importance of thermal management and multi-physics analysis in designing ultra-small-pixel micro-LEDs with high energy efficiency. [ABSTRACT FROM AUTHOR]

The Advanced Space-based Solar Observatory (ASO-S) is a mission proposed by the Chinese Solar Physics Community. As one of the three payloads of ASO-S, the Full-disc Magneto-Graph (FMG) will measure the photospheric magnetic fields of the entire solar disk with high spatial and temporal resolution, and high magnetic sensitivity, where liquid crystal variable retarder (LCVR) is the key to whether FMG can achieve its scientific goal. So far, there is no space flight experience for LCVR. Therefore, irradiation study for LCVRs becomes more important and urgent in order to make sure their safety and reliability in space application. In this paper, λ irradiation, proton irradiation, and ultra-violet (UV) irradiation are tested for LCVRs respectively. The optical and chemical properties during irradiation tests are measured and analyzed. For optical properties, there is no significant change in those parameters FMG payload concerned except the retardation. Although there is no drastic degradation in the retardation versus voltage during irradiations, the amount of retardation variation is much higher than the instrument requirements. Thus, an in-flight retardation versus voltage should be added in FMG payload, reducing or even avoiding the impact of retardation change. For chemical properties, the clearing point and birefringence of the LC materials almost have no change; the ion density dose not change below 60 krad[Si], but begin to increase dramatically above 60 krad[Si]. [ABSTRACT FROM AUTHOR]

In the paper, we study the effect of an applied magnetic field on nematic liquid crystals such as magnetic field-induced instability in anisotropic liquid crystals. Under a planar field ansatz for the liquid crystal, the time-dependent system of anisotropic liquid crystals for the Oseen–Frank model reduces to a quasilinear parabolic equation for the orientation angle of the liquid crystal involving critical nonlinearity due to elastic anisotropy. We first establish the global existence of weak solutions to the parabolic problem. When the unequal elastic constants are sufficiently close, we prove convergence to an equilibrium of global smooth solutions, and examine the dynamical instability of an aligned state induced by a strong magnetic field. [ABSTRACT FROM AUTHOR]

We consider an electromagnetic field propagating within a cylindrical waveguide whose core consists of a material in which the elongated molecules have the tendency to rotate helically along all directions perpendicular to a given vector which we chose to be along the axis of the fiber. This type of structure can be found in some chiral nematic materials such as blue phases. We establish the electromagnetic equations governing the dynamics of all the orders of propagating modes and solve them numerically. We found the band structure of the mentioned modes and show that they can be classified in quasi-transverse magnetic and electric modes whose corresponding cut-off frequencies are in some cases degenerated. Also, the profile field amplitudes versus the radial axis of the fiber are depicted and analyzed. Finally, we discuss how the modes are conformed and their conditions to propagate electromagnetic waves. [ABSTRACT FROM AUTHOR]

Recently, physical fields with topological configurations are evoking increasing attention due to their fascinating structures both in fundamental researches and practical applications. Therein, topological light fields, because of their unique opportunity of combining experimental and analytical studies, are attracting more interest. Here, based on the Pancharatnam–Berry (PB) phase, we report the creation of Hopf linked and Trefoil knotted optical vortices by using phase-only encoded liquid crystal (LC) holographic plates. Utilizing scanning measurement and the digital holographic interference method, we accurately locate the vortex singularities and map these topological nodal lines in three-dimensions. Compared with the common methods realized by the spatial light modulator (SLM), the phase-only LC plate is more efficient. Meanwhile, the smaller pixel size of the LC element reduces the imperfection induced by optical misalignment and pixellation. Moreover, we analyze the influence of the incident beam size on the topological configuration. [ABSTRACT FROM AUTHOR]

Many biological systems, such as bacterial suspensions and actomyosin networks, form polar liquid crystals. These systems are 'active' or far-from-equilibrium, due to local forcing of the solvent by the constituent particles. In many cases the source of activity is chiral; since forcing is internally generated, some sort of 'torque dipole' is then present locally. But it is not obvious how 'torque dipoles' should be encoded in the hydrodynamic equations that describe the system at the continuum level: different authors have arrived at contradictory conclusions on this issue. In this work, we resolve the paradox by presenting a careful derivation, from linear irreversible thermodynamics, of the general equations of motion of a single-component chiral active fluid with spin degrees of freedom. We find that there is no unique hydrodynamic description for such a fluid in the presence of torque dipoles of a given strength. Instead, at least three different hydrodynamic descriptions emerge, depending on whether we decompose each torque dipole as two point torques, two force pairs, or one point torque and one force pair—where point torques create internal angular momenta of the chiral bodies (spin), whereas force pairs impart centre of mass motion that contributes to fluid velocity. By considering a general expansion of the Onsager coefficients, we also derive a new shear-elongation parameter and cross-coupling viscosity, which can lead to unpredicted phenomena even in passive polar liquid crystals. Finally, elimination of the angular variables gives an effective polar hydrodynamics with renormalized active stresses, viscosities and kinetic coefficients. Remarkably, this can include a direct contribution of chiral activity to the equation of motion for the polar order parameter, which survives even in 'dry' active systems where the fluid velocity is set to zero. [ABSTRACT FROM AUTHOR]

