Birefringence Imaging Research Articles

Structural and optical study of the phase transitions in Lead Hafnate, PbHfO3

Lead Hafnate undergoes two structural phase transitions as a function of temperature. The first occurs at about 1630C, consisting of a transition from an antiferroelectric orthorhombic Pbam structure [1] to another antiferroelectric orthorhombic phase with an as-yet undetermined space group. The second is to a paraelectric cubic Pm3m structure at 2090C. Dielectric spectroscopy measurements on a single crystal have shown a distinct temperature hysteresis at the orthorhombic to orthorhombic transition [2]. Recently, dielectric measurements on a ceramic sample have shown a much larger temperature hysteresis and following x-ray diffraction measurements, it is suggested that the second orthorhombic phase is in space group A2mm and undergoes another transition to a tetragonal P4mm structure before the cubic transition [3]. We report on the results of an investigation of a PbHfO3crystal using a combination of high-resolution x-ray diffraction and birefringence imaging measurements with the Metripol system. These measurements have been performed as a function of temperature from the room-temperature orthorhombic structure to the high-temperature cubic structure. The results are discussed both in the context of the published work and fundamental understanding of the origin of antiferroelectricity.

Evaluation method for grown-in dislocations in CVD single crystal diamond using plasma surface treatment

Etch pits were formed on the surface of a freestanding CVD homoepitaxial (001)-oriented diamond film using an oxygen and hydrogen (O/H) plasma. Nomarski images of the film surface after such plasma treatment and transmission birefringence images with butterfly-shaped strain patterns induced by dislocations in the film were compared. The obtained results suggested that each etch pit individually corresponds to each threading dislocation line. The number of dislocation lines in the grown-in dislocation bundle in the CVD diamond was evaluated by counting the number of etch pits aggregating around the dislocation bundle.

X-ray birefringence imaging.

The polarizing optical microscope has been used since the 19th century to study the structural anisotropy of materials, based on the phenomenon of optical birefringence. In contrast, the phenomenon of x-ray birefringence has been demonstrated only recently and has been shown to be a sensitive probe of the orientational properties of individual molecules and/or bonds in anisotropic solids. Here, we report a technique-x-ray birefringence imaging (XBI)-that enables spatially resolved mapping of x-ray birefringence of materials, representing the x-ray analog of the polarizing optical microscope. Our results demonstrate the utility and potential of XBI as a sensitive technique for imaging the local orientational properties of anisotropic materials, including characterization of changes in molecular orientational ordering associated with solid-state phase transitions and identification of the size, spatial distribution, and temperature dependence of domain structures.

Haemozoin Detection in Mouse Liver Histology Using Simple Polarized Light Microscope

The presence of malarial pigment (haemozoin) due to Plasmodium infection is a common histopathological effect in mouse liver. Previous research showed that by using a polarized light microscope, researchers were better able to detect haemozoin in mouse liver histology section. Thus, the aim of this research was to compare the haemozoin area observed by a conventional vs. simple polarized light microscope by using image processing analysis. A total of 40 images produced from both conventional light microscope and simple polarized light microscope were collected. All images were analyzed using ImageJ 1.47 software to measure the haemozoin areas. Our results showed that non birefringent haemozoin and birefringent haemozoin area was significantly different. This was because when using conventional light microscope the brown area that contained images of non birefringent haemozoin images also contained Kupffer cells which appeared as the same brown color as haemozoin. In contrast, haemozoin gave bright effect and can be easily differentiated with Kupffer cells in the birefringent haemozoin images. This study concluded that haemozoin detection in mouse liver histology using a simple polarized light microscope was more accurate compared to that of conventional light microscope.

Effect of Intraocular Pressure and Anisotropy on the Optical Properties of the Cornea: A Study Using Polarization Sensitive Optical Coherence Tomography.

We hypothesize that because of the anisotropic properties of the cornea, there should be a nonuniform change in birefringence with an increase in intraocular pressure (IOP). In this in vitro study, anisotropic properties, stress distribution within the cornea, and the effect of IOP on changes in stress level were investigated. Button inflation tests for deformation with polarization sensitive optical coherence tomography were used to demonstrate optical and material anisotropy on ex vivo human corneas. Inflation tests were performed on human donor corneoscleral rims. Using a turntable and hydrostatic column, each corneoscleral rim was subjected to a hydrostatic pressure of 0, 10, 15, and 20 mm Hg. At each pressure step, 4 scans at 0, 45, 90, and 135 degrees were taken by a polarization sensitive optical coherence tomography system, and the birefringence images and normal intensity-based images were recorded; images were later compiled for analysis. The retardation changed with the axis of orientation (P [T ≤ t] 1-tailed = 0.025) and IOP (P [T ≤ t] 1-tailed = 0.019). Optical thickness of the cornea decreased with increasing IOP. The optical properties of the cornea are modified with change in IOP. This is not uniform because of distinct anisotropic properties. Anisotropic properties may unpredictably affect the optical quality of cornea during or after the surgeries. Changes in corneal birefringence can be also used as a tool for measuring the IOP of the eye.

