Birefringence Parameters Research Articles

Conoscopic study of strontium-barium niobate single crystals

Optically transparent single crystals of strontium-barium niobate, SrxBa1-xNb2O6, of different compositions (x = 0.26...0.7) were examined with the aid of conoscopic light interference figures. A regular change of the isochrome concentric ring number and diameters consistent with the temperature variation of the value of birefringence is demonstrated by direct observations of polar cuts of optically uniaxial samples. Anomalous violations of the conventional (uniaxial) interference patterns occur occasionaly in some samples being indicative of the existence of biaxial trait in their behaviour even though no voltage is applied. These features may depend on annealing treatments at elevated temperatures. The results of the study show that conoscopic images may serve as a sensitive indicator of the structural state of SBN crystals related to the effects of stress–induced change of optical anisotropy and temperature dependent birefringence parameters.

Do quantitative birefringence characteristics of meiotic spindle and zona pellucida have an impact on implantation in single embryo transfer cycles?

The aim of this study was to determine whether quantitative PolScope characteristics of meiotic spindle and zona pellucida could be used as a non-invasive marker to predict implantation success in elective single embryo transfer cycles. Quantitative birefringence parameters; including mean retardance, area, length and polar body deviation angle of meiotic spindle and mean retardance and width of inner zona pellucida belonging to 53 transfer oocytes from elective single embryo transfer cycles were retrospectively analyzed. The relevant PolScope features were compared between 20 conception and 33 non-conception cycles. Meiotic spindle mean retardance, area, length and inner zona pellucida mean retardance and width did not reveal a statistically significant difference between transfer oocytes from conception and non-conception cycles. Deviation angle of the polar bodies was also comparable between the groups. Spindle and inner zona PolScope characteristics of transfer oocytes were not correlated with the maternal age. Quantitative PolScope features of meiotic spindle and inner zona pellucida can not be used as a non-invasive marker to predict assisted reproductive technology success in elective single embryo transfer cycles.

Anisotropic Alteration of Scleral Birefringence to Uniaxial Mechanical Strain

PurposeTo investigate the relationship between scleral mechanical properties, its birefringence, and the anisotropy of birefringence alteration in respect of the direction of the strain by using PS-OCT.MethodsThe scleral birefringence of thirty-nine porcine eyes was measured with a prototype PS-OCT. A rectangle strip of sclera with a width of 4 mm was dissected at the temporal region 5 mm apart from the optic nerve head. The strain and force were measured with a uniaxial tension tester as the sample was stretched with a speed of 1.8 mm/min after preconditioning. The birefringence of the sample was measured by PS-OCT at the center of the sample before applying, denoted as inherent birefringence, and after applying stretching of 6.5% strain. The birefringence alteration was obtained by these two measurements and correlations between birefringence and elastic parameters, tangent modulus, and structural stiffness were examined. Twenty and 19 porcine eyes were stretched in meridional or equatorial directions, respectively.ResultsA moderate positive correlation was found between the inherent birefringence and the structural stiffness. A moderate positive correlation was also found between the inherent birefringence and the tangent modulus. The birefringence increased by strains. Marginal significance was found in the birefringence alteration between meridional and equatorial strains, where the mean birefringence elevation by meridional strain was higher than that by equatorial strain.ConclusionsThe birefringence was found to be altered by applying strain and also be related with inherent birefringence. This implies the birefringence of the sclera of the in vivo eye also could be affected by its mechanical property.

Spatial-frequency polarization phasometry of biological polycrystalline networks

A model of generalized optic anisotropy of the fibrillar protein matrices has been suggested and the method of Fourier polarimetry for the parameters of linear and circular birefringence of the tissue biopsy of the uterine wall with spatial-frequency selection of such coordinate distributions for a differentiation of benign (fibromyoma) and malignant (adenocarcinoma) conditions has been substantiated. A set of criteria for a polarization-phase differentiation of benign (fibromyoma) and malignant (adenocarcinoma) conditions of the uterine has been revealed and substantiated.

