Birefringence Changes Research Articles

Acoustic Birefringence Changes in the Base Metal and Heat Affected Zone of ASTM 1020 Steel under Plastic Deformation and Fatigue

This paper deals with metallographic studies and ultrasonic investigations of acoustic birefringence in the base metal and heat affected zone of welded specimens of ASTM 1020 steel under uniaxial tension and low-cycle fatigue. We examined microstructural changes on the surface using optical microscope. It was found that development of slip bands differs in the base metal and heat affected zone. The ultrasonic pulse echo method was used for the determination of acoustic birefringence and velocities of ultrasonic shear waves. The differences in the change in velocities in the base metal and in heat affected zone were revealed. Acoustic birefringence was found to change monotonously in the base metal under fatigue as well as in the base metal and heat affected zone under uniaxial tension. For heat affected zone, during fatigue, acoustic birefringence was found to change non-monotonously up to cycle ratio of 0.3 and decrease monotonously after cycle ratio of 0.3. Based on the relationship between relative number of loading cycles, or plasticity resource, and acoustic birefringence, ultrasonic techniques were proposed for assessing damage.

Phase transformation in some hexahydrated metal(II) fluorogermanates and fluorotitanates: Optical and differential scanning calorimetry studies

• Single crystals of hydrated fluorides CoGeF 6 ∙6H 2 O, FeGeF 6 ∙6H 2 O, CoTiF 6 ∙6H 2 O, ZnTiF 6 ∙6H 2 O were grown. • Twinning, birefringence and heat capacities indicate a phase transition of the first order from trigonal to monoclinic symmetry. • Small values of the change in entropy and birefringence accompany the phase transition of CoGeF 6 ∙6H 2 O and FeGeF 6 ∙6H 2 O, and rather large values are typical for CoTiF 6 ∙6H 2 O and ZnTiF 6 ∙6H 2 O. Graphical abstract_Synopsis!!! Polarization-optical observations of (001) section of an ABF 6 ∙6H 2 0 crystals: a − optically isotropic rhombohedra phase ( T > T 0 ). Twin pattern in the studied crystals at Т < Т 0 : b − CoGeF 6 ∙6H 2 O; c − FeGeF 6 ∙6H 2 O; d − FeTiF 6 ∙6H 2 O; e − CoTiF 6 ∙6H 2 O; f − ZnTiF 6 ∙6H 2 O.

Birefringence induced by antiferroelectric switching in transparent polycrystalline PbZr0.95Ti0.05O3 film

The most characteristic functional property of antiferroelectric materials is the possibility to induce a phase transition from a non-polar to a polar phase by an electric field. Here, we investigate the effect of this field-induced phase transition on the birefringence change of $PbZr_{0.95}Ti_{0.05}O_{3}$. We use a transparent polycrystalline $PbZr_{0.95}Ti_{0.05}O_{3}$ film grown on $PbTiO_{3}/HfO_{2}/SiO_{2}$ with interdigitated electrodes to directly investigate changes in birefringence in a simple transmission geometry. In spite of the polycrystalline nature of the film and its moderate thickness, the field-induced transition produces a sizeable effect observable under a polarized microscope. The film in its polar phase is found to behave like a homogeneous birefringent medium. The time evolution of this field-induced birefringence provides information about irreversibilities in the antiferroelectric switching process and its slow dynamics. The change in birefringence has two main contributions, one that responds briskly (~ 0.5 s), and a slower one that rises and saturates over a period of as long as 30 minutes. Possible origins for this long saturation and relaxation times are discussed.

Distributed birefringence sensing at 10-9 accuracy over ultra-long PMF by optical frequency comb and distributed Brillouin amplifier.

Brillouin dynamic gratings (BDG) can measure the distributed birefringence of polarization-maintaining fibers (PMF), however, its sensing range is limited by both stimulated Brillouin scattering depletion and fiber losses in PMF, which are significantly higher than those in standard single-mode fibers. In this work, we theoretically and experimentally verify that BDG can be sustained over ultra-long distances when assisted by distributed Brillouin amplification, significantly extending the distributed birefringence measurement distance. Using an optical frequency comb pumped by a narrow linewidth laser to both generate and interrogate the amplified BDG, a birefringence measurement accuracy of 7.5 × 10-9 was achieved over 7 km sensing length, more than double the longest range reported. This opens a new opportunity to investigate small birefringence changes due to nonlinear optics effects and monitoring fiber network security from eavesdropping.

