Electrochromic devices have found widespread use in automotive, aerospace, and architectural implementations. This talk will detail our recent research of liquid crystalline compositions in which the selective reflection can be tuned, broadened, and switched by mechanical, thermal, or electrical stimuli. Enabled by the modularity of the formulation of the cholesteric liquid crystal phase, filters can be prepared throughout the electromagnetic spectrum (VIS, NIR, SWIR, MWIR).

An optically addressable liquid crystal spatial light modulator (SLM) is used for dynamic laser beam shaping used in a unique, fast metal additive manufacturing process [1]. We address challenges of using our SLM exposed continuously to high power kW-MW lasers. Control of liquid crystals is coupled to the potoexcitation-response of photoconducting insulators that affects contrast, switching speed, and laser power handling. We compare liquid crystal materials laser damage rationalized based on their thermal properties, and highlight device-level stresses via computational modeling. Key areas of liquid crystals and semiconductor properties are presented that impact optically addressed SLM for power switching applications. [1] https://www.seurat.com/area-printing

Precise control of the surface topographies of polymer coatings is crucial to developing high-performance materials and devices for a wide variety of applications, such as optical displays, micro/nanofabrication, photonic devices, and microscale actuators. Mainly, photocontrolled polymer surfaces, such as photoinduced surface relief, have been studied through photochemical mass transport. In this study, we propose a novel method triggering the mass transport by photopolymerization of liquid crystals with structured light and demonstrate the single-step formation of microscale well and canal structures on the surface of polymer films. Such well and canal structures can be arranged in two dimensions by designing light patterns.

One of the most ancient forms of life dating to ~3.5 billion years ago, cyanobacteria are highly abundant organisms that convert light into energy and motion, often within conjoined filaments and larger colonies. We study how gradients of light intensity trigger orderly phototactic motions and dense bacterial communities, which remained quantitatively unexplored despite being among the oldest forms of active living matter on Earth. The phototaxis drives a transition from initially polar motions of semiflexible long filaments along complex curved spatiotemporal trajectories confined within illuminated areas to their bipolar motility in the ensuing crowded environment. We demonstrate how simply shining light causes a spontaneous self-assembly of two- and three-dimensional active nematic states of cyanobacterial filaments, with a plethora of motile and static topological defects. We quantify light-controlled evolutions of orientational and velocity order parameters during the transition between disordered and orientationally ordered states of our photosynthetic active matter, as well as the subsequent active nematic's fluid-gel transformation. Patterned illumination and foreign inclus

Light-powered micro-machines, also known as shape-memory robots, have been studied for their versatile ability to crawl, roll, jump, and slide, whereas liquid crystal polymer networks (LCNs) are extensively used. While these stimuli-responsive materials for soft microrobots claim to have achieved microscale size, they have only managed to realize the micro-thickness, rather than the entire size. This paper demonstrates a methodology for constructing light-activated 3D micro-robotics using two-photon polymerization. This approach enables the development of sophisticated architecture in tens of microscales of soft actuators, which could pave the way for the creation of cell-sized micro-robotic systems.

New findings in the field of research have brought to light a unique heating effect caused by pseudo-dielectric relaxation in negative nematic liquid crystal cells. This effect, known as pseudo-dielectric heating (PDH), has often been mistakenly associated with dielectric heating (DH), which originates from the orientational relaxation in, say, dual-frequency liquid crystal (DFLC). Our recent research re-examined the heat-induced dielectric properties in DFLC cells, leading to a new understanding of both DH and PDH. Together with published results through explorations of the application of the PDH effect by multiple research groups, our knowledge of the underlying physics and the potential to utilize this unique physical phenomenon have been established for innovative applications.

Conventional optical microscopes visualize static inhomogeneities such as orientation, concentration, and density within a material. On the other hand, our newly developed fluctuation microscope is a new microscope that directly visualizes the distribution of dynamics within a material as "dynamic inhomogeneity" as a two-dimensional image. We mixed liquid crystal molecule E44 and mesogen molecule with acrylate groups A6OCB and UV-polymerized them in a liquid crystal alignment cell to investigate the dynamics in the material near the liquid-glass transition point of the side-chain polymer swelling system, and near the sol-gel transition point by adding a very small amount of cross-linking agent. As a result, we succeeded in directly observing the characteristics of spontaneous dynamic heterogeneity formation. To investigate the correlation between the dynamic inhomogeneity generation and macroscopic viscoelasticity, simultaneous multi-frequency dynamic Young's modulus measurements were also performed. We found that when the temperature is lowered from the high-temperature nematic phase state, the remarkable dynamic heterogeneity appears in intermediate temperature range.

