This PDF file contains the front matter associated with SPIE Proceedings Volume 12207, including the Title Page, Copyright information, Table of Contents and Conference Committee list.

The photorefractive effect of flexoelectric smectic liquid crystal mixtures was investigated and applied to a laser ultrasonic measurement. Smectic liquid crystal mixtures, composed of smectic-C liquid crystals, photoconductive chiral compounds, and a sensitizer, are known to exhibit a fast photorefractive effect. The principle of the ultrasonic measurement is that a nanosecond laser pulse is shot on an object to cause an ultrasonic vibration, a continuous laser beam is irradiated on the object, and the ultrasonic variation is detected using photorefractive two-beam coupling. This method can be used to investigate the thickness and the internal structure of an object without contact.

Optical coupling in pattern-forming systems brings out the emergence and transition of complex spatiotemporal behaviors. A liquid crystal light valve experiment with translational optical feedback shows the appearance of striped patterns. When the translational coupling length increases, the system exhibits transitions to traveling, spatiotemporal intermittency, and defect turbulence of striped waves. From the first principles, an order parameter equation valid close to the nascent of bistability together with a translationally coupling is derived. The dynamics of the liquid crystal light valve with translational optical feedback and the proposed minimal model system show qualitative agreement.

Cholesteric liquid crystals (CLCs) show a polarization-sensitive photonic band gap (selective reflection band), the band edges exhibiting resonant optical modes for circularly polarized light. In a theoretical treatment, we discuss the optics of cholesteric ring resonators, where the light is confined to a closed path along the cholesteric helix, which is bent into a circle. Apart from the well-known cavity and band-edge resonances, introduction of an artificial defect (defect layer and/or discontinuity of the director orientation) gives rise to additional resonant modes inside the photonic band gap (defect modes). Such systems show a unique combination of ring cavity, band edge, and defect mode resonances.

Influence of in-plane only retardation switching of an SSD (Smectic Single Domain) liquid crystal both on light diffraction efficiency and beam steering performance has been investigated. An SSD liquid crystal’s in-plane only retardation switching keeping its molecular director always perpendicular to the externally applied electric field is reasonably assumed to provide unique performance both on light diffraction and beam steering. The in-plane only retardation switching was confirmed with polarimetry and light throughput dynamic profiles both for linearly and circularly polarized incident beams. Using the SSD liquid crystal, < 1 ms response with up to 6 degrees steering has been confirmed.

Graphene oxide liquid crystal has very interesting optical and electro-optic properties. In fact, reorientation occurs already at few volts per millimeter and the disk-like graphene oxide flakes, typically suspended in water, can form liquid crystal phases at very low concentration due to the large aspect ratio of the flakes. The liquid crystal formation depends on the flake size, their concentration but also on the magnitude of the repulsive and attractive inter-flakes forces. However, the spatial confinement has relevance too on the macroscopic alignment and even in inducing birefringence as visible in filaments and in more confining configurations. Unlike graphene, graphene oxide has a very small light absorption in the visible, in some regions actually negligible. However, even if the colloidal characteristics are preserved and there is still birefringence, the optical characteristic can change due to near-UV exposure, resulting in an increase of optical absorption. This has the consequence that the imaginary part has to be included in the general refractive index expression and in the optical transmission evaluation. Stability is an important aspect for graphene oxide suspensions either for changes in the optical characteristics or the destabilization of the suspension due to partial or total reduction leading to the formation of reduced graphene oxide, but also for the isotropic – nematic phase separation occurring for concentrations in the bi-phase region. All these aspects are very relevant also for electro-optic applications. It will be shown here that some issues can be solved and improved if the chosen phase is the nematic phase.

Two methods for designing a continuous optical beam steering device are to use a linear phase profile based on physical optical pathlength (OPL) , and based on Pancharatnam phase (PP) . There are challenges with both of these basic approaches when considering design goals of high steering angle range, resolution, speed, and efficiency. In this overview talk, a comparison will be made between these two approaches with regard to these design goals. The limiting effects on each of these design goals will be considered with detailed FDTD optical modeling, and compared with experimental measurements.

Thanks to their giant Kerr-like nonlinear optical response, liquid crystals support the existence of spatial optical solitons called nematicons. These solitons can be experimentally imaged in a microscope thanks to the fluctuation-induced scattering of the laser beam, but the associated microscope images are generally hard to interpret due to the incoherent nature of light scattering. In this contribution, we introduce a theoretical framework allowing to simulate microscope images originating from bulk scattering sources. We apply this framework to the visualization of bouncing solitons, and show that our framework could be the basis for a novel tomography technique of optical fields.

We demonstrate experimentally that diffraction of light incident obliquely at the oblique helicoidal cholesteric (ChOH) structure results in scattering at both the half- (P/2) and the full pitch (P) periodicities. Transmission spectra at P and P/2 are observed in the Vis spectral range, tunable by the electric field and the angle of light incidence. Diffraction at P/2 shows two distinct spectral bands for p- and s-polarized incident light. Diffraction at P is a single wide band. Unique optical properties of ChOH are attractive for applications such as electrically tunable band-pass filters, optical rotators, and beam-steering devices.

A novel beam steering angle expander is demonstrated by cascading two polymeric liquid crystal polarization lenses with different diopters. The lens module functions as a planar telescope, which offers some attractive features such as high precision, lightweight, and low cost. The magnifier offers wide-angle, continuous steering when integrated with an active fine-angle beam steering device. The potential application for LiDAR is emphasized.

Several morphologies are observed in out-of-equilibrium systems. They can be highly symmetric as stripes, hexagons, or squares, and more complicated such as labyrinthine patterns. These shapes arise in different contexts, ranging from chemistry, biology, and physics. Here we study the emergence of chiral labyrinthine patterns near the winding/unwinding transition of a chiral liquid crystal under geometrical frustration. The patterns emerge due to morphological instabilities of cholesteric fingers of type 1. Experimentally, we show that when heating the cholesteric liquid crystal cell at different rates, the winding/unwinding transition is remarkably different. At low rates, chiral fingers appear and exhibit a serpentine instability along their longitudinal direction. At higher rates, after the chiral fingers nucleate, the splitting of their rounded tips and side-branching along their body is observed. Both mechanisms create labyrinthine patterns. Theoretically, based on an amplitude equation inferred by symmetry arguments, we study the morphological instabilities and characterize them by their interface curvature distribution. We discuss the possible velocity-curvature relationship of the finger rounded tips..

Functional soft materials with controlled molecular alignment are attracting much attention in various fields due to their excellent flexibility and functional properties. Among conventional alignment methods, mechanical methods such as rubbing the polymer surface are well-known as a facile route to align various molecules. Besides, photoalignment methods, using photoresponsive molecules and polarized light, enable precise alignment control towards advanced functions. As a novel alignment method combining the advantages of both mechanical and photoalignment methods, we have developed scanning wave photopolymerization (SWaP) where phototriggered molecular diffusion is applied to align molecules. Since it uses the molecular diffusion as a driving force for alignment control, SWaP has the potential to align a variety of molecules. For further exploration of the mechanism, it is necessary to understand the polymer properties; thus, the synthesis of polymers applicable to solution-based analyses is highly desired. In this study, we conducted SWaP to synthesize soluble liquid-crystalline polymer films with one-dimensional alignment. Furthermore, we compared the molecular alignment behavior between SWaP and the conventional rubbing alignment technique using a soluble polymer, and revealed that only SWaP can induce a unidirectional molecular alignment in film.