Electrical modification of order parameters and director fluctuations in a dielectrically negative nematic doped with a positive additive

Electric effects of nematic liquid crystals (NLCs) have enabled the revolution of the display industry. Recently, the electro-optic switching of NLCs has been accelerated by applying electric fields in such a way that the field does not change the director orientation, but modifies the optical tensors of NLCs due to three effects: induced biaxial orientational order, enhanced uniaxial orientational order, and quenching of director fluctuations. Till now, these three effects have been explored only in NLCs with negative dielectric anisotropy. Here, we experimentally study the electrical modification of order parameters and director fluctuations in a dielectrically negative/positive composite NLC. The dielectrically positive dopant causes the following changes: (a) a faster nanosecond switching for optical responses attributed to the change of order parameters, (b) an increase of the biaxial order parameter, (c) a reduction of the uniaxial order parameter, and (d) a slight reduction in the field-induced birefringence change. This work provides a basis for further studies in nanosecond electro-optics.

Optical birefringence changes in myelinated and unmyelinated nerves: A comparative study.

The measurement of birefringence variations related to nerve activity is a promising label-free technique for sensing compound neural action potentials (CNAPs). While widely applied in crustaceans, little is known about its efficiency on mammal peripheral nerves. In this work, birefringence recordings to detect CNAPs, and Stokes parameters measurements were performed in rat and lobster nerves. While single-trial detection of nerve activity in crustaceans was achieved successfully, no optical signal was detected in rats, even after extensive signal filtering and averaging. The Stokes parameters showed that a high degree of polarization of light is maintained in lobster sample, whereas an almost complete light depolarization occurs in rat nerve. Our results indicate that depolarization itself is not sufficient to explain the absence of birefringence signals in rats. We hypothesize that this absence comes from the myelin sheets, which constraint the birefringence changes to only take place at the nodes of Ranvier.

Distributed temperature–strain sensor based on inter-mode Kerr four-wave mixing of PMF: proposal and proof-of-concept

A novel concept of distributed temperature–strain sensors is proposed using inter-mode Kerr four-wave mixing of polarization-maintaining fiber (PMF), in which the dominated physical mechanism is basically different from reported Brillouin dynamic grating (BDG). The independent measurement for temperature and strain sensitivities (−0.431 MHz °C−1 and 0.067 MHz/10 με) was completed by detecting the change in birefringence under pump-Stokes frequency separation at 370 MHz. As a preliminary proof-of-concept, sensing with a spatial resolution of ∼5 m was demonstrated along ∼210 m PMF. Compared with BDG, the proposed sensor features potential of multiple parameters measurement including temperature–strain and liquid acoustic impedance.

A Magnetic Field Sensor Based on Birefringence Effect in Asymmetric Four-Hole Fiber

A Sagnacinterferometer-based magnetic field sensor is theoretically proposed and experimentally demonstrated by taking advantage of the high birefringence of an asymmetric four-hole fiber (AFHF) as well as the sensibility of magnetic fluid (MF) to magnetic field. A variation in the magnetic field intensity would induce a change in the RI of MF, leading to a birefringence change of MF-filled AFHF and resulting in a shift of the interference spectrum. The magnetic field sensing can be realized by monitoring the spectral shift. The proposed sensor has a high sensitivity of 226.2 pm/Gs (2.96 ∼ 89 Gs) with a measurement accuracy of 0.221 Gs, accompanied with competitive linearity, good repeatability and stability. In addition, it is insensitive to ambient temperature disturbance. The proposed sensor can be used in industry, biomedicine, aerospace and other fields which require a magnetic field measurement with high precision and good stability.

Effect of Temperature on the Surface Plasmon Resonance (SPR) Mode along a Metal - Liquid Crystal Interface

The effect of temperature on the surface plasmon mode parameters for surface plasmons (SPs) excited by prism coupling along the interface of a thin silver film and homeotropically aligned liquid crystals (LCs), 5CB and UCF25 are theoretically studied. The change in the SPR angle of dip with temperature is found to be almost linear below the clearing temperature of the LCs. The temperature sensitivity is found to be high in the temperature range where the LC behaves as an anisotropic material. The sensitivity is found to be higher when SPR reflectance at a fixed incident angle is used as the variable parameter. The shift in SPR angle of dip is found to be linear with the change in birefringence of the LC due to the change in temperature. The change in SPR parameters with temperature is found to be much lesser in the temperature range where the LC behaves as an isotropic material.