The influence of structure on the elastic, optical and dielectric properties of nematic phases formed from bent-core molecules

The physical properties of the nematic phases formed by four bent-core oxadiazole based materials are reported. In particular, the splay (K11), twist (K22) and bend (K33) elastic constants, the birefringence and the dielectric anisotropy of the materials are described and the effect of chain length and the presence of fluoro-substituents at the outer phenylene group of the aromatic core structure on these parameters is determined. The birefringence and order parameter are found to be independent of the modification of molecular structure. The dielectric anisotropy is quite strongly dependent on molecular structure; the fluoro-substituted material has the largest magnitude of dielectric anisotropy while the alkyl-substituted compound has the smallest. Changes in the molecular length and fluoro-substitution in the bent-core materials are found to have little influence on the splay, twist and bend elastic constants at equivalent reduced temperatures. However, the material substituted with an alkyl terminal chain exhibits both smaller elastic constants and a less marked dependence on temperature than the alkoxy-substituted compounds. A possible insight into the behaviour of the elastic constants relevant to the formation of the dark conglomerate phase, which underlies the nematic phase in one of the compounds studied, is suggested by following the analysis proposed by Berreman and Meiboom. Importantly, using molecular field theory and atomistic modelling, we calculate elastic constants that are in excellent agreement with the experimental values. Our conclusion that the elasticity in the nematic phase formed from bent-core molecules is not strongly influenced by changes to the terminal chains or the presence of fluoro-substituents at the outer phenylene group of the aromatic core structure is in agreement with our previous work showing that the dominant parameter is the bend angle.

Order Parameters and Refractive Indices of Two Carboxylate Nematic Liquid Crystals With Negative Dielectric Anisotropy

Refractive indices of two carboxylate nematic liquid crystals have been measured throughout the nematic and isotropic phases to determine their order parameters by using the Vuks method [Vuks, M. F. (1966). Opt. Spektrosk., 20, 644], and characterization of anisotropic behaviors. These factors characterize anisotropic behaviors of selected liquid crystals with negative dielectric anisotropy that are essential for their applications and improvement. The temperature dependence of refractive indices, birefringence, and order parameters in the anisotropic phase have been investigated for these nematic liquid crystals. Furthermore, the alkyl substituents’ effects on the order parameters of carboxylate liquid crystals were also investigated.

Analytical approach for unique determination of cell parameters and equivalent birefringent parameters of a generally twisted nematic liquid crystal device

In the measurement of a twisted nematic liquid crystal device (TNLCD) by an optical apparatus, the cell parameters of the TNLCD may result in multiple solutions in the measurement that all agree with the measured data; hence manufacturers cannot find a set of correct solutions from among the ambiguous ones. With the help of the optical equivalence theorem of a unitary optical system, the ambiguity of the measured parameters of a TNLCD, including cell parameters and equivalent birefringent parameters, can be simultaneously removed by an analytical approach using a single-wavelength polarimeter. The procedure for unique determination of the cell parameters is performed using a self-consistent condition to select a set of the correct solutions from all the possible solutions. The proposed method can be applied to characterize a generally TNLCD for which the twisted angle is close to 270° and the liquid crystal phase retardation is over 2π.

Optical Defect Modes in Chiral Liquid Crystals at Birefringent Defect Layer

An analytic approach to the theory of the optical defect modes in chiral liquid crystals (CLC) for the case of a birefringent defect layer is developed. The analytic study is facilitated by the choice of the problem parameters. Namely, a birefringent layer (with the averaged dielectric susceptibility equal to the average dielectric susceptibility of CLC) sandwiched between two CLC layers inserted in an isotropic medium with the dielectric constant equal to the average dielectric constant of CLC is studied. The chosen model allows one to get rid off the polarization mixing at the external surfaces of the defect structure (DMS) and to reduce the corresponding equations to the equations for light of diffracting in CLC polarization only. The dispersion equation determining connection of the defect mode frequency with the layer birefringence and other parameters of the defect structure is obtained. Analytic expressions for the transmission and reflection coefficients of the defect mode structure (CLC- birefringent defect layer-CLC) are presented and analyzed. It is shown that generally speaking the layer birefringence reduces the DM lifetime in comparison with the DMS with an isotropic defect layer and only at discrete values of DMS parameters it achieves the value of the corresponding DMS with an isotropic defect layer. Correspondingly, generally speaking, the effect of anomalously strong light absorption at the defect mode frequency and the lowering of the lasing threshold are not so pronounced as in the case of the DMS with an isotropic defect layer. The case of DMS with low defect layer birefringence is studied in details. The options of effectively influence at the DM parameters by changing the defect layer birefringence are discussed.