We give a description of the intrinsic geometry of elastic distortions in three-dimensional nematic liquid crystals and establish necessary and sufficient conditions for a set of functions to represent these distortions by describing how they couple to the curvature tensor. We demonstrate that, in contrast to the situation in two dimensions, the first-order gradients of the director alone are not sufficient for full reconstruction of the director field from its intrinsic geometry: it is necessary to provide additional information about the second-order director gradients. We describe several different methods by which the director field may be reconstructed from its intrinsic geometry. Finally, we discuss the coupling between individual distortions and curvature from the perspective of Lie algebras and groups and describe homogeneous spaces on which pure modes of distortion can be realised.

We investigate the effects of extrinsic curvature on the turbulent behavior of a 2D active nematic confined to the surface of a cylinder. The surface of a cylinder has no intrinsic curvature and only extrinsic curvature. A nematic field reacts to the extrinsic curvature by trying to align with the lowest principle curvature, in this case parallel to the long axis of the cylinder. When nematics are sufficiently active, there is a proliferation of defects arising from a bend or splay instability depending on the nature of the active stress. The extrinsic curvature of the cylinder breaks the rotational symmetry of this process, implying that defects are created parallel or perpendicular to the cylinder depending on whether the active nematic is contractile or extensile.

Weinvestigate the dynamic assembly and swarm translocation of anisometric colloidal particles dispersed in a nematic liquid crystal and driven above a photosensitive surface.Weuse liquid crystalenabled electrophoresis to propel these particles via an alternating electric field perpendicular to the sample cell. By manipulating the anchoring conditions on one surface of the experimental cell, we obtain a spatially extended spiral pattern of the liquid crystal orientation that induces the dynamic assembly of a rotating colloidal mill. This structure can be transported by translocating the topological defect above the photosensitive surface.Wecomplement our findings with a theoretical model that captures the basic physics of the process, by formulating an analytic equation for the director field above the surface. Our reconfigurable nematic assemblies may be used as a test bed for complex swarming behaviour in biological and artificial microscale systems. [ABSTRACT FROM AUTHOR]

Phase transitions in soft matter systems reveal some of the interesting structural phenomena at the levels of individual entities constituting those systems. The relevant energy scales in soft matter systems are comparable to thermal energy ( k _B T ∼ 10 ^−21 J). This permits one to observe interesting structural dynamics even at ambient conditions. However, at the nanoscale most experimental probes currently being used to study these systems have been either plagued by low sensitivity or are invasive at molecular scales. Nitrogen-vacancy (NV) centers in diamond is emerging as a robust quantum probe for precision metrology of physical quantities (e.g. magnetic field, electric field, temperature, and stress). Here, we demonstrate by using NV sensors to probe spin-fluctuations and temperature simultaneously to obtain information about controlled phase changes in a soft matter material as a function of temperature. The soft matter system chosen for the study is a standard liquid crystalline (LC) material which shows distinct phases close to room temperature. Individual NV centers at depths of a few nm are used as a probe to detect magnetic signals emanating from a few molecular layers of sample on the surface of the diamond. The organization and collective dynamics of LC molecules in nanoscopic volumes are discussed. Our study aims to extend the areas of application of quantum sensing using NV centers to probe the soft matter systems, particularly those exhibiting mesophases and interesting interfacial properties.

Many biological systems, such as bacterial suspensions and actomyosin networks, form polar liquid crystals. These systems are ‘active’ or far-from-equilibrium, due to local forcing of the solvent by the constituent particles. In many cases the source of activity is chiral; since forcing is internally generated, some sort of ‘torque dipole’ is then present locally. But it is not obvious how ‘torque dipoles’ should be encoded in the hydrodynamic equations that describe the system at the continuum level: different authors have arrived at contradictory conclusions on this issue. In this work, we resolve the paradox by presenting a careful derivation, from linear irreversible thermodynamics, of the general equations of motion of a single-component chiral active fluid with spin degrees of freedom. We find that there is no unique hydrodynamic description for such a fluid in the presence of torque dipoles of a given strength. Instead, at least three different hydrodynamic descriptions emerge, depending on whether we decompose each torque dipole as two point torques, two force pairs, or one point torque and one force pair—where point torques create internal angular momenta of the chiral bodies (spin), whereas force pairs impart centre of mass motion that contributes to fluid velocity. By considering a general expansion of the Onsager coefficients, we also derive a new shear-elongation parameter and cross-coupling viscosity, which can lead to unpredicted phenomena even in passive polar liquid crystals. Finally, elimination of the angular variables gives an effective polar hydrodynamics with renormalized active stresses, viscosities and kinetic coefficients. Remarkably, this can include a direct contribution of chiral activity to the equation of motion for the polar order parameter, which survives even in ‘dry’ active systems where the fluid velocity is set to zero.