Research on the Birefringence Distribution of the Fiber Coil With Quadrupole Symmetrical Winding Method

As the core component of the fiber optic gyroscope, the fiber coil has been the focus of research. In the field of fiber coil environmental adaptability research, researchers are calculating environmental errors, such as thermally-induced errors and magnetic-induced errors. They approximated the refractive index and birefringence of the fiber coil to an average value. However, the values of birefringence changes by the different bending radius of the fibers in the different layers, which would greatly reduce the accuracy of the environment error model. Therefore, in this paper, a birefringence distribution model of the fiber coil is proposed for the first time based on the quadrupole symmetrical winding pattern. Firstly, we qualitatively analyze the birefringence of Panda-type polarization-maintaining fiber, and then the fiber coil winding law is established through detailed analysis of the standard quadrupole symmetric winding method. Secondly, we use the finite element method to analyze the force of the single-layer fiber, and obtain the change law of the refractive index of polarization-maintaining fiber. The mathematical model of the birefringence distribution is established and simulated. Finally, we use optical coherence domain polarization measurement technology to detect the distributed polarization crosstalk of the fiber coil. The data is obtained by using the white light interferometer that is consistent with the simulation. The result proves the correctness of the theory. Moreover, an experimental platform for Sagnac loop is built, and the interference optical power is measured by the optical spectrum analyzer. Compared with the equivalent radius method, the accuracy of model is improved by 91.48% at 1310nm.The method proposed in this paper will greatly promote the research on the environmental adaptability of fiber optic gyroscope.

Multicontrast investigation of in vivo wildtype zebrafish in three development stages using polarization-sensitive optical coherence tomography.

.Significance: The scattering and polarization characteristics of various organs of in vivo wildtype zebrafish in three development stages were investigated using a non-destructive and label-free approach. The presented results showed a promising first step for the usability of Jones-matrix optical coherence tomography (JM-OCT) in zebrafish-based research.Aim: We aim to visualize and quantify the scatter and polarization signatures of various zebrafish organs for larvae, juvenile, and young adult animals in vivo in a non-invasive and label-free way.Approach: A custom-built polarization-sensitive JM-OCT setup in combination with a motorized translation stage was utilized to investigate live zebrafish. Depth-resolved scattering (intensity and attenuation coefficient) and polarization (birefringence and degree of polarization uniformity) properties were analyzed. OCT angiography (OCT-A) was utilized to investigate the vasculature label-free and non-destructively.Results: The scatter and polarization signatures of the zebrafish organs such as the eye, gills, and muscles were investigated. The attenuation coefficient and birefringence changes between 1- and 2-month-old animals were evaluated in selected organs. OCT-A revealed the vasculature of in vivo larvae and juvenile zebrafish in a label-free manner.Conclusions: JM-OCT offers a rapid, label-free, non-invasive, tissue specific, and three-dimensional imaging tool to investigate in vivo processes in zebrafish in various development stages.

Assessment of Changes in Birefringence and Orientation of Collagen Fibres in Different Grades of Oral Submucous Fibrosis and Oral Squamous Cell Carcinoma using Picrosirius Red and Polarising Microscopy

Introduction: Oral submucous fibrosis (OSMF) is a potentially malignant disease with a prevalence of 7-13%. It is characterised by the fibroelastic changes due to excessive deposition of collagen which results in dense fibrous bands and epithelial changes. About 90-95% of oral cancers are Oral Squamous Cell Carcinoma (OSCC). Stroma produced by the invading neoplastic cells are rich in collagen fibres. These collagen fibers have been the main focus of study to understand the pathogenesis of these lesions. Hence, these fibres have been evaluated under polarised microscopy following staining with Picrosirius red stain. Aim: To evaluate changes in birefringence, thickness and orientation of collagen fibres in different histopathological stages of OSMF and OSCC. Materials and Methods: This observational study involved sections of clinically and histopathologically confirmed cases of OSCC and OSMF from Department of Oral Pathology and Microbiology, Rajarajeswari Dental College and Hospital, Bangalore. The study was conducted for a duration of one year from April 2017 to March 2018. The study included total 60 cases among which 20 for each-normal mucosa, OSCC and OSMF. Tissue sections were stained with Picrosirius red stain and collagen fibres were analysed for colour, thickness and orientation under polarised microscope. Chi-square test was used for statistical analysis. Significance was set at p-value &lt;0.05. Results: Comparison of birefringence of collagen fibres between OSMF, OSCC and normal mucosa was not statistically significant (p-value=0.37). Orientation of collagen fibres between OSMF, OSCC and normal mucosa was statistically significant with (p-value=0.02). Conclusion: This study showed a change in colour from yellow orange to orange red in advanced OSMF cases which indicated progression of disease and tightly packing of collagen fibres, suggestive of presence of thick fibres in the extracellular matrix. In OSCC, the colour change from yellow orange to orange red and haphazardly arranged collagen fibres was indicative of transformation of preneoplastic to carcinoma stage.