Controlling the amount of light energy that reaches Earth from the Sun is becoming an issue of utmost importance, according to many scientists. The solutions being proposed range from “dumping chemicals in the oceans, spraying saltwater into clouds, and injecting reflective particles into the sky” to putting a giant parasol in space to shade the Earth. This last idea, the least destructive in this list, has been studied for years with no practical solution in sight. Liquid crystal polymer diffractive waveplates, the fourth generation of optics, offers a highly promising solution due to feasibility of spectrally broadband high efficiency diffraction a with ultralight free-standing optical films with lowest mass for the expected solar energy reduction.

We present an optical learning framework based on reconfigurable liquid crystal/polymer composite (LC/PC) scattering media. Our design leverages multiple scatterings between the LC/PC sample and a spatial light modulator (or a digital mirror device) that encodes the input data to realize random nonlinear optical mapping in a tunable manner. The system is applied to several learning tasks to demonstrate its capabilities. The reconfigurability of the LC/PC can optimize the learning performance, and enable photonic ensemble learning, which further improves the overall performance.

Optoelectronic nanocrystals are of enormous interest for material science and applications including solar cells and light-emitting diodes due to precise tunability of their properties via size and shape. Accordingly, various synthetic methods have been proposed, but achieving monodispersed nanocrystals remains a key challenge leading to the present lack of their commercial value and real-world applications. In this presentation, I will present that unique features of liquid crystals can be leveraged to synthesize nanocrystals with an unprecedented level of control over size and shape. The approach is a simple, rapid, and room-temperature process, yet it enables access to highly homogeneous nanocrystals with substantially reduced surface defects resulting in significantly improved optoelectronic features. The results offer a versatile and generalizable strategy to be broadly compatible with a range of nanomaterials and other synthetic methods. This work was supported by NRF funded by the Korea government (RS-2023-00212739, RS-2023-00302586).

Cholesteric liquid crystals (CLCs) possess a naturally occurring helical structure that produces striking reflective coloration. The inherent electrical response of the chiral nematic phase is limited, but through the use of polymer stabilization novel electrically driven optical properties can be accessed. Polymer stabilized cholesteric liquid crystals (PS-CLC’s) are formed by polymerizing reactive liquid crystals that have been doped into the chiral nematic liquid crystal. These PS-CLCs demonstrate a range of unique optical behaviors when subjected to electric fields, such as shifting colors and variations in spectral bandwidth. These phenomena are linked to the electrical manipulation of the polymer matrix and the corresponding reaction of the surrounding non-reactive liquid crystals. In this talk, we discuss our latest findings in this field, focusing on uncovering the underlying mechanisms of the electrically induced responses and applying these insights to enhance the performance of these materials.

Polarization colors in birefringent media result when the optical rotation of light is transduced into a periodic, wavelength-dependent intensity by the use of polarizers. These colors are the most vivid when there are less than three peaks in the visible regime and are commonly used in optical minerology as an identification tool. In this work, we examine the effect of the dispersion of the nematic liquid crystal 5CB in geometries with micron length scales on polarization colors. Using values from the literature, we compute the spectra and compare them with the dispersionless case using the average value across the visible spectrum. We demonstrate how to convert the spectra into colors and show the significant differences between the dispersive and dispersionless polarization colors. We show that the experimental results using 5CB in wedge cells and electrospun microfibers is in good agreement with our dispersive colorimetric calculations.

Soft matters, such as polymers, liquid crystals, and biomolecules, in which nano-scale molecules are self-organized and self-assembled, possess characteristic properties. Since they show structural, mechanical, and electro-optical properties without losing their flexibilities, soft matters have been utilized for functional materials. For developing these functional soft materials, it is essential to understand the structure and dynamics at both a macroscopic and microscopic point of view. Since the results obtained from only the experiments were not enough to elucidate the origin of the physical properties of the soft materials, molecular dynamics (MD) simulations to provide additional insights at the molecular level are becoming increasingly important. A MD simulation study for the helical columnar liquid crystals exhibited by an octahedral metallomesogen has clarified the molecular packing structure and nano-scaled helical structure of the single column and its mechanism. Also, the microscopic dynamics of the molecules consisting of aqueous-liquid crystal sensors has been elucidated by carrying out MD simulation. Recently, it has been shown for organic semiconductors that dynamic disorder can be analyzed by MD simulation and the molecular assembly structures can be predicted by MD simulation-based computational science approach. MD simulation studies would give us new insights into functional soft materials at the molecular-level.

