This PDF file contains the front matter associated with SPIE Proceedings Volume 13121, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Nematic liquid crystals exhibit nanosecond electro-optic response to an applied electric field which modifies the degree of orientational order without realigning the molecular orientation. However, this nanosecond electrically-modified order parameter (NEMOP) effect requires high driving fields, on the order of 10⁸ V/m for a modest birefringence change of 0.01. In this work, we demonstrate that a nematic phase of the recently discovered ferroelectric nematic materials exhibits a robust and fast electro-optic response. Namely, a relatively weak field of 2 × 10⁷ V/m changes the birefringence by ≈ 0.04 with field-on and -off times around 1 μs. This microsecond electrically modified order parameter (MEMOP) effect shows a greatly improved figure of merit when compared to other electro-optical switching modes in liquid crystals, including the conventional Frederiks effect, and has a potential for applications in fast electro-optical devices such as phase modulators, optical shutters, displays, and beam steerers.

A review of recent advances in molecular assembly of liquid crystalline chiral photonic crystals is presented, particularly on fabrication of extraordinarily thick [>2 mm] cholesteric liquid crystals (CLC), and large-areal size monocrystalline Blue-phase liquid crystals (BPLC). CLC’s as 1-D chiral photonic crystals possess large ultrafast optical nonlinearity suitable for self-compression, polarization switching and modulation of complex vector beams. These super thick and highly nonlinear CLC’s are estimated to be capable of all optical switching [π- phase shift] at sub-picosecond (~0.1 x 10^-12 s) speed with low threshold energy fluence of ~ 0.25 μJ/cm². Large areal size monocrystalline BPLC’s will preserve the phase front uniformity in free-space image processing and yield better efficiency, resolution, and image/signal qualities than their typical polycrystalline counterparts.

Photoalignment is one the important techniques to fabricate flat panel displays, birefringent functional films, and polarized optical diffraction devises. Thinner optical devises are attained when the optical film exhibits high birefringence. We investigated systematic studies on photoalignable liquid crystalline polymers (PLCPs), which achieve molecularly oriented structure for themselves, showing the bulk-photoalignment. This paper describes new PLCPs which reveal high photosensitivity, high photoalignability, and controllability of generated birefringence by means of in situ modification of the oriented mesogenic side groups. The initial generated birefringence of the PLCP films is 0.15, whereas the improved birefringence exceeds 0.4 is achieved via in situ modification of the oriented mesogenic side groups. Using PLCP films, polarization gratings are fabricated.

Liquid Crystals are extraordinary materials for the organization of fluids and nanoparticles. The director field wraps around colloidal inclusions and inevitably forms topological defects to meet far-field boundary conditions. Droplets of isotropic fluids which promote planar anchoring form boojums in the surrounding LC which cause bulk quadrupolar distortions. At an air-LC interface the droplets directly contact the air and one boojum can disappear leaving a solitary boojum pointing down. As the liquid crystal layer becomes thinner, the hybrid anchoring of the LC layer causes the boojum to tilt enabling the formation of dipolar chains. As the layer becomes thinner still, the bottom planar alignment forces the second boojum to reappear recovering the quadrupolar alignment. The elastocapillary force associated with droplets at an air-LC interface is a surprising many body force which can distort the layer thickness by up to 1 micron leading to the formation of rounded superstructures containing thousands of droplets. Polydisperse droplets can enable the formation of branched structures where a mix of dipolar and quadrupolar interaction allows for the formation of y-branches. The self-assembly properties of LC enable the formation of interesting emulsions and switchable hybrid materials.

Topological defects in liquid crystal diffract light, scatter light, and switch the photon angular momentum. Electric field can switch the defects on and off, since the liquid crystal is fluid and highly operatable. When the combination and the arrangement satisfy the topological conservation laws, the defects assemble into ordered structure by themselves. The new order is topologically protected, self-retained, and self-healing. Our research focus on the rules of the right combination, and if the topological defects drive the formation of natural patterns and optical texture. In the first part of this talk, a new model for 2D defect array is demonstrated. The model has been under construction based on our experimental results. Topological defects are arranged in rectangular, triangular, square, pentagonal, and hexagonal lattices like atoms in crystals and quasicrystals. By solving the Euler-Lagrange equation of the director field of a unit cell and by integrating the topological rules into the boundary conditions, the director field of a defect crystal are easily obtained. A large variety of topological defect crystals and quasicrystals are derived. The defects are radial or vortex-like. Both nematic and vector orders are considered. The second part of the talk is about the generation of topological defect arrays. The pads, crossed-strips, and pores on the electrode grab the defects to put them in order. Unexpectedly, the pore generates a pair of radial (+1) and hyperbolic (-1) defects, just in analogy to electric dipoles. The dipoles spontaneously align in parallel order, forming domains. In unit cells smaller than 10 um x 10 um, the defect dipoles still align in a large range, without relying on lithography and surface treatment. The spontaneous dipole aliment breaks through the technical limit. Following the natural self-assembly of topological defects, photonic crystals or artificial tissues simply grow and form.

