This PDF file contains the front matter associated with SPIE Proceedings Volume 10361, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Liquid crystal materials with tendency to bend are capable of forming a unique type of a helicoidal structure in which the director is titled with respect to the helicoidal axis rather than orthogonal to it, as in regular cholecterics. The new state occurs in presence of an electric or magnetic field. It is called a cholesteric with oblique helicoidal structure or simply a twist-bend cholesteric, since both twist and bend deformations are characteristic of the ground state supported by the external field. Tilted configuration of the director and absence of density modulation makes the twist-bend cholesterics a unique material for various electro-optical applications. The presentation discusses electrically and magnetically tuned selective reflection of light as well as tunable lasing enabled by these materials. It is demonstrated that the electro-optical performance of the twist-bend cholesterics depends strongly on the type of anchoring conditions imposed by the boundaries of the cell. The work is supported by NSF grant DMR-1410378.

Small molecule chiral nematic LCs contain a variety of defect lines which can cause aggregation of polymers, nanoparticles and small molecule materials such as fluorescent dyes. While normal dyes suffer aggregation induced quenching a class of propeller-like dyes display aggregation induced emission (AIE), which makes them an ideal material for cholesteric lasers. Nanoparticle dispersion is necessary for switchability, while aggregation can be used as a tool to produce assembled structures. Here we discuss strategies to promote or inhibit aggregation of various materials in chiral nematics.

The uniform lying helix (ULH) structure in a cholesteric liquid crystal (CLC) cell has been widely discussed in the literature. Based on the electrohydrodynamic (EHD) effect, we have suggested that the voltage-induction of a wellaligned ULH state can be fine-tuned in a CLC cell by optimizing both the amplitude and the frequency of the applied voltage. However, since the EHD effect is correlated with the migration of mobile ions within the bulk of the cell, the ionic conditions for such an EHD-induced ULH state have not been clarified. In this research, we focus on studying the influence of ion density and the diffusivity on the formation of the EHD-induced ULH structure in a CLC cell, followed by finding out some key conditions for the generation of well-aligned ULH states.

Aggregation-induced emission (AIE) has drawn continuously growing attention due to its great potential in material science and biological techniques. The AIE effect is expected to conquer the notorious aggregation-caused quenching (ACQ) encountered by conventional luminescent materials, and thus realize the high-performance organic light-emitting diodes (OLEDs) without complicated doping method. Our recent studies have demonstrated that it is feasible. The solid-state luminescent materials created by melting AIEgens with conventional chromophores that suffer from ACQ problem at the molecular levels exhibit high photoluminescence efficiency up to unity, and function efficiently as light-emitting layers in non-doped OLEDs. Tunable electroluminescence colors from blue to red and excellent efficiencies approaching theoretical limit are attained by the devices. In addition, rational modifications on AIEgens with carrier-transporting functional groups can endow the luminescent materials with not only high solid-state emission efficiencies but also good hole- or electron-transporting abilities. The non-doped bilayer OLEDs fabricated by utilizing these multifunctional materials as light-emitting and hole-transporting (electron-transporting) simultaneously afford remarkably high efficiencies. These results clearly manifest the practical utility of the AIE effect in development of active materials for OLEDs.

In recent year, optical and polarization vortex (OV and PV) beams, which has phase and polarization singularities, have much-attracted attention in various research fields due to their unique physical properties. In this presentation, we report our attempts for the vortex beam generation based on the photo-alignment technique of functionalized liquid crystal polymers. The OV and PV beam generations are respectively demonstrated by using azo-dye-doped liquid crystal polymers and photocrosslinkable polymer liquid crystal. Our approaches realize highly functionalized vortex beam generators which are expected to evolve the photonics applications of vortex beams.