CRYSTAL OPTICAL PARAMETERS OF UNIAXIALLY COMPRESSED LiNaSO4 CRYSTALS

In the work, a LiNaSO 4 crystal was synthesized and spectral study of its birefringence Δ n i was carried out. It was found that the cation substitution of potassium with sodium(LiKSO 4 → LiNaSO 4 ) in the LiBSO 4 systemsignificantly increases the refractive index and birefringence (by more than an order of magnitude) compared to the substitutions K + → Rb + and K + → (NH 4 ) + . It is shown that the high optical anisotropy of the lithium sodium sulfate crystal can be related to the asymmetry of the second coordination environment of anions in its structure. First-principles calculations of the electronic and optical properties of LiNaSO 4 crystals were performed. From the calculated spectra of the real and imaginary parts of the dielectric function, the spectral dependence of the refractive indices and the extinction coefficients were obtained. The calculated dispersions of the refractive indices of the LiNaSO 4 crystalfor the visible part of the spectrum satisfy the ratio n z &gt; n x,y . The order of the obtained curves coincides with those determined experimentally. The theoretically obtained values of refractive indices are lower (within 8%) than the experimental ones. Such a deviation can be caused by the negative contribution of infrared absorption in the crystal, which is not taken into account in the CASTEP code. It is worth noting, however, that a very good reproduction of the dispersion changes of the refractive indices was obtained from the calculations. Here, the values of d (Δ n i )/ dλ for n x,y (λ) and n z (λ) dependences are practically the same with the maximum deviation of 3.3·10 –5 nm –1 from those determined experimentally. The behavior of optical birefringence of LiNaSO 4 crystals was studied under conditions of uniaxial pressures applied along the main crystal physical directions. The uniaxial pressure applied along mutually perpendicular directions was found to lead to changes in birefringence, different in magnitude and sign. Dispersion effect of birefringence weakens under the influence of stress σ ⊥ z and strengthens in the opposite case of σ || z. Keywords : crystal, birefringence, uniaxial pressure, piezo-optical coefficients, refractive index.

Change in Texture-Dependent Acoustic Birefringence in α-Fe and γ-Fe Polycrystalline Aggregates due to Plastic Deformation

Change in Texture-Dependent Acoustic Birefringence in α-Fe and γ-Fe Polycrystalline Aggregates due to Plastic Deformation

Group Birefringence Regulation and Measurement With Twin Zeros in a Selectively Infiltrated Microstructured Optical Fiber Based on OFDR

We propose and demonstrate a selectively microfluidic-infiltrated method for the group birefringence regulation in a microstructured optical fiber. Meanwhile, an Optical Frequency Domain Reflectometry (OFDR) with an equivalent resolution of 0.6 Hz or 10-6 RIU is utilized to characterize its polarization separation and group birefringence change. By selectively infiltrating a fluid with a high thermal-optic coefficient into twin air holes nearby the silica fiber core, tunable group birefringence is observed and measured by polarization separation in beat frequency domain. Moreover, due to the co-effects of the filled and unfilled fiber segments, the twin critical zeros of the overall group birefringence are observed at 16.5 and 43.0, respectively. The unique position exchange of LP01x and LP01y presents at the twin critical zeros, which is investigated via the OFDR technique as well. Therefore, by combining the unfilled fiber segment with negative group birefringence and filled fiber segment with positive group birefringence, dual zeros in group birefringence are achieved with position exchange of the LP01x and LP01y peaks in beat frequency domain. Our demonstration provides potentials in flexible regulation and real-time observation of the group birefringence in microstructured optical fiber.

