Optical Tilt Angle Research Articles

Study of A Ferroelectric Liquid Crystal Mesogen by Geometrical Optimization and Electro-Optic Characterization

In the present work one biphenyl benzoate cored liquid crystal was characterized using geometrical optimization and electro-optic study. Geometry of the molecule was optimized using Hartree-Fock method with 3-21G basis. The simulated value of molecular length and dipole moment was reported. The Infrared (IR) spectra were also simulated and analyzed. The energy gap between highest occupied molecular orbit (HOMO) and lowest unoccupied molecular orbit (LUMO) was calculated. The phase transition temperatures and phase sequences were identified by observing the topological defects in the optical textures at different temperatures under polarizing microscope. It exhibited ferroelectric smectics C* (SmC*) phase for a wide range of temperature and then directly melted into isotropic phase. The optical tilt angle of the compound was measured in SmC* phase and was fitted with mean field model to explore the nature of phase transition. The applicability of the compound for display applications were judged based on the parameters measured.

Artificial intelligence to distinguish retinal vein occlusion patients using color fundus photographs.

Our aim is to establish an AI model for distinguishing color fundus photographs (CFP) of RVO patients from normal individuals. The training dataset included 2013 CFP from fellow eyes of RVO patients and 8536 age- and gender-matched normal CFP. Model performance was assessed in two independent testing datasets. We evaluated the performance of the AI model using the area under the receiver operating characteristic curve (AUC), accuracy, precision, specificity, sensitivity, and confusion matrices. We further explained the probable clinical relevance of the AI by extracting and comparing features of the retinal images. Our model achieved an average AUC was 0.9866 (95% CI: 0.9805-0.9918), accuracy was 0.9534 (95% CI: 0.9421-0.9639), precision was 0.9123 (95% CI: 0.8784-9453), specificity was 0.9810 (95% CI: 0.9729-0.9884), and sensitivity was 0.8367 (95% CI: 0.7953-0.8756) for identifying fundus images of RVO patients in training dataset. In independent external datasets 1, the AUC of the RVO group was 0.8102 (95% CI: 0.7979-0.8226), the accuracy of 0.7752 (95% CI: 0.7633-0.7875), the precision of 0.7041 (95% CI: 0.6873-0.7211), specificity of 0.6499 (95% CI: 0.6305-0.6679) and sensitivity of 0.9124 (95% CI: 0.9004-0.9241) for RVO group. There were significant differences in retinal arteriovenous ratio, optic cup to optic disc ratio, and optic disc tilt angle (p = 0.001, p = 0.0001, and p = 0.0001, respectively) between the two groups in training dataset. We trained an AI model to classify color fundus photographs of RVO patients with stable performance both in internal and external datasets. This may be of great importance for risk prediction in patients with retinal venous occlusion.

AlScN Piezoelectric MEMS Mirrors with Large Field of View for LiDAR Application.

This paper presents AlScN piezoelectric two-axis MEMS mirrors with gimbal-less and gimbaled designs fabricated in a CMOS-compatible manner. Integrated piezoelectric sensors provided feedback signals of the actual mirror positions. The mirror with a diameter of 1.5 mm possessed adjustable optical tilt angles of up to 22.6° @ 30 V, with a high resonance frequency of about 8.2 kHz, while the 3 mm mirror reached 48.5° @ 41 V. The mirror with the gimbaled structure exhibited an excellent field of view and good mechanical decoupling. Additionally, a significant improvement in mirror scanning performance was observed in a vacuum (4 Pa), proving that the optical field of view was magnified by more than a factor of 10.

Gamma-radiation exposure-induced modifications in the thermal, dielectric, and electro-optical properties of two-room temperature antiferroelectric liquid crystal mixtures

ABSTRACT The influence of different doses of gamma radiation on the phase transition temperatures, permittivity, conductivity, tilt angle, anchoring energy coefficients, spontaneous polarisation, rotational viscosity, and switching time of two-room temperature antiferroelectric liquid crystal (AFLC) mixtures has been investigated. At low radiation exposure, phase transition temperatures and optical tilt angles of the systems decrease slightly, but the effect is significant at high radiation doses. The permittivities as well as the ac and dc conductivities of the mixtures were significantly altered by γ-irradiation. Anchoring energy coefficients, spontaneous polarisation, rotational viscosity and switching time of the mixtures are shown to have a similar type of behaviour in both mixtures at low radiation doses, but their behaviour becomes random at higher levels of γ-irradiation.