Capillary-Force-Assisted Self-Assembly (CAS) of Highly Ordered and Anisotropic Graphene-Based Thin Films

We report capillary-force-assisted self-assembly (CAS) as a method for preparation of thin films of chemically reduced graphene oxide (rGO) with unidirectional organization of rGO sheets. The films were initiated at the contact line of the air–liquid–solid interface and form directly on solid substrates dipped in an isotropic colloidal suspension of rGO. Assisted by capillary forces at the contact line, the suspension undergoes an isotropic-to-anisotropic phase transition and becomes aligned with the film growth direction as the contact line moves across the substrate surface. We determined the degree of order in rGO films and assemblies by birefringence and diattenuation imaging. The slow axis of the rGO platelets within the CAS films displayed a narrow angular distribution (±3°) within a film area of 1 mm2, resulting in the highest possible order parameter (S) of ∼1 with 8-fold enhancement of electrical conductivity compared to films formed by traditional techniques such as filtration. Our straightforward film fabrication technique is scalable to produce large areas of films, and by controlling the rates of convective to diffusive mass transport, films with varying degree of order can be produced.

Substrate crystal recovery for homoepitaxial diamond synthesis

Abstract Homoepitaxial chemical vapor deposition (CVD) of diamond requires high quality substrate crystals. This paper describes the process of diamond substrate crystal recovery so that the original substrate can be reused for multiple synthesis processes. A three-stage treatment is applied after homoepitaxial CVD growth. First the original substrate is separated by laser cutting, then the cut surface is mechanically polished, and finally polycrystalline material at the edges of the recovered seed plate is laser trimmed. This recovery process yields reusable diamond substrates that do not differ appreciably from their original state in terms of stresses and impurity concentrations. While the recovery process was demonstrated using HPHT seed substrates the process can also be applied to the as-grown CVD diamond plates. Infrared absorption spectral analysis, surface profilometry, birefringence imaging and Raman spectroscopy are performed after each processing step to monitor crystal quality. The nitrogen concentration in the substrate crystal remains constant throughout CVD and recovery processes. When using HPHT type Ib substrates the detected nitrogen concentration is 110–180 ppm. The nitrogen is mainly incorporated in form of C center defects and no transformation to other forms of defect centers occurs during the CVD process. Birefringence imaging showed a low level of internal stress within the HPHT crystals. No change is observed during CVD growth and recovery processes. It is shown that the polycrystalline rim removal is essential for repeatable CVD deposition on the same seed substrate. Substrate crystal recovery allows growth of up to 20 crystals from one original seed.

Polarized light imaging of birefringence and diattenuation at high resolution and high sensitivity

Polarized light microscopy provides unique opportunities for analyzing the molecular order in man-made and natural materials, including biological structures inside living cells, tissues, and whole organisms. 20 years ago, the LC-PolScope was introduced as a modern version of the traditional polarizing microscope enhanced by liquid crystal devices for the control of polarization, and by electronic imaging and digital image processing for fast and comprehensive image acquisition and analysis. The LC-PolScope is commonly used for birefringence imaging, analyzing the spatial and temporal variations of the differential phase delay in ordered and transparent materials. Here we describe an alternative use of the LC-PolScope for imaging the polarization dependent transmittance of dichroic materials. We explain the minor changes needed to convert the instrument between the two imaging modes, discuss the relationship between the quantities measured with each instrument, and touch on the physical connection between refractive index, birefringence, transmittance, diattenuation, and dichroism.

Birefringence imaging and orientation of laser patterned β-BaB2O4 crystals with bending and curved shapes in glass

Abstract Nonlinear optical β-BaB 2 O 4 crystals (β-BBO) with bending and curved shapes were patterned at the surface of 8Sm 2 O 3 –42BaO–50B 2 O 3 glass by laser irradiations (Yb:YVO 4 laser with a wavelength of 1080 nm, power of 0.8 W, and scanning speed of 4 μm/s), and the orientation state of β-BBO crystals was examined from the birefringence imaging obtained by polarization optical microscope (POM) observations. The formation (crystallization) of β-BBO crystals follows along laser scanning direction even if the laser scanning direction changes at a certain point within the bending angle of 60°. The birefringence images indicate that the formation of highly c -axis oriented β-BBO crystals follows along laser scanning direction even if the laser scanning direction changes, and in particular the direction of the c -axis of β-BBO crystals changes gradually at the bending point. The model for the orientation of the c -axis of β-BBO near the bending point is proposed. The present study proposes that the laser-induced crystallization opens a new door for the science and technology in crystal growth engineering.