Laser ultrasonics using a photorefractive liquid crystal was investigated in both coaxial and counter-optical setups. The proposed laser-ultrasonic method involves irradiating an object with a laser pulse to produce an ultrasonic vibration and then using another laser beam to detect the vibration. The phase of the laser beam reflected from the object is shifted by the ultrasonic vibration. By using liquid crystals with photorefractive properties, this phase shift can be detected. Compared to traditional laser ultrasonic methods, this system offers a simpler optical setup and provides more accurate measurements that are unaffected by environmental vibrations.

We have constructed a near-infrared hyperspectral S₃ imager consisting of a circularly polarized broadband light source, a liquid crystal polarization grating, and a commercial hyperspectral camera. The circular polarization diffraction efficiency of the polarization grating was over 99 percent at 1550 nm. This imager is capable of obtaining both hyperspectral circular polarization distributions and conventional hyperspectral images. Using the S₃ hyperspectral imager, we demonstrated the classification of plastic samples with a deep learning algorithm, which can be applied to waste classification in recycling plants.

We tried to develop the liquid crystal geometric phase elements (LCGPE) that are available for use in the midand far-infrared (MIR and FIR) wavelengths. In view of optical throughput, the materials for making GPE were selected by the use of a Fourier-transform infrared spectrometer. The LC polarization grating (LCPG) and LC q-plate (LCQP) designed for 3.85 µm and 9.5,µm are respectively fabricated, and evaluated their diffraction properties experimentally.

Overview is presented on using liquid crystals in single-photon sources (SPSs) exhibiting antibunching (separation of all photons in time) with definite linear or circular polarizations. SPSs are key components for secure, long-distance quantum communication systems with quantum repeaters. If we can produce a photon with definite polarization, the efficiency of the quantum cryptography system is doubled. Both nematic and cholesteric liquid crystal (CLC) hosts were used to create definite linear or circular polarization of antibunched photons emitted by different types of single emitters (dye molecules, colloidal semiconductor nanocrystal quantum dots (NQDs) with different fluorescence wavelengths, nitrogen-vacancy (NV) color-center nanodiamonds). Definite polarization from nanocrystals doped with trivalent rare-earth ions in liquid crystal hosts at low light level is also reported. Both monomeric and glassy oligomeric liquid crystal hosts have been used. Raman scattering in monomeric liquid crystals can prevent photon antibunching at some fluorescence wavelengths. A circular polarized microcavity resonance in NQD fluorescence in a 1-D photonic bandgap CLC microcavity and spontaneous emission enhancement as well as some pitfalls on purity of single-photon emission with using photoalignment materials are discussed (photoalignment materials’ fluorescence imaging may show single-emitter fluorescence behavior with emission of antibunched light).

The impact of molecular core chirality on helical columnar molecular assemblies has been investigated for enantiopure octahedral metallomesogens with propeller-shaped ΔΔ chirality. Although the inner stacking structures in helical columnar liquid crystals (Helical Col LCs) strongly affect the resultant functional properties such as ferroelectricity, there have been no definitive reported method to determine the inner structure. In this work, we used a combination of grazing-incidence (GI) X-ray diffraction spectroscopy and molecular dynamics (MD) simulations to reveal that the chiral octahedral metallomesogens stack with both the position and C₃ axis rotating along the columnar axis. Therefore, the structure was classified as a hybrid of two proposed major helical stacking types; however, the detailed stacking structure of each type has not been sufficiently understood. Further structural analyses of the simulated structures highlight the interplay of the steric repulsion between the ΔΔ chiral cores, π-stacking, and dipolar interactions in the helical formation. The accommodation of such weak interactions was confirmed for enantiopure samples by vibrational circular dichroism and UV-Vis spectroscopic studies, whereas racemic compounds were found to receive stronger intermolecular interactions to pack tightly.