Quantification of an oval optic disc in relation to myopic foveoschisis using swept-source optical coherence tomography

BackgroundTo investigate the relationship between an oval optic disc and the occurrence of myopic foveoschisis (MF) using swept-source optic coherence tomography (SS-OCT).MethodsFifty eyes of 25 patients with unilateral MF were included in this retrospective observational study. The biometric features of the optic disc and peripapillary structures were evaluated using SS-OCT.ResultsThe ovality index (OI) of the optic disc was significantly smaller (P = 0.003) and the optic disc tilt angle was greater (P = 0.023) in the eyes with MF than in the contralateral eyes. The optic disc tilt angle was significantly correlated with the OI (P = 0.000). Generalized estimating equation (GEE) model (linear regression) demonstrated that spherical equivalent refraction (P = 0.001), narrow macular staphyloma (P = 0.001) and the occurrence of MF (P = 0.026) were the independent factors associated with the OI. Narrow macular staphyloma was more frequent (P = 0.020) and the staphyloma was deeper (P = 0.006) in eyes with MF. GEE model (logistic regression) revealed that narrow macular staphyloma was the only independent factor related to the occurrence of MF (P = 0.013).ConclusionsAn oval optic disc in eyes with MF resulted from the increased tilt around the vertical disc axis. The optic disc tilt was related to narrow macular staphyloma, which was the only independent factor associated with the occurrence of MF. The clinical relevance needs further exploration through longitudinal analysis.

The influence of axial myopia on optic disc characteristics of glaucoma eyes

This study characterizes differences in glaucomatous eyes with and without high axial myopia using custom automated analysis of OCT images. 452 eyes of 277 glaucoma patients were stratified into non (n = 145 eyes), mild (n = 214 eyes), and high axial myopia (axial length (AL) > 26 mm, n = 93 eyes). Optic disc ovality index, tilt and rotation angle of Bruch´s membrane opening (BMO) and peripapillary choroidal thickness (PCT) were calculated using automated and deep learning strategies. High myopic optic discs were more oval and had larger BMO tilt than mild and non-myopic discs (both p < 0.001). Mean PCT was thinnest in high myopic eyes followed by mild and non-myopic eyes (p < 0.001). BMO rotation angle, global retinal nerve fiber layer (RNFL) thickness and BMO-minimum rim width (MRW) were similar among groups. Temporal RNFL was thicker and supranasal BMO-MRW was thinner in high myopic eyes. BMO tilt and PCT showed moderate and temporal RNFL and nasal BMO-MRW showed weak but significant associations with AL in multivariable analyses (all p < 0.05). Large BMO tilt angle and thin PCT are characteristics of highly myopic discs and were not associated with severity of glaucoma. Caution should be exercised when using sectoral BMO-MRW and RNFL thickness for glaucoma management decisions in myopic eyes.

Effect of γ-irradiation on various important physical properties of a room temperature ferroelectric liquid crystal mixture and its silver nanocomposite

A room temperature ferroelectric liquid crystal (FLC) mixture and its silver nanocomposite have been irradiated by various doses of γ-radiation from 60Co. Phase transition temperatures, dielectric permittivity, optical tilt angle, spontaneous polarization, rotational viscosity, switching time, and conductivity of the systems have been determined as a function of the irradiation dose and temperature. Phase transition temperatures and optical tilt angles of both the systems decrease significantly, more in the pristine mixture, meaning a decrease of the order parameter with irradiation. Remarkable changes are exhibited in the dielectric permittivity as well as in their molecular dynamics as confirmed by the change in Goldstone and soft mode relaxation frequencies. The conductivity of the irradiated mixture increases considerably compared to its nanocomposite probably due to the production of more ions by the radiolysis process. Spontaneous polarization, rotational viscosity, and switching time are also found to decrease linearly with irradiation dose. At the maximum absorbed dose, switching time decreases by 140 μs in the pristine mixture and 110 μs in the nanocomposite suggesting their more suitability in display applications. The concentration of the chiral dopant also influences the impact of irradiation.

Investigation of the tilt angle and spontaneous polarisation of antiferroelectric liquid crystals with a chiral centre based on (S)-(+)-3-octanol

The electro-optical properties (tilt angle of the director and spontaneous polarisation) of eight smectic liquid crystalline compounds with a chiral centre based on (S)-(+)-3-octanol and different substitution of the benzene ring and different length of the oligomethylene spacer (−(CH2)nO−) were studied. The compounds possess the self-assembling behaviour with an antiferroelectric ordering in smectic Ca* phase at a broad temperature range, some of materials have also a ferroelectric smectic C* phase and/or an orthogonal smectic A* phase. Due to high chemical stability and very high values of the optical tilt angle (40–44°) at saturation, the tested compounds can be used as chiral components for orthoconic antiferroelectric liquid crystalline mixtures.