We investigated the dynamics of photoinduced nematic-isotropic transition especially the back relaxation time and its influence on three different parameters. The parameters are (a) Order parameter: the temperature dependence of the response time was calculated in a material exhibiting a photostimulated isothermal Nematic-Isotropic transition. Using a simple description we show that the temperature dependence of this response time can be understood in terms of the order parameter excess between the equilibrium and photostimulated states. (b) Electric field: application of an electric field accelerates the recovery of trans isomers from the photoinduced cis isomers. An important consequence of this effect is the rapid return of the equilibrium nematic phase from the photo-driven isotropic phase of liquid crystals. (c) Confinement: by confining liquid crystals in an in situ created network of aerosil particles. The DSC scans taken at slower rates for a particular composite in the soft gel regime have a two-peak profile across the N-I transition. In contrast, the bulk has a single peak at all rates investigated. The double peak profile is associated with a crossover from random-dilution to random-field regime. The dielectric measurements, which are the first such measurements on the photoisomerization-driven isothermal phase transitions in LC-aerosil composite bring out several interesting features including the dependence of the photo-driven shift in the transition temperature and the response time on the concentration of aerosil.

We designed the fast switching & low driving voltage principle with nano slippery interfaces in nematic gels. Confinement effect by the gel network can accelerate the response time of nematic due the localization of director motion as similar way to the cholesteric blue phase. However, the anchoring of the director on the gel network induces the driving voltage. Slippery effect on the nano interface of the gel network can reduce the driving voltage due to the lubrication of the director motion. Since azo dye acrylates are co-polymerized with nematic gels (Azo-NGel), we can demonstrate the UV-switchable nano-slippery interface on the nematic gels. Dynamic Light Scattering (DLS) provides us the information of the dynamics of director rotation. Dispersion relation of the pure 7CB-T15 mixture completely satisfies the prediction of hydrodynamic modes in the nematic. On the contrary, the relaxation frequency of the Azo-NGel keeps fast response in the low wave-number region due to the confinement effect. Electro-Optic response (EO) of the Azo-Ngel without UV illumination shows the serious increase of the driving voltage compared to the pure 7CB-T15 mixture. When the Azo-Ngel is illuminated by UV-light Slippery interfaces can be created by the trans-cis isomerization of the Azo dye of the side-chain on the nano network of nematic gels. EO under UV illumination shows the drastic reduction of the driving voltage keeping the fast response time. We have also confirmed that the dispersion relation of the UV illuminated Azo-Ngel is almost the same as that of Azo-Ngel without UV illumination by the DLS measurement. Thus, the confinement effect for the nematic gels is still effective after the slippery interface is created by the UV illumination. We success to demonstrates that the acceleration of the response time is compatible with reduction of the driving voltage by the localization and lubrication of director motions due to the design of the nano-slippery interfaces in the nematic gels.

Photo-alignment technology is important for liquid crystal (LC) device applications where both high resistance to incident optical energy and spatially distributed alignment states over the device clear aperture are required. Coumarin-based photo-alignment materials developed at the Laboratory for Laser Energetics (LLE) possess near-IR laser damage resistance approaching that of fused silica and have been employed in the development and fabrication of a wide variety of LC high-peak-power laser optics. One example is a photo-patterned LC beam shaper, developed for use in LLE’s four-beam, petawatt-peak-power OMEGA EP laser, that has demonstrated 1054-nm, 1 ns laser-damage thresholds approaching those of dielectric thin-film Brewster’s angle polarizers (30 to 40 J/cm2). Achieving similar performance levels in LC devices for near-UV applications is challenging due to a scarcity of both UV-transparent LC materials and polymer alignment layers that can withstand repeated exposure to intense pulsed- or CW UV irradiation without degradation. Previously-employed alignment materials for UV-LC devices such as buffed polyvinyl alcohol (PVA) or Nylon 6/6 have limited usefulness; buffing embeds particulates and scratches into the alignment layer that reduce its UV damage thresholds to only a few J/cm2 and is incapable of producing highly resolved and spatially-distributed LC alignment states. In recent experiments, we have found that coumarin photoalignment materials are remarkably more resistant to damage from both incident 351 nm, 1 ns high-energy laser pulses [~11.42 J/cm2 (1-on-1) and ~15.70 J/cm2.(N-on-1)] and broad-band, continuous wave (CW) UV-visible light than would be expected due to their highly conjugated aromatic electronic structures. This finding opens a new chapter in the development of LC devices for UV applications in high-peak-power lasers (e.g. wave plates, polarization rotators, radial polarization converters, photo-patterned beam shapers) and other areas of optics and photonics where UV stability is important (e.g., space-based applications).