Turbulence is a complex spatiotemporal behavior and a fundamental concept in fluid dynamics, which has been extended to other systems out of equilibrium, such as nonlinear optics, chemistry, active matter, and economics. Fingerprint patterns with sustained spatiotemporal dynamics in a liquid crystal light valve with an optical feedback experiment are studied. We show that the light intensity field presents a dynamical regime simultaneously exhibiting phase and amplitude turbulence. This bi-turbulent behavior of patterns is characterized by power-law spectra with exponents close to -2 and -3 spatially and -2 temporally, for the phase and amplitude respectively. The pattern orientation field also presents power-law spectra with exponents close to -2 and -3/4, spatially and temporally. We characterize the observed chaotic dynamics by estimating the largest Lyapunov exponent. We provide a theoretical model of pattern formation that explains the experimental observations with good qualitative agreement.

This study presents an electrically-controlled hybrid plasmon-induced transparency (PIT) metadevice leveraging on nematic liquid crystals for enabling active manipulation of terahertz slow light. Achieving Fano-resonant response via near-field coupling of chiral and achiral meta-atoms facilitates nonlinear terahertz generation and mitigates radiative losses. These findings highlight the potential of Fano-resonant active metasurfaces for advanced sensing and slow-light devices.

In this talk, we will introduce a novel photo-alignment material that has been specifically developed for use in liquid crystal optical devices. These materials contain molecules that have at least one anchoring group and one α,β-unsaturated carbonyl group. These groups can include derivatives of carboxylic acid, amides, nitriles, or ketones. When these materials are dip-washed onto the substrate surface of the transparent electrode, such as an ITO layer, the anchoring group, in this case, phosphonic acid, forms a single molecular self-assembled layer. Excellent LC alignment was achieved by these alignment layers when exposed to linearly polarized light.

Inorganic nanorods are promising for the development of advanced devices due to their unique properties. The alignment control of these nanomaterials is crucial to exploit their potential. Various alignment methods, such as electric fields and self-assembly, have been attempted, but it is still a challenge to develop sophisticated methods for aligning nanorods over a large area. In this paper, we present a method for inducing unidirectional alignment of nanorods by utilizing nematic liquid-cyrstalline polymers, which are attractive in their ability to support organized nanostructures due to their anisotropic molecular orientation.

Recently, ferroelectric phenomena have been identified in nematic liquid crystal phases, which have attracted considerable attention. Ferroelectricity is only observed in systems with a special symmetry that lacks an inversion center, and in liquid crystals it has been observed only in chiral smectic C phases, for example. Since nematic phases have been considered to have mirror symmetry and no macroscopic polarization, ferroelectric nematic phases are very interesting from both fundamental and applied viewpoints. We have investigated the orientation behavior of ferroelectric nematic liquid crystals (FNLCs) on various alignment films such as rubbing and photoalignment. Here we report the polarization alignment behavior of ferroelectric nematic liquid crystals on rubbed polyimide and photoalignment films. We will also discuss polarization alignments in cells combining various different oriented films.

On the molecular origins of fluid conglomerates: Two unique classes of fluid conglomerate formed by spontaneous achiral symmetry breaking in one homologous liquid crystal series.

The present study investigates the nonlinear optical response of a cyanobiphenyl liquid crystal (8CB) doped with carbon dots derived from dansyl chloride (CD-DsCl). Using the time-resolved z-scan technique, it is investigated how the CD-DsCl addition affects the nonlinear refractive coefficient of planar liquid crystal samples. The temperature dependence of nonlinear optical responses of pristine and doped samples are analyzed close to smectic-A - nematic and nematic - isotropic phase transitions. Furthermore, the effects of an external electric field are analyzed. Our results show that doped 8CB samples may exhibit an enhanced nonlinear optical response, which depends on the strength of the external field.

Onsager's model of hard spherocylinders demonstrated the isotropic-nematic phase transition, revealing that molecular elongation alone induces liquid crystalline order. Subsequent research expanded this understanding to various anisotropic shapes, including banana-shaped molecules. Recent studies have reported a chiral twist-bend nematic phase in achiral systems [Greco et al. (2015), Phys. Rev. Let., 115(14), 147801]. DFT calculations [Greco et al. (2014), Soft Matter, 10(46), 9318-9323] showed how crescent and cone-like shapes affect elastic constants, confirming earlier observations made by Meyer. Our research group investigated the stability of modulated liquid crystalline phases in crescent and cone-like systems via Monte Carlo simulations. We found stable twist-bend nematic, splay-bend smectic and columnar phases for crescent-like shapes. When subjected to confinement between walls or when two domains with opposite chiralities were juxtaposed, various phases emerged, including splay-bend nematic. While simulations did not confirm DFT predictions for cone-like molecules, we observed crystalline phases with non-trivial domain configurations.