Birefringence Polarimeter Using Dual LiNbO3 Electrooptic Crystal Modulators

A birefringence polarimeter that uses dual LiNbO3 electrooptic crystal modulators operating at a frequency ratio of 4:1 is described. The significance of this polarimeter is that the birefringent parameters of a sample are obtained only from the modulated polarization status. The measurement, therefore, avoids depolarization effects resulting from the sample itself and the rest of the optical system. The high speed and accuracy of this polarimeter are shown by measurements using a quarter-wave plate, a Babinet–Soleil compensator, and a phase modulator.

Order parameters and refractive indices of some cyano-benzoate nematic liquid crystals with high transition temperatures

Three cyano-benzoate liquid crystals' refractive indices have been measured throughout the nematic and isotropic phase in order to determine their order parameters by using Vuks methods and characterization of anisotropic behaviors. The temperature dependence of refractive indices, birefringence and order parameters in the anisotropic phase, has been investigated for these nematic liquid crystals. Furthermore, the alkyl substituent's effects on the order parameters of cyano-benzoate liquid crystals were investigated.

Zona pellucida birefringence correlates with developmental capacity of bovine oocytes classified by maturational environment, COC morphology and G6PDH activity

In the present study we aimed to analyse structural changes during in vitro maturation of the bovine zona pellucida (ZP) by scanning electron microscopy (SEM) ands zona pellucida birefringence (ZPB). Here we show that alterations during in vitro maturation invasively analysed by SEM are reflected in ZPB. In vivo-matured oocytes displayed significantly lower birefringence parameters and significantly higher blastocyst rates compared with in vitro-derived oocytes (39.1% vs 21.6%). The same was observed for in vitro-matured oocytes with cumulus-oocyte complex (COC) Quality 1 (Q1) compared with Q3-COCs with respect to zona birefringence and developmental capacity. Immature oocytes with Q1-COCs displayed higher ZPB values and a higher developmental capacity to the blastocyst stage (27.7% vs 16.9%) compared with immature Q3-COCs. Considering in vitro-matured oocytes, only those with Q1-COC showed a trend for ZPB similar to in vivo-matured oocytes. Therefore, a decreasing trend for ZPB during in vitro maturation seems to be typical for high-quality oocytes and successful cytoplasmic maturation. In accordance, fully-grown immature oocytes reached significantly higher blastocyst rates (32.0% vs 11.5%) and lower ZPB values compared with still-growing ones. In conclusion, we successfully evaluated the applicability of zona imaging to bovine oocytes: alterations during in vitro maturation invasively analysed by scanning electron microscopy were reflected in the birefringence of the zona pellucida of bovine oocytes affecting developmental capacity at the same value. Therefore ZPB measurement by live zona imaging has potential to become a new tool to assess correctness of in vitro maturation and to predict developmental competence.

Polychromatic intensity point spread function of a birefringent lens

We study the intensity point spread function (IPSF) of a uniaxial birefringent lens sandwiched between two linear polarizers under broadband illumination having flat-top spectral profile. The optic axis of the birefringent crystal is perpendicular to the lens axis. For monochromatic input illumination, a low-power birefringent lens offers enhanced resolution under parallel-polarizers configuration and apodization under crossed-polarizers configuration with a single focus as well. At a relatively high value of birefringence parameter, the proposed system behaves as a double-focus lens. The present communication uses a novel technique to study the effect of polychromatic illumination on the imaging characteristics of birefringent lenses. The studies reveal that the imaging characteristics of the low-power birefrigent lens does not deteriorate considerably under polychromatic illumination. However, for a polychromatic beam with large bandwidth, the imaging behavior of the system having high birefringence parameter deviates appreciably from that under strictly monochromatic illumination. The said system even loses its inherent bi-focal nature due to depolarization of polarized polychromatic light upon passage through the birefringent crystal.