Mesoscopic hierarchical superstructures bridge the micro and macro worlds and play vital roles in natural materials. To mimic hierarchical organization in nature, one promising strategy is the convergence of top-down microfabrication and bottom-up self-assembly. Much efforts have been devoted to this field, but till now, the precise realization and rational control of large-area perfect hierarchical superstructures is still challenging. On the other hand, Smectic liquid crystals (SLCs) are formed by flexible molecular layers of constant thickness. If the nanometer-thin smectic layers can be manipulated in an origami manner, a Japanese art that constructs various 3D objects via folding pieces of papers, brand new hierarchical superstructures possessing exceptional features then could be realized. In this work, the smectic layer origami is accomplished via preprogrammed photoalignment. The principle is rooted in the anisotropy of molecular interactions at interfaces, which makes the preset patterned alignment favoring a certain layer bending of adjacent SLCs, and subsequently dominating the configuration of entire family of smectic layers. Thanks to the excellent flexibility of photoaligning, the unit geometry (shape, size and orientation) as well as the clustering characteristic (lattice symmetry) of fragmented TFCDs can be rationally designed and freely manipulated over square centimeters. The obtained fragmented toric superstructures break the rotational symmetry while maintain the radially gradient director field, enabling metasurface-like direction-determined-diffraction. We believe this work is an important step toward extending the fundamental understanding of self-assembled soft materials and enhancing the construction of possible hierarchical superstructures. It may inspire extra possibilities in advanced functional materials and fantastic photonic applications.

The template effect of self-assembly twist structure liquid crystal (LC) is investigated. The anchoring energy of blue phase (BP) template containing different concentration of conventional polymer has been investigated that every different polymer system had its own threshold concentration to reconstruct the blue phase. The anchoring energy of the BP template increased with the polymer concentration resulting in the improvement of the reconstruction capacity. No matter with the same-handed or reverse-handed chiral materials refilling, there was a concentration range for the chiral dopant to reconstruct the blue phase by the polymer template. And the reconstruction range of the templates was extended as the polymer concentration of the template increased. It was demonstrated that the template anchoring energy has a threshold value to reassemble the double twist cylinder structure of BPLC by either refilling same-handed chiral materials or reverse-handed chiral materials which may help to improve the driving capacity of the polymer stabilized BPLC. Similar to the BPLC, a sphere phase template was proposed to improve the temperature range of sphere phase (SP) to more than 175℃.By template processing, a wavelength tunable random lasing was demonstrated with dye doped SPLC. With different polymer concentrations, the reconstructed sphere phase random lasing may achieve more than 40nm wavelength shifting by electrical field modulation. And the threshold energy of SPLC random laser can be lowered to about 30% of that from the chiral nematic phase LC.

Cholesteric liquid crystals (CLC) has the advantage of large nonlinearity and fast response. This brings great convenience to its applications in ultrafast nonlinear photonic. Here, several kinds of nonlinear phenomenon and applications are reported, such as optical soliton, modulation instability, optical diode effect and pulse compression of cascade CLC samples.

The anisotropic properties of nematic liquid crystals result in polarization dependency which leads to requirement of at least a polarizer in liquid crystal photonic devices. To develop polarizer free phase modulation, Kerr effect is one of the path. The phase modulation in polymer dispersed liquid crystals (PDLCs) is shown to have two parts: Kerr phase, which is the optical phase modulation linearly proportional to a square of electric field, and orientational phase. However, many puzzles are still under investigation: the origins of Kerr phase, the relation between Kerr phase and orientational phase, and how two-steps of electro-optical (EO) response relates to Kerr phase and orientational phase. We investigated the origins of Kerr phase and orientational phase in PDLC and their connection to two-step EO response. In our study, the Kerr phase is a result of LC orientation in the center of LC droplets. The orientational phase attribute to orientation of LC molecules near LC-polymer interfaces. The two phase in PDLC samples are adjustable depending on droplet size. We also found that two-steps EO response existing in small droplet (<33 nm) is related to Kerr phase and orientational phase. A modified PDLC model related to the Kerr phase and orientational phase is also proposed. Besides the conventional features of PDLC, such as polarization independent optical phase shift and response time independent of cell gap, we believe the Kerr phase and orientational phase with different response times (~ msec) in PDLC pave a way for designing versatile photonic devices with pure optical phase modulation.

