Helicoidal distributed-feedback cavity action in a ferroelectric liquid crystal

Second-Harmonic (SH) generation was observed in homeotropically aligned ferroelectric liquid-crystal cells using fundamental light propagating along the helicoidal axis. Relatively strong SH light was observed in the helicoidal structure when the optical pitch was nearly the same as the SH-light wavelength, though, otherwise, the cancellation of the generated SH light by the helicoid results in negligibly weak SH intensity. Because the observed SH light is independent of the cell thickness, the SH light is attributed to the one generated from the surface region and the SH light generated inside the cell is confined and lost by the helicoid. This phenomenon indicates the helicoidal Distributed-FeedBack (DFB) cavity action and suggests the possibility of the helicoidal DFB laser using dye-doped ferroelectric liquid-crystal cells.     

Dielectric spectroscopy of a high-polarization ferroelectric liquid crystal

Dielectric spectroscopy investigations in the frequency range 50?Hz to 1?MHz have been carried out on a new ferroelectric liquid-crystalline material (S-(-)-4-(2-n-hexylpropionyloxy)biphenyl-4′-(3-methyl-4-decyloxy)benzoate) possessing a relatively large spontaneous polarization (P _s?～?240?nC?cm^?2) and containing a lateral methyl group on the aromatic ring of the alkoxybenzoate unit. The effect of temperature on the dielectric relaxation modes has been investigated in the SmC* and N* phases. From dielectric dispersion data, relaxation frequency and dielectric strength of all detected relaxation modes have been evaluated and discussed. A new surface-like mode of relaxation frequency ～11?kHz and dielectric strength 3.8, is seen to appear in the SmC* phase.     

X-ray study of ferroelectric liquid crystal

Measurements of X-ray scattering intensity from a ferroelectric liquid crystal are carefully carried out to clarify the mechanism of the ferroelectric phase transition. The temperature dependences of the scattering intensity and the tilt angle of the molecules in the ferroelectric smectic C phase are discussed on the base of Landau's theory.     

Measurement of 129Xe frequency shift due to Cs–129Xe collisions

Enhancement factor K0, which characterizes NMR and EPR frequency shifts for Cs-129Xe, is measured for the first time. The enhancement factor r-o was measured to be （702±41） at 80 ℃ and （653±20） at 90 ℃, using the NMR frequency shift, detected by atomic magnetometer at a low magnetic field of 100 nT. This result is useful for predicting the EPR frequency shifts for Cs and the NMR frequency shifts for 129Xe in spin-exchange cells.     

Spatial light modulators using ferroelectric liquid crystal

Basic structures and functions of optically addressed spatial light modulators (SLMs) are discussed in the context of system applications. The most important functions imposed on spatial light modulators are those of image acceptance and transducers. SLMs using ferroelectric liquid crystal (FLC) satisfy essential requirements for high levels of resolution, sensitivity and response speed. We specifically surveyed the current performance of bipolar-operational spatial light modulators (BSLMs) that sufficiently exploit the bistability of FLC to output reversibly positive and negative images and to store them. The high performance of BSLMs makes them useful for many optical applications including image processing and real-time holography.     

Confinement-induced orientational order in a ferroelectric liquid crystal containing dispersed aerosils

The study of the smectic-A to chiral smectic-C(*) phase transition of the liquid crystal S-(+)-[4-(2(')-methyl butyl) phenyl 4(')-n-octylbiphenyl-4-carboxylate] (CE8) containing dispersed hydrophilic aerosils reveals novel properties, important to understanding quenched disorder and confinement in ferroelectric liquid crystals. Smectic layer compression leads to a distribution of transition temperatures inducing smearing of the macroscopic data across the transition. A pronounced confinement-induced pretransitional tilted order is observed.     

Anchoring energy and orientational elasticity of a ferroelectric liquid crystal

The dielectric susceptibility of a helix-free ferroelectric liquid crystal layer has been experimentally and theoretically studied as a function of the layer thickness. The investigation has been performed on the inner branch of the polarization hysteresis loop, in the region of a linear dependence of the polarization on the electric field. The experimental results are explained using the notion of effective layer thickness, which involves the characteristic distance ?? over which the orienting effect of interfaces is operative. Comparison of the experimental data and theoretical results made it possible to estimate this distance as ?? = 41 ??m and evaluate the anchoring energy (W = 2.8 × 10^?3?1.1 × 10^?2 J/m²) and the intralayer elastic constant (K?? ?? 1 × 10^?8?3 × 10^?7 N).     