Liquid crystals (LC’s) are remarkably resistant to damage from high-energy single-or multi-pulse laser beams. Their laser-induced damage threshold (LIDT) depends on both the incident laser properties and pi-electron delocalization in the LC molecular structure. Real-time, time-dependent density functional theory (RT-TDDFT) was employed to model changes in pi-electron density distribution in LC’s as a function of time and laser fluence as 1053 nm, 22 fs laser pulses propagated though the material. Electron density maps reveal that changes in-pielectron density distribution become irreversible above a certain threshold fluence, which may signal the onset of chemical changes leading to laser damage.

Soft actuators are recognized as the intelligent robotics of the future. The main difference with other systems is the degree of freedom present and the shape of the stimuli. In this work, we focus on light stimuli and how light interacts with nanomaterials such as carbon nanotubes and hematite nanoparticles. We prepared a monomer based on azo compounds derived from methyl red. Methyl red is known as a photoisomerization agent. LLiquid crystal polymers with azo compounds exhibit photoisomerization with a lower degree of freedom of molecular reorientation than non-polymeric systems. However, photoisomerization not only exerts a transition order-disorder but also generates a stress relaxation process between the polymer chains. Depending on the percentage of components is possible to build different configurations with more or less crosslinked degrees. To incorporate monomers that only have one polymerizable side is possible to obtain an elastomer system and if only using monomers with two polymerizable sides the crosslinking is higher. The incorporation of nanomaterials allows for modifying mechanical properties and can also incorporate some degree of polarization.

Cardiovascular diseases are the leading cause of deaths in the modern world. It is due to a process where the human immunological system acts against modified (mo) Low-Density Lipoproteins (LDL) present in the blood stream. These modifications are, mainly, due to oxidation of the LDL by free radicals present in the blood. Identify the amount of moLDL particles in the blood is of fundamental importance to physicians to determine the patient therapy. The Non-Linear Optics in the thermal regime was shown to identify, by the amplitude of the thermal lens formed during the interaction of the laser light with LDL solutions, the degree of modification of the particles. The technique employed to perform this analysis is the Z-Scan, in the thermal regime. In the talk, details of the technique employed to analyze the blood from different donors, with different pathologies will be presented.

In the current report, we describe the development of an electrically tunable liquid crystal lens (eTLCL), that we name “foveal lens”, and its use in an adaptive excitation and imaging scheme applied to a commercial fluorescence microscope. The proposed approach allows the selection of the zone of interest and exciting mostly this area. This reduces significantly the fluorescence noise produced by the neighboring areas. In addition, we can also image the same zone of interest, further reducing the noise level. The zone of interest may be dynamically (electronically) scanned to cover the entire field of view without any mechanical movement. The basics of its operation as well as of its optical performance data will be reported. We think that this may improve dramatically the operation of fluorescence and other microscopes.

Phased Array Antennas (PAAs) and Reconfigurable Intelligent Surfaces (RISs) have garnered substantial attention for their capacity to astutely manipulate the wireless propagation environment, establishing them as a pivotal technology for enhancing capacity and coverage in 6G communication networks. High-performance phase control unit is the key element for PAA/RIS. This talk presents the design and measurement results of a reflective liquid-crystal (LC) phase shifter in microwave range.

We introduce a novel method for fabricating Polymer Dispersed Liquid Crystal (PDLC) devices using aerosol jet printing (AJP). Our method simplifies PDLC device structure by directly printing the electrode directly onto the PDLC surface during fabrication. This advancement enables non-contact, direct deposition of patterned active optical devices. Miniaturization of such devices have potential in optical logic and neural network systems. We've successfully demonstrated the direct deposition of PDLC films onto non-planar optical surfaces, printing a functional device over the 90° edge of a prism. Surface analysis using Scanning Electron Microscopy reveals the morphology of both the polymer electrodes and the liquid crystal domains within the host polymer. We further demonstrate printed ion gel doped PDLC and report quantification of the electrical and optical properties within spatially restrictive optical systems.