Studies of chiroptical effects of chiral ligand-capped gold nanoparticles (Au NPs) are a fascinating and rapidly evolving field in nanomaterial research with promising applications of such chiral metal NPs in catalysis and metamaterials as well as chiral sensing and separation. The aim of our studies was to seek out a system that not only allows the detection and understanding of Au NP chirality but also permits visualization and ranking — considering size, shape and nature as well as density of the ligand shell — of the extent of chirality transfer to a surrounding medium. Nematic liquid crystal (N-LC) phases are an ideal platform to examine these effects, exhibiting characteristic defect textures upon doping with a chiral additive. To test this, we synthesized series of Au NPs capped with two structurally different chiral ligands and studied well-dispersed mixtures in two nematic liquid crystal hosts. Induced circular dichroism (ICD) spectropolarimetry and polarized light optical microscopy (POM) confirmed that all Au NPs induce chiral nematic (N*-LC) phases, and measurements of the helical pitch as well as calculation of the helical twisting power (HTP) in various cell geometries allowed for an insightful ranking of the efficiency of chirality transfer of all Au NPs as well as their free ligands.

Liquid crystal (LC) provides a suitable platform to exploit structural motions of molecules in a condensed phase. Amplification of the structural changes enables a variety of technologies not only in LC displays but also in other applications. Until very recently, however, a practical use of LCs for removable adhesives has not been explored, although a spontaneous disorganization of LC materials can be easily triggered by light-induced isomerization of photoactive components. The difficulty of such application derives from the requirements for simultaneous implementation of the following essential requisites: (i) adequate strength for a temporary bond (more than 1 MPa) even under heating conditions, (ii) significant reduction of the bonding strengths by light irradiation, and (iii) quick photoresponse for the separation of bonded materials. Here we present a liquid crystal (LC) material that satisfies all of the above-mentioned requisites for the light-melt adhesives, namely, (i) a shear strength over 1 MPa up to 110 °C for bonding glass plates, (ii) an 85% reduction of the strength by ultraviolet (UV) irradiation, and (iii) an instant photomelting of the LC film in a few seconds. Moreover, this material is reusable as an adhesive, and the transformation between the LC and melted phases is associated with an informative color change in fluorescence. We envision that composite materials with the light-melt function will further improve the performance in manufacturing processes, which will accelerate the on-demand photoseparation technology complementary to the other switchable adhesion approaches.

Recent developments in photoalignment of liquid crystals (LCs) brought to the market photoreversible materials such as azobenzene-based PAAD complex dyes [1], which quickly found broad photonics applications for constructing diffraction elements and waveplates [2,3]. Despite extensive investigations of photoaligned LC systems, there is little information on the optical properties such thin PAAD layers. Here we report an experimental investigation of optical properties, such as refractive indices and absorption coefficients for different PAAD materials, namely PAAD-22D, 22E and 22N. Photoinduced phase gratings were recorded in 20-50 nm thick PAAD layers with no evidence of a corresponding surface relief, which is a typical feature in thicker azobenzene films. Therefore, the formation of the gratings is attributed to optically induced birefringence. The investigated materials exhibited different values of birefringence, reaching 0.025, and significantly different temporal response to laser irradiation. Moreover, the diffracted power was observed to be very sensitive to the polarisation of the probe beam with respect to that of the pump beam. We also studied photoinduced diffraction in PAAD-LC systems, where we observed the formation of a stable and strong diffraction pattern. The gratings can be rewritten by illumination with another light pattern or switched off by reorienting liquid crystals with a bias voltage. A diffraction efficiency of more than 5% was measured in a cell containing PAAD-22D in combination with 8μm thick LC-E7 layer. Finally, we compare the dynamics of light induced response in the PAAD layers and PAAD-LC cells and investigate their respective memory effects. [1] Beam Engineering for Advanced Measurements Company, Winter Park, FL 32789. [2] Vernon, J. P., et al., Opt. Express 21, 1645 (2013). [3] Nersisyan, S. R., et al. Opt. Express 21, 8205 (2013).