Influence of surface pre-tilt setting on dynamic initial driving torque of an SSD (Smectic Single Domain) liquid crystal drive mode has been investigated. Unlike typical nematic liquid crystal drive mode, a smectic liquid crystal drive mode has some significant influence by its smectic layer switching behavior. To clarify the layer switching influence, an initial driving torque was investigated how the initial torque was formed, how the torque interacted to the dynamic layer distortion behavior, and so on. Empirical approaches included both dielectric relaxation behavior and dynamic retardation switching behavior. These measurements suggested that the initial surface pre-tilt setting was one of the primary influential factors to govern dynamic optical response profile of an SSD-LC panel.

Planar liquid-crystal-polymer (LCP) optical elements are increasingly being used to enable novel astronomical observational modes. These optical elements include diffractive waveplates for spectropolarimetry, optical vortex phase masks for high-contrast stellar coronagraphy, pupil-plane phase masks for both beam shaping and nulling interferometry, and Zernicke phase masks for wavefront sensing. Several of these devices have already been used on ground-based telescopes, and further development may ultimately enable these techniques to be used to detect and measure spectra of Earth-like exoplanets around nearby stars.

Plasma mirrors are nonlinear optical components that, in their “off” state, have low reflectivity and high transmission. A high-intensity laser pulse will excite a plasma on the component surface triggering the “on”, high reflectivity state. Plasma mirrors are used to dynamically remove laser pre-pulse from ultrashort, ultrahigh intensity laser pulses, greatly increasing temporal pulse contrast. We have shown that free standing, ultrathin (<30 nm) films of the liquid crystal 8CB can serve as excellent, renewable plasma mirrors that can support pulses at powers up to 1 PW. The 8CB films have low vapor pressure and can be formed at high repetition rate inside a vacuum chamber at relatively low cost. More than conventional plasma mirrors using standard optical substrates, ultrathin films can facilitate versatile beam geometries for experiments via dynamic beam redirection. We have also introduced new computational models using both particle-in-cell simulations and empirical models. In this work, we describe both how free standing, ultrathin liquid crystal films can serve as excellent plasma mirrors and consider pathways to multi-PW operation, including use of liquid crystal mixtures.

Liquid crystal microparticles controlled their molecular orientation exhibit unique material properties such as responsiveness to external stimuli. These material properties can be enhanced by introduction of crosslinked structure. Recently, we achieved the fabrication of the chiral nematic liquid crystalline polymer microparticles by dispersion polymerization. The particles are monodisperse and have controlled molecular orientation, thus potentially paving the way for the numerous applications. In this study, we investigated the material properties of the chiral nematic liquid crystalline polymer particles. As a result, the obtained polymer particles showed the wavelength-dependent light reflection based on the helical molecular orientation of the chiral nematic liquid crystalline polymer. In addition, we demonstrated introduction of a crosslinked structure into polymer particles and investigated its effect on the material properties of the microparticles. As a result, the introduction of crosslinked structure gave the particles the solvent resistance without losing other material properties.

A solid-state steerable camera developed to generate high-resolution color images is presented. The camera can deliver greater than 16 MP resolution over a given field of view at a lower cost, in comparison to conventional camera systems. The camera incorporated a Liquid Crystal Polarized Grating (LCPG) structure, enabling imaging over an 87-degree field of view (FOV). The instantaneous field of view (iFOV) is approximately 10.4 degrees with a focal length of 17 mm, captured by a 2.1 MP sensor. The combined instantaneous fields of view generated by the eight independent steering directions cover the entire FOV. Images captured in ambient light via the LCPG imaging system suffer from chromatic dispersion due to the nature of the diffraction gratings. A narrow bandpass filter centered around 600 nm, is introduced to reduce the chromatic dispersion. A unique image processing neural network is used to correct residual spherochromatism generated by the LCPG device on a per iFOV basis. The entire system, encompassing the LCPG, voltage driver, optics, spectral filters, polarization filters, sensor, and neural network image processing program, has been used successfully in diverse operating conditions. The results show the viability of the steerable solid-state camera concept, highlighting its potential for high-resolution imaging with enhanced cost efficiency and reduced processing loads.

