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Electro-optical switching in twisted nematic samples doped with gold nanorods
摘要： The present study is devoted to the investigation of reorientation properties of 8CB liquid crystal samples doped with gold nanorods with distinct aspect ratios. By using an optical experimental setup to probe the electro-optic response of twist cells under an AC electric field, we measure the characteristic switch times and Freedericksz threshold of doped nematic liquid crystals. The effects associated with the surface plasmon resonance and disorder induced by the metallic guest particles are analyzed. Further, we exploit the Gooch-Tarry conditions and Mauguin minima to account the thermal dependence of nematic birefringence in pristine and doped samples. Our results show that the electro-optical and thermal parameters of twisted nematic cells are strongly affected by the addition of gold nanorods.
关键词： Nematic liquid crystals,Gold nanorods,Reorientation
更新于2025-09-19 17:13:59
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Effect of Cell Thickness on the Electro-optic Response of Polymer Stabilized Cholesteric Liquid Crystals with Negative Dielectric Anisotropy
摘要： It has previously been shown that for polymer-stabilized cholesteric liquid crystals (PSCLCs) with negative dielectric anisotropy, the position and bandwidth of the selective re?ection notch can be controlled by a direct-current (DC) electric ?eld. The ?eld-induced deformation of the polymer network that stabilizes the devices is mediated by ionic charges trapped in or near the polymer. A unique and reversible electro-optic response is reported here for relatively thin ?lms (≤5 μm). Increasing the DC ?eld strength redshifts the re?ection notch to longer wavelength until the re?ection disappears at high DC ?elds. The extent of the tuning range is dependent on the cell thickness. The transition from the re?ective to the clear state is due to the electrically controlled, chirped pitch across the small cell gap and not to the ?eld-induced reorientation of the liquid crystal molecules themselves. The transition is reversible. By adjusting the DC ?eld strength, various re?ection wavelengths can be addressed from either a di?erent re?ective (colored) state at 0 V or a transparent state at a high DC ?eld. Relatively fast responses (~50 ms rise times and ~200 ms fall times) are observed for these thin PSCLCs.
关键词： polymer stabilization,cholesteric liquid crystals,red tuning,switching responses
更新于2025-09-19 17:13:59
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A Quantum Dot Polarizer for Liquid Crystal Displays with Much Improved Efficiency and Viewing Angle
摘要： In this paper, a down-conversion polarizer with quantum dots (QDs) integrated is designed for liquid crystal displays (LCDs). By a special optical microstructure design between Polyvinyl Alcohol (PVA) and QDs layers, a raise of luminance by nearly 60% can be achieved both in simulation and experiments. In addition, the viewing angle of such a LCD increases from 55° to 130° and the color gamut expands from 72% to 94% National Television Standards Committee (NTSC) standard which implies a broad prospect for this QD polarizer.
关键词： polarizer,liquid crystals,quantum dots,microstructure
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Self-Written Y-Junctions using Spatial Solitons
摘要： The self-focusing and the formation of spatial solitons attracted a great deal of attention since the early days of nonlinear optics. Essentially a high-power beam changes the refractive index, writing a waveguide capable to con?ne the beam itself. Accordingly, spatial solitons behave like optical waveguides for beams at different wavelength and low power, thus enabling the generation of integrated optical devices written by the light itself. Several all-optical devices have been demonstrated based on this principle, with particular attention devoted in the last two decades to nematic liquid crystals (NLCs) due to their huge nonlinear response. The main nonlinear mechanism in NLC for CW excitations is reorientational, that is, the extraordinary (e-) wave rotates the optical axis of the material, providing a focusing effect. Nonetheless, NLCs are also subject to a strong thermo-optical effect, typically yielding a defocusing effect for the e-wave. Here we demonstrate the excitation of couples of solitons with a single-humped beam caused by the interaction between reorientational and thermal nonlinearity.
关键词： thermal nonlinearity,nematic liquid crystals,reorientational nonlinearity,spatial solitons,nonlinear optics
更新于2025-09-16 10:30:52
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Palladium-induced transformation of nematic liquid crystals to robust metallogel comprising self-assembled nanowires
摘要： The formation of a nematic liquid-crystalline phase in the bulk along with gelation of a novel asymmetric bolaamphiphilic NDI sca?old has been demonstrated. Further, a discrete metal NDI complex that is capable of forming a robust metallogel through wrapping of the NDI core with the oxyethylene chains of the neighboring molecules has been synthesized.
关键词： nematic liquid crystals,Palladium,metallogel,self-assembled nanowires
更新于2025-09-16 10:30:52
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Enhancement of thermal and electro-optical properties of photonic crystal fibers infiltrated with a modified 6CHBT nematic liquid crystal doped with gold nanoparticles
摘要： In this paper we present the obtained experimental results for enhancing the parameters of photonic crystal fibers infiltrated with a modified 6CHBT doped with gold nanoparticles. By admixing a special liquid crystalline material we were able to widen the working temperature range of our samples. Doping our liquid crystal mixture with nanoparticles visibly enhances the thermal and electro-optical properties of the infiltrated photonic crystal fibers. Additionally, the use of a specially designed four microelectrode system allowed to decrease voltage. Thanks to the introduced modifications we noticed a significant reduction of threshold voltages (up to 44%), rise times (up to 30%) and fall times (up to 50%).