Computational chemistry tools such as density functional theory (DFT) have seen increasing application in the design and development of new organic optical materials, organic light emitting diodes (OLED) and liquid crystals. In previous work, we employed DFT to model the trans–cis isomerization state energies in a series of methacrylate and acrylamide photoswitchable polymer alignment materials functionalized with azobenzene pendants connected through a flexible alkyl chain (tether). Such photoswitchable alignment materials are of interest for LC devices for beam shaping due to their remarkable 1054 nm, 1 ns laser damage thresholds (28 to 67 J/cm2) and their ability to support spatially-varying write-erase capability. These modeling efforts were confined to a small representative section of the photoaligment polymer (an oligomer) composed of one tethered chromophore and four repeat backbone segments to reduce the large amounts of computational resources and time that would be required to accurately model a complete polymer system. Twenty-two different terminal functional groups were evaluated computationally to determine their individual effects on the trans and cis isomerization-state energies of the methacrylate and acryamide oligomers when used as substituents on azobenzene cores linked through a four-carbon tether to methacrylate and acrylamide backbones. The contribution of the alkyl tether to the isomerization-state energies of the methacrylate and acrylamide oligomers was also investigated computationally. This work extends the previous study by using DFT to evaluate the effect of molecular structure and tether length on the transition state energy barrier separating the pendant’s isomeric switching states, which can have a large effect on bistability, write-erase fatigue, and switching energy requirements. Both oligomers containing azobenzene and spiropyran photoswitchable pendants were modeled in this study.

We report here on cell growth and proliferation within a 3D architecture created using smectic liquid crystal elastomers (LCEs) leading to a responsive scaffold for tissue engineering. The investigated LCE scaffolds exhibit biocompatibility, controlled degradability, with mechanical properties and morphologies that can match development of the extracellular matrix. Moreover, the synthetic pathway and scaffold design offer a versatility of processing, allowing modifications of the surface such as adjusting the hydrophilic/hydrophobic balance and the mobility of the LC moieties to enhance the biomaterial performance. First, we succeeded in generating LCEs whose mechanical properties mimic muscle tissue. In films, our LCEs showed cell adhesion, proliferation, and alignment. We also achieved creating 3D LCE structures using either metallic template or microsphere scaffolds. Finally, we recorded a four times higher cell proliferation capability in comparison to conventional porous films and, most importantly, anisotropic cell growth that highlights the tremendous effect of liquid crystal moieties within LCEs on the cell environment.

A method and system for imaging objects based on sensing their dielectric permittivity at low frequencies of few kHz are presented. The system is composed of three regions: Liquid Crystal (LC) layer, buffer layer and a cavity in which the analyzed samples are inserted. When a voltage is applied, it falls partially on the LC causing its molecules to tilt. The amount and distribution of the voltage depend on the dielectric permittivity of the analyzed samples. The permittivity distribution is imaged by reading the retardation changes in the LC with visible light in reflection and transmission modes. The resolution limit of the system is predicted theoretically using rigorous simulation showing possible resolution down to few tens of microns.

The optical power of diffractive waveplate structures is limited not as much by fabrication technology issues as by the fundamental features of light propagation in complex anisotropic structures. The infinitely thin two-dimensional film approximation does not apply, and the efficiency of 4G lenses, prisms, etc., is reduced for geometries corresponding to sharp focusing lenses and large diffraction angles. Due to thin-film nature, these films can be combined to reduce effective focal length, increase effective diffraction angle, topological charge, etc. Along with this, we will discuss the opportunity of increasing optical power of 4G lenses, prisms, etc. without compromising efficiency.

By illuminating a photo-alignment layer with two interfering UV laser beams with opposite circular polarization, a periodic alignment pattern is obtained for nematic liquid crystal. In a liquid crystal cell two substrates are used with periodic photo-alignment, with the periodicities perpendicular to each other. After filling with nematic liquid crystal the director obtains a 3D pattern with period twice that of the photo-alignment. The resulting 3D structure depends on the cell thickness (between 3 and 20 m) and the periodicity of the photo-alignment (also between 3 and 20 m). The director pattern can be estimated by performing numerical simulation with a Q-tensor method. The simulation results can be verified by polarization optical microscopy or by observing the diffraction properties of the structure. For a long range periodicity combined with a small period, the light is efficiently distributed over a small number of diffraction orders. The director pattern can be reoriented by applying a potential difference between the two substrate electrodes. Optical and electrical steering is investigated for devices with different dimensions.