En faceparametric imaging of tissue birefringence using polarization-sensitive optical coherence tomography

A technique for generating en face parametric images of tissue birefringence from scans acquired using a fiber-based polarization-sensitive optical coherence tomography (PS-OCT) system utilizing only a single-incident polarization state is presented. The value of birefringence is calculated for each A-scan in the PS-OCT volume using a quadrature demodulation and phase unwrapping algorithm. The algorithm additionally uses weighted spatial averaging and weighted least squares regression to account for the variation in phase accuracies due to varying OCT signal-to-noise-ratio. The utility of this technique is demonstrated using a model of thermally induced damage in porcine tendon and validated against histology. The resulting en face images of tissue birefringence are more useful than conventional PS-OCT B-scans in assessing the severity of tissue damage and in localizing the spatial extent of damage.

Compact static imaging spectrometer combining spectral zooming capability with a birefringent interferometer

A compact static birefringent imaging spectrometer (BIS) with spectral zooming capability is presented. It based on two identical Wollaston prisms and has no slit. The most significant advantage of the BIS is that we can conveniently select spectral resolution to adapt to different application requirements and greatly reduce the size of the spectral image data for capturing, saving, transferring, and processing. Also, we show this configuration blend the advantage of a grating spectrometer and a Michelson interferometer: extremely compact, robust, wide free spectral range and very high throughput.

Residual stress and dislocations density in silicon ribbons grown via optical zone melting

We investigate the relationships between growth rate, time-temperature profile, residual stress, dislocation density, and electrical performance of silicon ribbons grown via optical zone melting. The time-temperature profiles of ribbons grown at different velocities were investigated using direct measurements and computational fluid dynamics (CFD) modeling. Residual stresses up to 20 MPa were measured using infrared birefringence imaging. The effect of crystallization speed on dislocation density and residual stress is discussed from the context of thermal stresses during growth. More broadly, we demonstrate the usefulness of combining spatially resolved stress and microstructure measurements with CFD simulations toward optimizing kerfless silicon wafer quality.

Wavenumber Dependence of FT-IR Image of Molecular Orientation in Banded Spherulites of Poly(3-hydroxybutyrate) and Poly(l-lactic acid)

The chemical and the molecular chain orientation image of a banded spherulite of crystalline polymers, poly(l-lactic acid) (PLLA) and poly(3-hydroxybutyrate) (PHB), are visualized using FT-IR imaging with a newly proposed multipolarization calculation method. The vector representation of FT-IR image at different absorption spectral peaks visualizes the magnitude and direction of molecular chain orientation directly in comparison with the retardation and the slow-axis azimuthal images obtained by birefringence imaging. We found for the first time that the wavenumber dependence of in-plane orientation function in the band structure of a PHB spherulite, which is known as a double-band structure originated from a biaxial refractive index ellipsoid. The 15 absorption peaks in the IR spectrum of PHB can be classified into three groups by a different appearance of a band structure in view of the magnitude of molecular chain orientation. The azimuthal image of birefringence also shows the double-band structure; however, the FT-IR azimuthal images of orientation axis indicate the completely different distribution in which there is no band structure at any IR absorption peaks. By contrast, a good correspondence between the azimuthal image of the slow axis of birefringence and the orientation axis of FT-IR is observed in the spherulite of PLLA, which has a uniaxial refractive index ellipsoid. The advanced FT-IR imaging method clarifies the wavenumber-dependent two-types single-band structures of PHB, indicating the local molecular chain orientation along the crystallographic axes in a unit cell.

Skin collagen fiber molecular order: a pattern of distributional fiber orientation as assessed by optical anisotropy and image analysis.