Polymerization enabled reduction of the electrically induced birefringence change in nematic liquid crystals

Polymerization enabled reduction of the electrically induced birefringence change in nematic liquid crystals

Fatigue life prediction of structural steel using acoustic birefringence and characteristics of persistent slip bands

AbstractNondestructive evaluation methods provide additional information about the material fatigue behavior and enhance the comprehension of damage evolution thanks to relationship between microstructure and physical properties. This paper deals with optical and ultrasonic investigations of structural steel specimens tested for low‐cycle fatigue. The development of persistent slip bands observed on the surface with an optical microscope was quantified using a previously trained neural network and fractal analysis. A surface damage parameter was defined as the ratio of total area of detected slip bands to the area of observed surface. Relationships between the rate of change and critical value of the damage parameter, the strain range, and the fatigue life were established. A single square relationship between relative number of cycles and ratio of the surface damage parameter to its critical value was obtained. Acoustic birefringence was measured by the echo method. The effect of the strain range on the rate of change in acoustic birefringence was investigated. A single linear relationship between relative number of cycles and change in acoustic birefringence was established. An algorithm for predicting the material remaining life, combining optical and ultrasonic data, was proposed.

Temperature effects on liquid crystal-based tunable biosensors

A novel tunable surface plasmon resonance biosensor based on liquid crystal is demonstrated. The liquid crystal surface plasmon resonance (LC-SPR) biosensor response to temperature was studied for four usual 5CB, 5PCH, E7, and E44 nematic liquid crystals by modeling and simulation. The results indicated that after including the analyte, the change of liquid crystal birefringence occurs differently at various temperatures. Consequently, the variation of biological agents can be detected by the shift of the surface plasmon resonance angle. The results show that the temperature variation of maximum sensitivity occurs for the homogeneous alignment more than the homeotropic alignment. But the maximum sensitivity increasing rate in homeotropic alignment, is approximately two times greater than homogeneous alignment, in the near of transition temperatures. In the nematic to isotropic transition region, the maximum sensitivity increasing rate is 3.05 Deg/RIU°C for 5CB and 1.03 Deg/RIU°C for 5PCH based biosensors for homeotropic alignment. The sensitivity of 5CB and 5PCH based biosensors is greater than E7 and E44 liquid crystals.

Temperature-insensitive directional transverse load sensor based on dual side-hole fiber Bragg grating.

We propose and demonstrate a temperature-insensitive directional transverse load sensor based on a fiber Bragg grating (FBG) inscribed in a section of dual side-hole fiber (DSHF). The application of transverse load results in an effective change in the refractive index and, consequently, changes in the DSHF birefringence. The directional transverse load response of the fabricated DSH-FBG was studied by monitoring the wavelength separations with transverse load applied in different direction with 15° increments. The load sensitivity exhibited two maxima and two minima in a polar coordinate system, achieving a maximum value of 699 pm/(N/mm) for transverse load applied along the slow axis and a minimum value of 285 pm/(N/mm) for transverse load applied along the fast axis. Subsequently, a finite element analysis (FEA) was conducted to simulate the resulting strain distribution of the DSHF with applied directional transverse load. The temperature response of the DSH-FBG transverse load sensor was also tested, yielding a low sensitivity of 1.5 × 10-2 pm/°C. Hence, the compact size, directional transverse load sensitivity, and temperature insensitivity of this device make it suitable for intelligent transverse load monitoring.

Dependence of phase transition uniformity on crystal sizes characterized using birefringence.

Solid–solid phase transitions (SSPTs) have been widely observed in crystals of organic or inorganic small-molecules. Although SSPTs in macromolecular crystals have been reported, the majority involve local atomic changes, such as those induced by changes in hydration. SSPTs driven by large conformational changes, however, can be more difficult to characterize since they often significantly disrupt lattice packing interactions. Such drastic changes make the cooperativity of molecular motion at the atomic level less easily achieved and more dependent on intrinsic properties of the crystal that define lattice order. Here, we investigate the effect of crystal size on the uniformity of SSPT in thin plate-like crystals of the adenine riboswitch aptamer RNA (riboA) by monitoring changes in crystal birefringence upon the diffusion of adenine ligand. The birefringence intensity is directly related to molecular order and the concurrent changes to polarizability of molecules that results from structural changes throughout the phase transition. The riboA crystals were loosely grouped into three categories (small, medium, and large) based on the surface area of the crystal plates. The time width of transition increased as a function of crystal size, ranging from ∼13 s for small crystals to ∼40 s for the largest crystal. Whereas the transitions in small crystals (<10 μm2) were mostly uniform throughout, the medium and large crystals exhibited large variations in the time and width of the transition peak depending on the region of the crystal being analyzed. Our study provides insight into the spatiotemporal behavior of phase transitions in crystals of biological molecules and is of general interest to time-resolved crystallographic studies, where the kinetics of conformational changes may be governed by the kinetics of an associated SSPT.