关键词： Photonic crystal fibers,Nanoparticles,Liquid crystals
更新于2025-09-16 10:30:52
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On the application of a supercontinuum white light laser for simultaneous measurements of temperature and velocity fields using thermochromic liquid crystals
摘要： Simultaneous velocity and temperature measurements using thermochromic liquid crystals (TLC) as tracer particles are discussed, with regard to measuring range, uncertainty and spatial resolution. For the first time, a supercontinuum laser is used to illuminate these particles, which shall later be used for the characterization of the momentum and heat transfer in Rayleigh-Bénard cells with high aspect ratio using particle image velocimetry (PIV) and particle image thermometry (PIT). Light scattered from the TLCs is analyzed by spectrometer measurements, revealing its general scattering characteristics depending on the angle between the light sheet plane and the viewing axis. It is shown that white light sources with continuous spectral characteristic and a slightly higher fraction of light in the red wavelength range perform well, thereby the supercontinuum white light laser can be used, even though it has a cut-in wavelength of about 475 nm. The numerical aperture of the detection optics and chromatic aberrations of the laser light significantly affect the temperature sensitivity and dynamic range of the color of the TLCs. This may cause an effective temperature sensitivity range of about one-tenth of their nominal range, particularly at large angles between light sheet plane and viewing axis, as usually applied in PIV. A simultaneous velocity and temperature measurement in a Rayleigh-Bénard cell experimentally validates that the use of the supercontinuum laser allows for reliable simultaneous PIV and PIT measurements with high spatial resolution of less than 500 μm in out-of-plane direction, on condition that an appropriate two-dimensional calibration is applied.
关键词： Thermochromic liquid crystals,Supercontinuum laser,Rayleigh-Bénard convection,Particle image thermometry,Particle image velocimetry
更新于2025-09-16 10:30:52
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Sonication-Enhanced Alignment Relay Technique for the Orientation of Single-Walled Carbon Nanotubes
摘要： The high demand for thin, lightweight yet fast and e?cient devices is a driving force behind the miniaturization trend in the electronics industry. Speci?cally, the advancement of semiconducting single-walled carbon nanotubes (SWNTs) can continue to revolutionize transistors, although there are still many challenges ahead. We have previously reported an alignment relay technique (ART) that is capable of simultaneously controlling the alignment, length, and diameter of surface deposited SWNTs. However, the current technique yields inconsistencies in orientation, lengths of tubes, and their density. Here, we present a reviewed ART protocol that includes sonication for improved selectivity. We show that the SWNTs average alignment increased from 40% to 77% within a 10° range in orientation with sonication times as low as 5 min. Sonication generated larger diameter nanotubes on the surface, with a preference for semiconducting chiral tubes in the range of 1.44?1.61 nm in diameter. Consequently, simple alterations to the standard alignment relay technique can prove to be prosperous in improving selectivity and orientational control of single-walled carbon nanotubes. This work has direct impact for the simultaneous control of nanotube alignment and nanotube chiralities.
关键词： alignment relay technique,iptycenes,alignment,sonication,single-walled carbon nanotubes,surface chemistry,liquid crystals
更新于2025-09-16 10:30:52
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Tuneable ferroelectric liquid crystal microlaser
摘要： We demonstrate electric ?eld tuning of Whispering Gallery Mode resonances in microdroplets of a dye-doped ferroelectric liquid crystal suspended in highly transparent ?uorinated polymer solution CYTOP. The ferroelectric liquid crystal is a 9:1 mixture of CE3 and CE14 ferroelectric liquid crystals, exhibiting the ferroelectric Sm C* phase between 42°C and 74°C with a rather short helical pitch of 300 to 500 nm. In the Sm C* phase, the droplets show excellent optical homogeneity with perpendicular anchoring of liquid crystal molecules at the surface. Upon the excitation with a pulsed laser, the ferroelectric liquid crystal microdroplets emit laser light showing multimode WGM spectrum. When an external slowly varying electric ?eld is applied along the direction of the excitation laser beam, we observe a red-shift of the WGM resonances, indicating an e?ective increase of the optical path for WGM resonant light. The shift is fully reversible, it is quadratic in the applied electric ?eld and has a value of , 4.5 nm at an electric ?eld of 2 VeμmT(cid:2)1. It is qualitatively explained by considering the soliton-like deformation of the helical ferroelectric Sm C* structure in an external electric ?eld.
关键词： liquid crystals,laser sensors,lasers,tuneable,Microcavities
更新于2025-09-12 10:27:22
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Acid mediated tunability of stimulated laser emission from dye doped chiral microdroplets
摘要： In the last decade, the possibility to use liquid crystal droplets as optical micro-cavities and lasers has attracted much attention since it paves the way for many applications in the field of sensors or tunable photonics. Several techniques can be used to obtain small micro-resonators as, for example, dispersing a cholesteric liquid crystal inside an immiscible isotropic fluid to create an emulsion. Since liquid crystals are extremely sensitive to external factors as temperature or external fields, laser tuning can be easily achieved. Here, we report on the possibility to tune the laser emission from dye doped cholesteric liquid crystals microdroplets dispersed in a glycerol matrix in presence of nitric acid molecules in the emulsion. Using a fluorescent dye with pH dependent optical properties, the emitted laser wavelength can be tuned in a range of 60 nm. This effect could find applications for the development of spectroscopy based sensors.
关键词： Microdroplets,dyes,cholesteric liquid crystals,laser tuning,solvatochromism
更新于2025-09-12 10:27:22