BackgroundBirefringence can reveal much of the morphology, molecular order, heterogeneity of fiber orientation, and nonlinear optical properties of biopolymers such as collagen. However, the detailed characterization of skin collagen fibers using optical anisotropy methods remains elusive. A clear understanding of collagen fiber organization in skin tissues may be important in the interpretation of their structural-functional relationships under normal and pathological conditions. In this study, fiber orientation in collagen bundles (CBs) and their supramolecular organization were examined in rat skin using polarization microscopy and image analysis.Methodology/Principal FindingsImage variations with rotation of the microscope stage and selection of the in-depth focus plane were investigated in unstained sections of varying thicknesses from rat skin fragments. Total birefringence (image analysis) and form and intrinsic birefringence (Sénarmont’s method) were estimated. Based on the birefringent images, CBs were found to contain intercrossing points with a twisted helical distribution of collagen fibers (chiral elements) and frequently presented circular structures. Collagen fibers were observed to extend from the surface level to deeper planes, creating a 3D-network of oriented intertwined CBs. At least three levels of birefringent brilliance intensity were revealed by image analysis, indicating a heterogeneous spatial organization of the CBs. Slight differences in optical retardations were found for CBs immersed in some of the fluids used in a comparison of 170- and 240-day old rats.Conclusion/SignificancePolarization microscopy studies provide detailed high-quality structural information on rat skin CBs. A 3D-network structure based on image analysis and birefringence compensation for collagen fibers is suggested for CBs. Form and intrinsic birefringence evaluation can reveal differences in the rat skin associated with age at the levels of collagen fiber crystallinity and macromolecular organization. These findings may inspire future studies of the feedback mechanisms by which spatial, bioelectrical and biomechanical information is transmitted from CBs to skin cells.

Heterogeneity of deformation of aortic wall at the microscopic level: Contribution of heterogeneous distribution of collagen fibers in the wall

There is growing evidence of heterogeneous distribution of collagen fibers in the aortic wall. To investigate the effects of collagen microstructure on local aortic wall deformation, porcine thoracic aortas were sliced into 100 μm-thick sections perpendicular to their radial direction and stretched biaxially with a laboratory-made tensile tester under a microscope equipped with a birefringence imaging system. Strain tensor components were calculated from fluorescent images of the cell nuclei for each 50 × 50 μm² area. Retardance Ret and slow axis azimuth θ were measured as indices of collagen density and fiber direction, respectively. Aortic wall deformation was highly heterogeneous: standard deviations of strains were significantly larger, by 3-5 times, in aortic slices than in homogeneous silicone sheets. A significant negative correlation was found between maximum principal strain and Ret (R=-0.077), and a positive correlation between minimum principal strain direction and θ (R=0.345). These indicate that the aorta is less distensible in areas with higher collagen density and in the direction of collagen fiber alignment. Microscopic heterogeneity may induce heterogeneous responses of smooth muscle cells and have crucial effects on mechanical homeostasis in the aortic wall.

Transient overshoot extensional rheology of long-chain branched polyethylenes: Experimental and numerical comparisons between filament stretching and cross-slot flow

This work analyses the high-strain extensional behavior of long-chain branched polyethylenes, employing two novel extensional rheometer devices, the filament stretching rheometer and the cross-slot extensional rheometer. The filament stretching rheometer uses an active feedback loop to control the imposed strain rate on a filament, allowing Hencky strains of around 7 to be reached. The cross-slot extensional rheometer uses optical birefringence patterns to determine the steady-state extensional viscosity from planar stagnation point flow. The two methods probe different strain-rate regimes and in this paper we demonstrate the agreement when the operating regimes overlap and explore the steady-state extensional viscosity in the full strain-rate regime that these two complimentary techniques offer. For long-chain branched materials, the cross-slot birefringence images show a double cusp pattern around the outflow centre line (named W-cusps). Using constitutive modeling of the observed transient overshoot in extension seen in the filament stretching rheometer and using finite element simulations we show that the overshoot explains the W-cusps seen in the cross-slot extensional rheometer, further confirming the agreement between the two experimental techniques.

Metripol birefringence imaging of unconsolidated glaciotectonized and ice keel scoured sediments: identification of unistrial plasmic fabric