Smart windows are active windows that can adjust transmittance and can perform functions such as energy saving, indoor illumination control in conjunction with smart lighting or daylighting, user privacy protection, and active space separation. Smart window technology has high potential to expand not only to buildings but also to next-generation mobility fields such as electric vehicles and air taxis. Types of smart windows include electrochromic type(EC), polarized particle type(PP), and liquid crystal type(LC). In the case of liquid crystal systems, polymer dispersed liquid crystal systems (PDLC) are being developed the most. However, the PDLC has the advantage of fast response speed, but has the disadvantage of high driving voltage and difficulty in realizing color. In this study, we developed a liquid crystal-based smart window capable of low-power operation and color implementation that can be combined with building-integrated solar power to save energy in buildings. In order to realize color, dyes were developed in a way that did not affect the liquid crystal. And in order to apply it to building windows, we developed a liquid crystal smart window that can operate without a polarizer for arrangement of liquid crystals, which is different from the existing liquid crystal method by considering transmittance. As a result of measuring the color, operating voltage, and current of the liquid crystal smart window, the CIE-LAB index difference for color was 20.86 (L: 41.33 → 34.23, a: - 10.43 → -3.25, b: -9.88 → -3.3), The voltage was 5V and the current was 4.14X10-7[A]. In addition, the driving voltage and current result was 2.07uW, confirming that low-power driving was possible.

Optical vortex generation has attracted great interest in the scientific community due to its broad applicability in various technological developments. Several studies on optical vortex generation have been performed in liquid crystal media, specifically in transmission liquid crystal light valves; controlled and localized induction by light of optical vortex has been experimentally observed. An adequate amplitude equation, derived from first principles, describes this phenomenon. Theoretically, we find different localized vortex solutions depending on the bifurcation parameter. Experimentally, we analyze the transition point concerning voltage and intensity, proposing further investigation into these vortex-like solutions and their detailed characterization of structural transitions. The theoretical model of the liquid crystal light valve predicts several vortex structures that have not been studied experimentally. Based on a liquid crystal light valve experiment with applied light and voltage, we show the transition and appearance of different vortex structures. The study and detailed characterization of structures outside the limits predicted by the theory and possible corrections are proposed.

Liquid crystal networks (LCNs) have been extensively researched due to their unique ability to change shape in response to external stimuli, such as light or heat, through anisotropic expansion resulting from the arrangement of liquid crystal molecules. Traditionally, microstructures are polymerized from the surface of the substrate, limiting their ability to achieve shrinking deformation at the microscale. This paper proposes using two-photon polymerization to fabricate shrinking micro-pillars supported by an LCN wall, avoiding restrictions from the substrate surface. In this study, the fabricated LCN pillars with lengths of 30 microns and thicknesses of 5.5, 8.5, and 11.5 microns achieved a maximum shrinking ratio of 17.33%.

Bistable coupled systems can exhibit nonlinear waves. Domino waves represent a straightforward example of nonlinear waves in everyday life. Domino waves are observed in extended bistable chains where a domino has two stable equilibria: vertical and horizontal. These elements are coupled reciprocally. Namely, if one exchanges the role of emitter and receiver, the observed propagation is the same. Nonetheless, there is no knowledge of the impact of non-reciprocal coupling on the propagation of nonlinear waves. Based on an experiment using a liquid crystal light valve (LCLV) with optical feedback, non-reciprocal nonlinear wave propagation can be studied in a one-dimensional chain discrete model. A spatial light modulator and an optical feedback loop let us control the initial conditions and non-reciprocal coupling, respectively. The nonlinear waves' spatiotemporal evolution and velocities are also characterized. A discrete model of the bistable system is derived using a tight binding-like approach for the LCLV with non-reciprocal optical feedback. Numerical simulations of the non-reciprocal coupled bistable system reasonably agree with experimental observations.

Augmented and virtual reality displays require the use of thin liquid crystal cells, with thickness of the order of 1-2 µm. Here, we demonstrate a method, based on cross-polarised intensity measurements coupled to a Frank-Oseen model of the liquid crystal alignment, to characterise such thin cells and the interactions between the liquid crystal and the cell substrates. We first use wedge shaped cells to calibrate the measurement process and show that the cross-polarised intensity data can be used to reliably characterise cells with a non-uniform thickness profile. Previously, we have shown that we can characterise optically thin cells (cells with a phase lag of less than 2π). In this report we apply the method to characterise the optical properties of cells with a non-uniform thickness profile and geometrically thin cells. We show that reducing the thickness of the cell increases the pretilt.