Phase Transition, Birefringence and Orientational Order Parameter Studies in Four Members of Benzylidene Aniline Liquid Crystals

The nature of the phase transitions across isotropic–nematic (IN) and nematic–smectic-A (N-SmA) are carried out using density measurements in N-(p-n-ethoxy benzylidene)-p-n-pentyl aniline, 2O.5, N-(p-n-methoxy benzylidene)-p-n-pentyloxy aniline, 1O.O5, N-(p-n-ethyl benzylidene)-p-n-dodecyl aniline, 2.12 and N-(p-n-butyl benzylidene)-p-n-dodecyl aniline, 4.12. The compounds exhibit IN, IN, IN and INSmA phase sequences respectively with varying thermal ranges suitable for the study of birefringence. The birefringence studies are carried out using Newton’s rings and wedge techniques which provide δn = (ne- no) (the birefringence) ne, and norespectively. The orientational order parameter, S is evaluated (i) directly from δn and Δn (the birefringence in perfect order), independent of the local field that the nematic molecule experiences and (ii) from molecular polarizabilities estimated from ne, noand density values assuming isotropic as well as anisotropic field that the nematic molecule experiences. The estimated order parameter from the different techniques is compared with one another and with the literature data.

Effects of glow-discharge nitrogen-plasma on the linear birefringence of polyester sheets

A simple white light interferometric method is used to study the effects of plasma on the steady-state linear birefringence of polyester sheet films. Glow-discharge nitrogen-plasma of power 13 W with nine different exposure times from 0 to 25 min is applied to films of 0.22 mm thickness. The relationship between the linear birefringence and some atomic parameters is derived theoretically and tested experimentally. Effects on the linear birefringence, the linear retardance and Herman's orientation parameter are investigated. The increase of plasma exposure time produces an increase in the linear birefringence and Herman's orientation parameter. Characterization of plasma-treated and plasma-untreated polyester samples have been thoroughly examined using Fourier transform infrared (FTIR) spectroscopy. It is noted that no new bands have appeared after treatment for all the tested samples at different time intervals. There is an increase in intensity and band definition, and a shift of some bands that were already present in the spectrum of the untreated sample, assigned to the trans conformer.

High Birefringence Photonic Crystal Fibers

Photonic crystal fiber (PCFs) offer new possibilities of realizing highly birefringence fibers due to a higher intrinsic index contrast compared to conventional fibers. Here, based on general section structure of PCFs, we take some mend in the core configuration, and achieve highly birefringence effect. A elliptic air hole and its inscribed circular high refractive material form the core of PCFs together. Especially to mention, they are being tangent at two points. By optimally selecting parameters, the effective refractive index difference between two orthogonal directions neff can reach the magnitude of 10-2. After numerical calculation, we find that increase the size of circular solid core, or long axe size of elliptic air hole, birefringence parameter of modal field can become more highly. Moreover, by matching structure parameters appropriately, the modal field diameters can be equivalent in the two orthogonal directions. A Gaussian modal field with highly birefringence character can be acquired.

Refractive indices and order parameters of some tolane-based nematic liquid crystals

Four tolane-based liquid crystals, 4′-pentyl-, 4′-hexyl-, and 4′-heptyl-3-fluoro-4-isothiocyanatotolane and 4′-hexyloxy-3′-fluoro-4-isothiocyanatotolane have been investigated throughout the nematic and isotropic phase in order to determine their refractive indices and order parameters using the Vuks method. These factors characterize anisotropic behaviors of selected liquid crystals that are essential for their applications and improvement. The temperature dependence of refractive indices, birefringence and order parameters in anisotropic nematic phase, have been investigated for these four nematic liquid crystals. All the compounds have positive and large optical anisotropies that increase with decreasing temperature.