Effect of γ-irradiation on the display parameters of a room temperature ferroelectric liquid crystal mixture

ABSTRACT A room temperature ferroelectric liquid crystal (FLC) mixture has been studied by irradiating with γ-radiation from 60Co source. Important display parameters such as dielectric permittivity, conductivity, spontaneous polarisation, optical tilt angle, rotational viscosity and switching time have been determined as a function of the irradiation dose. Study reveals that transition temperatures involving different phases and optical tilt angle decrease significantly, more at higher doses, which means irradiation decreases the order parameter in different phases. Conductivity increases twelve times probably due to the production of ions or impurities by radiolysis process. Irradiation also affects the dynamics of the molecules manifested by the change in critical frequencies of relaxation modes. Changes in other electro-optic properties suggest that degradation of display quality may not be significant at low γ-radiation exposure but the effect will be severe at high dose.

Dielectric and electro-optical studies of Au/SnO2 core/shell nanocrystals incorporated ferroelectric liquid crystal

ABSTRACT We study the effect of Au/SnO2 core/shell nanocrystals (NCs) on dielectric and electro-optical parameters of a ferroelectric liquid crystal (FLC) material, namely KCFLC 7S. The FLC composites are characterised through polarising optical microscope (POM), photoluminescence (PL) spectroscopy and dielectric spectroscopy. Incorporation of Au/SnO2 NCs enhances the optical contrast, optical tilt angle, PL intensity and reduces saturation voltage of a FLC mixture. This modification in electrical and optical properties is attributed to change in dynamics of FLC molecules in presence of the NCs. Dielectric measurement shows that chiral Smectic C (SmC*) phase of FLC is dominated by an applied oscillating field dependent partially unwound helical mode (p-UHM) process in FLC composite with Au/SnO2 NCs. These results would be useful to fabricate power efficient and highly luminescent NCs-FLC-based electro-optical devices.

Enhancement in electro-optical properties of ferroelectric liquid crystal by doping perovskite CsPbBr3 quantum dots

ABSTRACT We demonstrate enhancement in electro-optical properties of ferroelectric liquid crystal (FLC) material on incorporation of perovskite CsPbBr3 quantum dots (QDs). The underlying mechanism for enhancement in optical contrast, optical tilt angle, photoluminescence intensity and reduced saturation voltage of an FLC mixture is a consequence of incorporation of CsPbBr3 QDs. The amount of CsPbBr3 QDs in FLC material was varied as well. The experimental findings were attributed to the modification in the local ordering and orientation of the FLC molecules influenced by the presence of the QDs. Stable and improved electro-optical properties of FLC composite, by choosing an optimised concentration of the QDs in FLC is the primary finding of the present efforts. The results presented here are useful in the manufacturing of improved LC display devices based on QDs having larger viewing angles, improved contrast and lower operating voltage.

Effect of non-mesogenic chiral terphenylate on the formulation of room temperature ferroelectric liquid crystal mixtures suitable for display applications

By varying the concentration of a chiral terphenylate dopant in a four-component achiral phenyl pyrimidine-based host mixture we have formulated six ferroelectric liquid crystal mixtures. Though the dopant is non-mesogenic it is observed that only 2 wt% of it induces polarity in the host mixture at 32 °C. With increasing concentration, the mixtures show ferroelectric behavior even below ambient temperature down to at least 12 °C. Optical polarizing microscopy, differential scanning calorimetry, dielectric and electro-optic studies reveal that with respect to temperature range, phase sequence, spontaneous polarization, optical tilt angle and switching time the formulated mixtures are suitable for ferroelectric based liquid crystal displays.