Loss of distance accommodation is a common disease and many approaches have been considered to solve this problem. Some of them are based on the use of mechanical force. However, we have developed an alternative approach using motion-free focusing based on liquid crystal lenses. Electrical distance triggering mechanism was also developed. The optical, energy and size characteristics will e presented.

Exciting experimental results on the response properties of hybridized photo responsive liquid crystal test cells are reported, where iron doped lithium niobate substrates were used to photo generate electric fields and indium tin oxide coated cover glasses were used to confine these photo generated fields in a liquid crystal layer. Samples were investigated in a modified inverted optical polarizing microscope with white probe light (crossed polarizers) and exposed with a Gaussian laser beam focused to a small spot (14 μm FWHM). Test cells filled with nematic LC showed homeotropic director alignment. Upon exposure, this alignment was maintained at the exposure spot center and the LC director was selectively realigned in a surrounding single ring. This ring had a thickness of a few microns and its diameter increased with increasing exposure intensity (112 μm at 0.7 mW, 204 μm at 1.1 mW). This characteristic director realignment was traced back to the optically generated electric field distributions by simulations. In samples filled with chiral nematic LC, uniformly standing helix alignment was found. Textural transitions were induced at the focus position, which again led to the formation of well-defined circular defects. We could show that these defects can be permanently stored within the chiral nematic LC. Polarized optical microscopy of a rotated sample revealed that a point like defect with +1 topological charge was enclosed in each of these defects. Photovoltaic fields generated in small lithium niobate particles dispersed in a LC were found to cause promising optical responses and particle movement.

All diffractive lenses manifest chromatic aberration/dispersion. If the focal length f0 at a given wavelength λ0 is known, then the focal length f(λ) = f0 λ0 / λ at other wavelengths λ. This can be considerable, even for lenses of a few diopters. Geometric-phase lenses (GPLs), are no exception, which manipulate incident light’s wavefront by the Pancharatnam-Berry phase effect. Several years ago, we developed achromatic coatings based on photo-aligned chiral liquid crystals that achieve nearly 100% efficiency into the primary and conjugate waves, and more recently we demonstrated fast, defect-free GPLs down to F/1.5 for red light. Until now, no one has reported how to generally reduce chromatic aberration and ensure that two or more wavelengths can have the same focal length. Here, we report on a new approach to correct for chromatic aberration using a stack of GPLs and retarders to arrange red, green, and blue wavelengths to have precisely the same focal length. A simple arrangement of these elements results in a thin, monolithic, and flat GPL, which can either converge or diverge three wavelength sources (R/G/B) with the same focal length, positive or negative, depending on the handedness of the circular input polarization. Here, we describe the concept and characterize our first prototypes by evaluating focal lengths, efficiency, and polarization contrast. We also discuss the realistic opportunities and limitations for this approach.

The control of the molecular orientation of liquid crystals (LCs) is important in both understanding phase properties and the continuing development of new LC technologies including displays, organic transistors, and electro-optic devices. Many techniques have been developed for successfully inducing alignment of calamitic LCs, though these techniques typically do not translate to the alignment of bent-core liquid crystals (BCLCs). Some techniques have been utilized to align various phases of BCLCs, but these techniques are often unsuccessful for general alignment of multiple materials and/or multiple phases. Here, we demonstrate that glass cells treated with polydimethylsiloxane (PDMS) thin films induce high quality homeotropic alignment of multiple mesophases of four BCLCs. On cooling to the lowest temperature phase the homeotropic alignment is lost, and spherulitic growth is seen in crystal and crystal-like phases including the dark conglomerate (DC) and helical nanofilament (HNF) phases. Evidence of homeotropic alignment is observed using polarized optical microscopy. We speculate that the methyl groups on the surface of the PDMS films strongly interact with the aliphatic tails of each mesogens, resulting in homeotropic alignment.