In unconsolidated sediments subject to strain, clays and silts are realigned into particular optical birefringent arrangements (plasmic fabrics), which provide information on the style and intensity of sediment deformation. A relatively new, non‐destructive, optical microscopy technique for automatically recording and quantifying birefringence (previously commercialized under the name ‘Metripol’) is pioneered in this study as a valuable and innovative micromorphological tool with which to examine deformation in unconsolidated sediments. Metripol is applied to unistrial plasmic fabric in glaciotectonized and ice keel scoured sediment from the Netherlands and former Glacial Lake Agassiz (Manitoba, Canada) respectively. Colour‐coded images are produced in which colour represents relative optical retardation and thus optical anisotropy through the quantity |sinδ| and optical orientation of anisotropy through the angle Ø (also indicated by linear azimuths). In this study Metripol typically demonstrates that the better developed the unistrial plasmic fabric is, the higher the |sinδ| values, the larger the areas of high |sinδ| values, and the longer and more densely populated the azimuths. In addition, some unistrial plasmic fabrics under Metripol demonstrate lower |sinδ| than previous examples and the surrounding sediment, despite being ‘perceived’ as demonstrating higher birefringence under a standard petrographic microscope. This is particularly true in clay‐rich sediments and has implications for the way we currently describe and interpret unistrial plasmic fabrics in unconsolidated sediment. Finally, the identification and quantification of additional structures that would otherwise have gone undetected using a standard petrographic microscope (e.g. linear and circular structures that are likely to represent discrete shears and skelsepic plasmic fabric, respectively) highlight the potential for Metripol to gather information on the deformation history of unconsolidated sediments that is unavailable to standard techniques.

Imaging of Two-Dimensional Distribution of Molecular Orientation in Poly(ethylene oxide) Spherulite Using IR Spectrum and Birefringence

The two-dimensional quantitative imaging of molecular chain orientation is presented together with a chemical FT-IR imaging, in comparison with the optical birefringence imaging. The molecular chain orientation of the spherulite of poly(ethylene oxide) (PEO) is visualized using the four polarizations method of FT-IR imaging. The magnitude of orientation function and the azimuth angle of orientation axis are calculated with the FT-IR absorbance measured with a linear polarizer settled at four different angles. Retardation and the slow axis in a refractive index ellipsoid are calculated using transmission intensity measured with an electrical-controlled variable elliptical analyzer and a circular polarizer. In spite of the 6 times difference of the spatial resolution, the azimuth angle image determined from FT-IR imaging detects the change of molecular chain orientation, giving the similar line profiles of azimuth angle to that of slow axis determined from birefringence on the spherulite interface. A good c...

Optical Rheology of Porcine Sclera by Birefringence Imaging

PurposeTo investigate a relationship between birefringence and elasticity of porcine sclera ex vivo using polarization-sensitive optical coherence tomography (PS-OCT).MethodsElastic parameters and birefringence of 19 porcine eyes were measured. Four pieces of scleral strips which were parallel to the limbus, with a width of 4 mm, were dissected from the optic nerve head to the temporal side of each porcine eye. Birefringence of the sclera was measured with a prototype PS-OCT. The strain and force were measured with a uniaxial material tester as the sample was stretched with a speed of 1.8 mm/min after preconditioning. A derivative of the exponentially-fitted stress-strain curve at 0% strain was extracted as the tangent modulus. Power of exponential stress-strain function was also extracted from the fitting. To consider a net stiffness of sclera, structural stiffness was calculated as a product of tangent modulus and thickness. Correlations between birefringence and these elastic parameters were examined.ResultsStatistically significant correlations between birefringence and all of the elastic parameters were found at 2 central positions. Structural stiffness and power of exponential stress-strain function were correlated with birefringence at the position near the optic nerve head. No correlation was found at the position near the equator.ConclusionsThe evidence of correlations between birefringence and elasticity of sclera tested uniaxially was shown for the first time. This work may become a basis for in vivo measurement of scleral biomechanics using PS-OCT.

Precursor dynamics in rhodium-doped barium titanate single crystals studied by Brillouin light scattering and birefringence measurements

The dynamics of precursor polar clusters in rhodium(Rh)-doped barium titanate single crystals were examined in the paraelectric phase by Brillouin light scattering and birefringence measurements in a wide temperature range. The longitudinal acoustic (LA) mode and central peaks in the inelastic light scattering spectrum were investigated by Brillouin scattering, while the temperature dependence of the birefringence was accurately determined by means of a birefringence imaging system. In a specific temperature range above the ferroelectric phase transition temperature, the LA mode frequency exhibited a significant softening concomitant with the substantial increase in the hypersonic damping, which was attributed to the formation of polar clusters and their interactions with acoustic waves. In this temperature range where acoustic anomalies were brought about, the birefringence showed non-zero values, indicating the existence of local non-centrosymmetric regions. All these results clearly indicated that the off-centered motions of Ti ions in the oxygen octahedra in Rh-doped BaTiO3 are correlated in the paraelectric phase inducing slowing down of the precursor dynamics and anomalous birefringence, similar to pure BaTiO3 (Ko et al., Phys. Rev. B 84, 094123 (2011)). The effect of rhodium doping in BaTiO3 enhanced the first-order character of the ferroelectric phase transition.