An effect of chiral dopants on mesomorphic and electro-optical properties of ferroelectric smectic mixture

ABSTRACTThe aim of the presented research was an assessment of an effect of chiral dopants on the physical and electro-optical properties of a ferroelectric smectic mixture which is a key factor of elaboration of working ferroelectric liquid crystal (FLC) mixtures of tailored properties, especially with the tilt angle value near 22.5° in a broad temperature range. Testing FLC mixtures were prepared using the common pyrimidine-based parent mixture F4 doped with three different chiral dopants. The thermal characteristic of the optical tilt angle , tilt angle calculated by means of X-ray diffraction method , spontaneous polarisation and layer spacing of obtained FLC mixtures were studied. Based on the above measurements and computer calculations, the relationship between spontaneous polarisation and tilt angle was discussed. Electro-optical performance of the Surface Stabilised Ferroelectric Liquid Crystal (SSFLC) structures was observed. The relation between the molecular properties of chiral dopants and the electro-optical and physical properties of obtained FLC mixtures is considered in frames of the extended microscopic model of the spontaneous polarisation in FLCs.

A modified Langevin-Debye model for investigating the electro-optic behaviour of de Vries smectic liquid crystals

ABSTRACTAn external electric field applied across a planar-aligned cell in Smectic A* phase of de Vries smectic liquid crystal induces director redistribution over a cone, resulting in a substantial increase in the birefringence and the apparent optical tilt angle. Such an electro-optic response is modelled by Shen et al. [Y. Shen et al., Phys. Rev. E 88, 062504 (2013)], who modified their previous hollow cone with a diffuse cone model by introducing the molecular distribution function limited over a range of tilt angles, that lie in between θmin and θmax. The limits in these two tilt angles are assumed to be temperature independent though the tilt angle in between the two values can be temperature dependent. However, the high resolution measurements of birefringence and the layer thickness indicate the presence of temperature dependent diffuse cone angle in SmA* phase.. In the proposed model, we replace θmin by θT, a temperature dependent fitting parameter and the change shows that a better fit of the experimental data to the model is obtained. We determine the temperature dependence of θmin and show that this angle increases as SmA* to SmC* phase transition temperature is approached.

Influence of ZnO nanoparticles on the polarization, dielectric and electro-optic behaviour in the smectic C* and hexatic I* phases

Here we report the results of the dielectric and polarization measurements in the smectic and the tilted hexatic phases of a liquid crystal-nano composite consisting of commercially available ferroelectric liquid crystal (FLC) doped with the ZnO nanoparticles (NPs). It has been observed that the inclusion of NPs not only decreases in the transition temperature but also dielectric strength of the Goldstone mode without altering the associated relaxation frequency. An additional relaxation observed for the FLC-ZnO nanocomposite, but not present in the pure material is attributed to the manifestation of the primary director mode. The observed results are analyzed using the generalized Landau model to understand the effect of the coupling between the polarization and optical tilt angle. While there is no change in either the magnitude of the tilt or the polarization across the orthogonal to tilted smectic phase transitions, clear changes are seen for both the parameter across the transition to the hexatic phase. The FLC-ZnO nanocomposite exhibits decreased rotational viscosity and a faster response time, a feature attractive from an application point of view.

Design of liquid crystals with ‘de Vries-like’ properties: the effect of an ethynyl spacer in the core structure

ABSTRACTWe investigate the origins of ‘de Vries-like’ liquid crystalline behaviour by introducing an ethynyl spacer in the core of the tricarbosilane-terminated 5-phenylpyrimidine mesogens QL16-6 and QL17-6. The rationale for this structural change is based on the assumption that an ethynyl spacer would create more free volume in the core sub-layer and therefore decrease the orientational order parameter S2 in the SmA phase. The tricarbosilane-terminated mesogens WL41-5 and WL42-6 with a 5-(phenylethynyl)pyrimidine core in either a normal or inverted orientation were synthesised, and their mesomorphic and ‘de Vries-like’ properties characterised using polarised optical microscopy, differential scanning calorimetry, birefringence measurements, small–angle (SAXS) and 2D X-ray scattering. Reduction factors R derived from SAXS and optical tilt angle measurements suggest that neither WL41-5 (R = 0.49) nor WL42-6 (R = 0.80) exhibit ‘de Vries-like’ properties. The S2(T) profiles show an increase in orientational order with decreasing temperature and a sharp discontinuity at the SmA-SmC transition, which is consistent with ‘de Vries-like’ behaviour. However, the Leff(T) profiles suggest an increase in interdigitation that reduces the positive effect of increasing S2 in compensating for the molecular tilt.