Optical properties of a QHQ ferroelectric liquid crystal phase modulator

A half-wave plate sandwiched between two-quarter-wave plates (a QHQ) may be used as a variable linear retarder. We describe some new features of the optical properties of such a device and present results of an experimental demonstration of a ferroelectric liquid crystal phase-only modulator based on the above principle.     

NMR chemical shifts of129Xe dissolved in liquid haloalkanes and their mixtures

Xenon-129 NMR spectra have been measured for solutions containing Xe dissolved in a variety of linear 1-haloalkanes, α, ω-dihaloalkanes, and their mixtures. The data are found to be linearly related to solvent composition expressed as volume fraction of the constituent methyl groups, methylene groups, and halogen atoms. This behavior is consistent with a model in which the large dispersion force contributions to the chemical shift of¹²⁹Xe result from pair interactions between dissolved Xe atoms and the methyl, and methylene groups, and the halogen atom, from which the solvent molecules are composed.     

An apparatus for NMR of laser polarized 129Xe on single crystal surfaces

Due to a lack of at least 2 orders of magnitude in the amount of sample nuclei, single crystal surfaces are out of reach for conventional NMR measurements. Our aim is to prove that highly polarized ¹²⁹Xe provides a technique to overcome this restriction. Therefore an apparatus for polarizing ¹²⁹Xe up to 0.7 by spin transfer from optically pumped Rb has been designed as well as an NMR spectrometer in combination with a UHV chamber with sample cleaning, cooling and characterization abilities and a special manifold of glass stopcocks with a liquid nitrogen cooled trap for dosing nitrogen free polarized Xe into the chamber onto the surface. This revised version was published online in August 2006 with corrections to the Cover Date.     

Enhancement of SQUID-detected NMR signals with hyperpolarized liquid 129Xe in a 1 microT magnetic field

We report an enhancement of proton NMR signals by a factor of 10(6) by cross polarization with hyperpolarized liquid 129Xe in an ultralow magnetic field of 1 microT. The NMR signals from cyclopentane, acetone, and methanol are detected using a commercial high-T(c) SQUID magnetometer with a signal-to-noise ratio of up to 1000 from a single 90 degrees tipping pulse. This technique allows a wide range of low-field NMR measurements and is promising for the detection of intermolecular scalar spin-spin couplings. Scalar intermolecular couplings can produce a shift of the average NMR frequency in a hyperpolarized sample even in the presence of rapid chemical exchange.     

Changes in material parameters for dye-doped ferroelectric liquid crystal

Addition of the dichroic anthraquinone dye molecules in pure ferroelectric liquid crystal (FLC) matrix results in many improvement in the various vital parameters of the pure FLC. However, addition of anthraquinone dye molecules in pure FLC matrix is not advantageous every time. There are certain constraints which are crucial for the application of these systems into many devices. In this article, we have discussed the concentration and temperature dependence of vital properties of dye-doped FLC. In this study there is improvement in contrast ratio by dye doping due to enhancement in plane switching for dye-doped FLC.     

Modelling and characterization of ferroelectric liquid crystal displays

Modelling of liquid crystal displays is useful to predict their optical properties and dynamic behaviour. An integrated modelling system for ferroelectric liquid crystal displays has been developed. The system employs data from real FLC materials, polarizers, glasses, backlights, and colour filters, aiming to describe actual devices accurately. Optical transmission dependence on light wavelength and angle of incidence is obtained as a function of the liquid crystal director profile. This profile is in turn derived from energy minimization of bulk and glass surface conditioning contributions.The above static model has been extended to study sample switching in multiplexed displays. Usual slot times in actual displays are quite close to time response of FLC materials, hence no energy-minimized configurations are obtained upon switching. A dynamic model has been formulated to derive the director profile evolution with time, according to the employed driving scheme, and the rotational viscosity of the material.Predicted dynamic and optical results have been compared to experimental measurements on FLC test cells. It has been found that the behaviour of FLC cells depends on a large number of physical and optical parameters. Some of them may be obtained from FLC data sheets, and manufacturing conditions. Other parameters related to director profiles in relaxed states may be experimentally obtained by sample characterization through optical transmission measurements. A few little known parameters (e.g. specific elastic constants) remain; fortunately their influence on cell dynamics is low.     