Birefringence parameter available for quantitative analysis of human zona hardness

This study was designed to investigate whether a non-invasive birefringence parameter, determined using the Oosight™ imaging system, is useful for estimating the hardness of human zona pellucida (ZP). The value for retardance (R) × thickness (T), but not R or T alone, of ZP was positively correlated (r = 0.92, p < 0.0001) with its hardness estimated by the time required for a 0.1% protease solution to solubilize ZP at 37 °C. In a model experiment to induce ZP puncture by Fluorinert™ fluid microinjection (sham-hatching), the R × T value at the punctured site was positively correlated (r = 0.78, p < 0.01) with the hardness of the ZP as estimated by the maximum expansion rate. The R × T values of ZP in in vitro fertilization-derived embryos (21.6 ± 7.5) and intracytoplasmic sperm injection-derived embryos (20.8 ± 6.3) were significantly higher than that in unfertilized metaphase II oocytes (16.6 ± 6.1; p < 0.05). The R × T value after in vitro hatching of viable blastocysts (10.8 ± 6.2) was significantly lower than that of unexpanded morulae and early blastocysts (19.0 ± 4.0; p < 0.05), while the value of expanding blastocysts (15.3 ± 4.1) was intermediate. In conclusion, hardness of human ZP can be estimated non-invasively by birefringence-based microscopic observation.

Measurements of linearly birefringent media parameters using the optical vortex interferometer with the Wollaston compensator

The classical Mach?Zehnder two-beam set-up has been modernized with the use of polarization elements to generate a set of optical vortices. The main element of these set-ups is the Wollaston compensator, which allows us to obtain a specific phase distribution (with polarization singularities) in one of the arms of our interferometer. We have confirmed the practical value of this set-up by developing a method of birefringent media properties measurement. In the present paper we have started with developing the method for linearly birefringent media only: however, we hope that this method can be extended to elliptically birefringent media. The numerical analysis has confirmed our theoretical predictions. The mutual displacement measurements of the two OV sublattices of different topological charges allowed us to calculate the basic birefringent media parameters: the azimuth angle of its first eigenvector and the phase difference between their eigenwaves. We also carried out some experiments which convinced us about the practical value of the proposed set-ups.

Dynamic polarization states and birefringence distributions measurements in spatial elliptical polariscope using Fourier analysis method

A new method to measure the light polarization state and the birefringent media parameters is proposed. We have used the setup described previously, consisting of two pairs of the linear Wollaston and circular compensators which form a set of two spatially modulated elliptical compensators. We have modified this setup introducing some carrier frequencies in all compensators and assuming that the second linear one would introduce the frequency which is a multiplicity of the basis frequency of the first linear compensator. Both of these modifications allow calculating all polarization parameters of polarized light or birefringent medium from only one measured intensity distribution of the light outcoming the described setup. They allow measuring not only the parameters of homogeneous beams/mediums but also x,y-distributions of all desired parameters, like azimuth and ellipticity angles of the light or first medium eigenvector and the phase difference introduced by this medium. The proposed calculation method comprises of Fourier analysis of obtained intensity distribution with some manipulation of coordinate system and filtration of obtained data. This method is claimed to be simple and fast enough to be treated as a real-time method.

Vector analysis of stimulated Brillouin scattering amplification in standard single-mode fibers

The polarization properties of stimulated Brillouin scattering (SBS) amplification or attenuation in standard single-mode fibers are examined through vectorial analysis, simulation and experiment. Vector propagation equations for the signal wave, incorporating SBS and birefringence, are derived and analyzed in both the Jones and Stokes spaces. The analysis shows that in the undepleted pump regime, the fiber may be regarded as a polarization-dependent gain (or loss) medium, having two orthogonal input SOPs, and corresponding two orthogonal output SOPs, for the signal, which, respectively, provide the signal with maximum and minimum SBS amplification (or attenuation). Under high Brillouin gain conditions and excluding zero-probability cases, the output SOP of arbitrarily polarized input signals, would tend to converge towards that of maximum SBS gain. In the case of high SBS attenuation the output SOP of an arbitrarily polarized signal would approach the output SOP corresponding to minimum attenuation. It is found that for a wide range of practical pump powers ( < or = 100mW) and for sufficiently long fibers with typical SBS and birefringence parameters, the signal aligned for maximum SBS interaction will enter/emerge from the fiber with its electric field closely tracing the same ellipse in space as that of the pump at the corresponding side of the fiber, albeit with the opposite sense of rotation. The analytic predictions are experimentally demonstrated for both Stokes (amplification) and anti-Stokes (attenuation) signals.