We investigate the dynamic assembly and swarm translocation of anisometric colloidal particles dispersed in a nematic liquid crystal and driven above a photosensitive surface. We use liquid crystal-enabled electrophoresis to propel these particles via an alternating electric field perpendicular to the sample cell. By manipulating the anchoring conditions on one surface of the experimental cell, we obtain a spatially extended spiral pattern of the liquid crystal orientation that induces the dynamic assembly of a rotating colloidal mill. This structure can be transported by translocating the topological defect above the photosensitive surface. We complement our findings with a theoretical model that captures the basic physics of the process, by formulating an analytic equation for the director field above the surface. Our reconfigurable nematic assemblies may be used as a test bed for complex swarming behaviour in biological and artificial microscale systems.

Topological insulators are materials that conduct on the surface and insulate in their interior due to non-trivial topology of the band structure. The edge states on the interface between topological (non-trivial) and conventional (trivial) insulators are topologically protected from scattering due to structural defects and disorders. Recently, it was shown that photonic crystals (PCs) can serve as a platform for realizing a scatter-free propagation of light waves. In conventional PCs, imperfections, structural disorders, and surface roughness lead to significant losses. The breakthrough in overcoming these problems is likely to come from the synergy of the topological PCs and silicon-based photonics technology that enables high integration density, lossless propagation, and immunity to fabrication imperfections. For many applications, reconfigurability and capability to control the propagation of these non-trivial photonic edge states is essential. One way to facilitate such dynamic control is to use liquid crystals (LCs), which allow to modify the refractive index with external electric field. Here, we demonstrate dynamic control of topological edge states by modifying the refractive index of a LC background medium. Background index is changed depending on the orientation of a LC, while preserving the topology of the system. This results in a change of the spectral position of the photonic bandgap and the topological edge states. The proposed concept might be implemented using conventional semiconductor technology, and can be used for robust energy transport in integrated photonic devices, all-optical circuity, and optical communication systems.

Observations of the daytime sky polarization are useful calibration tools for large-aperture telescopes, as well as a testbed for polarized radiative transfer models. We present an instrument capable of measuring the complete full-sky Stokes vector over visible/NIR broad bands. The design utilizes liquid crystal variable retarders and a dual-beam polarization analyzer, allowing for a clear and cloudy sky acquisition cadence near 12 s which shows minimal image artifacts from solar and cloud motion. In this article, we detail the design, full-field calibration methodology, and Haleakala observations, which provide an absolute polarimetric accuracy on individual Stokes parameters of better than 3% across VRI bandpasses. Angle and degree of polarization images are compared with a single-scattering model and the more complete MODTRAN-4P polarized radiative transfer package. Comparisons with independent measurements atop nearby Mauna Loa show similar polarization structure, but results suggest a relatively larger depolarization from surface reflections beneath Haleakalā. [ABSTRACT FROM AUTHOR]

Using tools and concepts from contact topology we show that non-vanishing twist implies conservation of the layer structure in cholesteric liquid crystals. This leads to a number of additional topological invariants for cholesteric configurations, such as layer numbers, that are not captured by traditional descriptions, characterises the nature and size of the chiral energy barriers between metastable configurations, and gives a geometric characterisation of cholesteric dynamics in any context, including active systems, those in confined geometries or under the influence of an external field.

A sensitive electrochemical sensor based on carbon paste and inclusion of ionic liquid crystal [(1-Butyl-1-methylpiperidinium hexafluorophosphate)] in presence of sodium dodecyl sulfate (ILCMCPE.....SDS) for the electrochemical determination of Enoxacin (EN) was prepared. Different ionic liquids were used and compared, namely (1-n-Hexyl-3-methyl imidazolium tetrafluoroborate) (ILMCPE1.....SDS) and (1-Butyl-4-methyl pyridinium tetrafluoroborate) (ILMCPE2.....SDS). The studied ionic liquids mimic cell membranes for their interaction with drug intake through cell membranes. We found that ILCMCPE.....SDS exhibited good electrochemical performances with higher conductivity and lower electron transfer resistance due to the combining effect of high ion conductivity, sensitivity, fast electron transfer, stability and antifouling ability of the ionic liquid crystal. SDS enhanced the preconcentration/accumulation of EN species in the ionic form at the surface. Excellent performance of ILCMCPE.....SDS for the determination of EN in the linear dynamic range of 6.67 10-7 to 2.22 10-5 mol L-1 with a correlation coefficient 0.9998 and LOD 3.28 10-9 mol L-1. Simultaneous determination of binary mixtures dopamine/enoxacin and epinephrine/enoxacin was demonstrated with good peak potentials separations. This method was successfully applied for direct determination of EN in human urine samples with good recovery results. The ILCMCPE.....SDS showed also high reproducibility selectivity and anti -interference ability. [ABSTRACT FROM AUTHOR]