Measurements of absolute values of electrooptic coefficients in a ferroelectric liquid crystal

Weak external electric field E causes two effects in chiral smectic liquid crystals: linear change of the optic axis direction and modification of the shape of the indicatrix. The relative changes in the light intensity consist of two components. The first component represents the modulation with the fundamental frequency f and the second one, with the doubled frequency 2f (second harmonic). We carried out measurements of the electrooptic modulation at both the first and second harmonics frequency. The applied calibration procedure allowed for expressing the experimental results as angular quantities independent of experimental conditions. Therefore we were able to determine the absolute values of the coefficients describing both effects of the electric field on the optical properties of the sample. We studied the temperature dependence of the first and second order coefficients in the ferroelectric smectic C? and paraelectric smectic A phases. The experiments delivered an information on the structure of tilted smectic liquid crystals and its dependence on the electric field.     

Transverse spin relaxation in liquid 129Xe in the presence of large dipolar fields

Using spin-echo NMR techniques we study the transverse spin relaxation of hyperpolarized liquid 129Xe in a spherical cell. We observe an instability of the transverse magnetization due to dipolar fields produced by liquid 129Xe, and find that imperfections in the pi pulses of the spin-echo sequence suppress this instability. A simple perturbative model of this effect is in good agreement with the data. We obtain a transverse spin relaxation time of 1300 sec in liquid 129Xe, and discuss applications of hyperpolarized liquid 129Xe as a sensitive magnetic gradiometer and for a permanent electric dipole moment search.     

129Xe contact shift in oxygen gas

We have determined the temperature dependence of σ₁ of ¹²⁹Xe in oxygen gas. These results were obtained by measurement of the resonance frequency of ¹²⁹Xe in gas samples of known densities in Xe and O₂. The shift of the resonance frequency due to Xe-Xe interactions has been measured in pure Xe gas samples with improved precision. This allows the determination of σ₁(Xe-O₂) by subtracting out the known effect of Xe-Xe interactions in mixed Xe-O₂ samples. σ₁(Xe-O₂) values are reported here for the temperature range 220 to 440 K. The values of σ₁(Xe-O₂) are adequately described by the polynomial function in p.p.m. amagat^-1 σ₁(Xe-O₂) = - 1·061 + 3·64 × 10^-3τ - 2·19 × 10^-5τ² + 9·58 × 10^-8τ³ - 2·08 × 10^-10τ⁴, where τ = (T - 300 K). It is found that the temperature dependence of σ₁(Xe-O₂) can be interpreted in terms of a contact interaction between Xe and the paramagnetic O₂ molecule.     

Relaxation of hyperpolarized 129Xe in a deflating polymer bag

In magnetic resonance imaging with hyperpolarized (HP) noble gases, data is often acquired during prolonged gas delivery from a storage reservoir. However, little is known about the extent to which relaxation within the reservoir will limit the useful acquisition time. For quantitative characterization, 129Xe relaxation was studied in a bag made of polyvinyl fluoride (Tedlar). Particular emphasis was on wall relaxation, as this mechanism is expected to dominate. The HP 129Xe magnetization dynamics in the deflating bag were accurately described by a model assuming dissolution of Xe in the polymer matrix and dipolar relaxation with neighboring nuclear spins. In particular, the wall relaxation rate changed linearly with the surface-to-volume ratio and exhibited a relaxivity of κ=0.392±0.008 cm/h, which is in reasonable agreement with κ=0.331±0.051 cm/h measured in a static Tedlar bag. Estimates for the bulk gas-phase 129Xe relaxation yielded T1bulk=2.55±0.22 h, which is dominated by intrinsic Xe-Xe relaxation, with small additional contributions from magnetic field inhomogeneities and oxygen-induced relaxation. Calculations based on these findings indicate that relaxation may limit HP 129Xe experiments when slow gas delivery rates are employed as, for example, in mouse imaging or vascular infusion experiments.