Multi-channel and multi-polarization radar measurements around the NEEM site

Abstract. Ice properties inferred from multi-polarization measurements, such as birefringence and crystal orientation fabric (COF), can provide insight into ice strain, viscosity, and ice flow. In 2008, the Center for Remote Sensing of Ice Sheets (CReSIS) used a ground-based VHF (very high frequency) radar to take multi-channel and multi-polarization measurements around the NEEM (North Greenland Eemian Ice Drilling) site. The system operated with 30 MHz bandwidth at a center frequency of 150 MHz. This paper describes the radar system, antenna configurations, data collection, and processing and analysis of this data set. Within the framework derived from uniaxial ice crystal model, we found that ice birefringence dominates the power variation patterns of co-polarization and cross-polarization measurements in the area of 100 km2 around the ice core site. The phase shift between ordinary and extraordinary waves increases nonlinearly with depth. The ice optic axis lies in planes that are close to the vertical plane and perpendicular or parallel to the ice divide depending on depth. The ice optic axis has an average tilt angle of about 11.6° vertically, and its plane may rotate either clockwise or counterclockwise by about 10° across the 100 km2 area, and at a specific location the plane may rotate slightly counterclockwise as depth increases. Comparisons between the radar observations, simulations, and ice core fabric data are in very good agreement. We calculated the effective colatitude at different depths by using azimuth and colatitude measurements of the c axis of ice crystals. We obtained an average effective c axis tilt angle of 9.6° from the vertical axis, very comparable to the average optic axis tilt angle estimated from radar polarization measurements. The comparisons give us confidence in applying this polarimetric radio echo sounding technique to infer profiles of ice fabric in locations where there are no ice core measurements.

Study of variation in thermal width of nematic and induced smectic ordering phase of citric acid (CA) and 4-heptyloxybenzoic acid (7OBA) hydrogen bonded liquid crystal complexes

Hydrogen-bonded liquid crystals (HBLCs) have been derived from nonmesogenic citric acid (CA) and mesogenic 4-heptyloxybenzoic acid (7OBA) yielding a highly ordered smectic C (Sm C) phase along with the new smectic X (Sm X) phase which has been identified as fingerprint-type texture. Optical (polarizing optical microscopy), thermal (differential scanning calorimetry) and structural (Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy) properties are studied. A noteworthy observation is that the intermolecular H-bond (between CA and 7OBA) influences on its melting point and clearing temperature of the HBLCs which exhibits lower value than those of the individual compounds. A typical extended mesophase region has been observed in the present complex while varying the mixture ratio (1:1 to 1:3) than those of individual compounds. The change in the ratio of the mesogenic compound in the mixture alters thermal properties such as enthalpy value and thermal span width in nematic (N) region of HBLC complex. Optical tilt angle measurement of CA+7OBA in Sm C phase has been discussed to identify the molecular position in the mesophase.

Effect of lateral fluorine substitution far from the chiral center on mesomorphic behaviour of highly titled antiferroelectric (S) and (R) enantiomers

Several new liquid crystalline chiral ester enantiomers in the (S) and (R) configuration were designed and characterised. In order to tune their mesomorphic properties, the molecular core was laterally substituted by fluorine atoms in different positions on the benzene ring placed in the molecular core far from the chiral centre. All the materials possess the self-assembling behaviour, specifically the paraelectric orthogonal smectic A*, the ferroelectric tilted smectic C* and antiferroelectric tilted smectic CA* phases over a broad temperature range down to room temperature. Properties of the materials were characterised by the polarising optical microscopy, differential scanning calorimetry, electro-optics and dielectric spectroscopy. Due to high chemical stability, reasonably broad temperature ranges of polar smectic mesophases (up to 110°C) and very high values of the optical tilt angle (40–45°) at saturation, these materials can be used as chiral dopants for the multicomponent orthoconic mixture design aimed for development of advanced electro-optic and photonic devices.

Influence of Hydrogen Bond on Thermal and Phase Transitions of Binary Complex Liquid Crystals

A novel supramolecular liquid crystal (LC) is synthesized from the binary complex of 4-decyloxy benzoic acid and cholesteryl acetate. Fourier transform infrared (FTIR) spectroscopic study confirms the formation of intermolecular hydrogen bond between the mesogens. Various mesophases and corresponding textural changes in the complex are observed by comparing with its constituents through polarizing optical microscopic (POM) studies. The thermal stability factor of smectic phase for present complex is calculated. An interesting observation of present work is that investigation of extended thermal span of mesomorphic phases, decreased enthalpy, a nematic phase with a high clearing point and a low melting point. This is due to an arrangement of molecular reorientations and the development of new associations by hydrogen bonding. Optical tilt angle for smectic C phase is determined and the same is fitted to a power law.