Anomalous Birefringence Research Articles

Effect of isothermal annealing on the optical properties of Ca<sub>3</sub>TaGa<sub>3</sub>Si<sub>2</sub>O<sub>14</sub> crystals

The effect of post-growth isothermal annealing in vacuum and in air on the optical properties of Ca3TaGa3Si2O14 crystal samples of Z and X-cuts has been studied. Spectral dependences of transmission coefficients were measured in the wavelength range (240–700) nm taking into account anisotropy and dichroism. On the Z-cut samples in the initial state an absorption band at λ = 360 nm in the ultraviolet range is observed, in the visible region – two absorption bands at λ = 460 nm and λ = 605 nm. Additionally, a band at λ = 290 nm was observed on the X-cut samples. When the sample was rotated around the direction of the light beam by 90 degrees, a change in the intensity of the absorption bands was observed. Annealing in vacuum leads to a decrease in the intensity of the absorption bands in the near ultraviolet and visible range, except for the absorption band at λ = 605 nm. Annealing in air leads to the opposite effect – an increase in the intensity of the absorption bands, except for the band λ = 605 nm. The value of the anomalous birefringence of the samples was estimated by the Mallard method. The degree of linear dichroism is calculated. It is shown that the degree of dichroism decreases as a result of annealing in vacuum, and increases during annealing in air.

Polarization-sensitive optical responses from natural layered hydrated sodium sulfosalt gerstleyite

Multi-element layered materials have gained substantial attention in the context of achieving the customized light-matter interactions at subwavelength scale via stoichiometric engineering, which is crucial for the realization of miniaturized polarization-sensitive optoelectronic and nanophotonic devices. Herein, naturally occurring hydrated sodium sulfosalt gerstleyite is introduced as one new multi-element van der Waals (vdW) layered material. The mechanically exfoliated thin gerstleyite flakes are demonstrated to exhibit polarization-sensitive anisotropic linear and nonlinear optical responses including angle-resolved Raman scattering, anomalous wavelength-dependent linear dichroism transition, birefringence effect, and polarization-dependent third-harmonic generation (THG). Furthermore, the third-order nonlinear susceptibility of gerstleyite crystal is estimated by the probed flake thickness-dependent THG response. We envisage that our findings in the context of polarization-sensitive light-matter interactions in the exfoliated hydrated sulfosalt layers will be a valuable addition to the vdW layered material family and will have many implications in compact waveplates, on-chip photodetectors, optical sensors and switches, integrated photonic circuits, and nonlinear signal processing applications.

Anomalous birefringence and nonlinearity enhancement of As2S3 and As2S5 filled D-shape fiber for optical communication

An elliptical core-based D-shape photonic crystal fiber (PCF) has been proposed with achieving extraordinary optical properties in this paper. We deeply observed and evaluated the performance of the designed D-PCF by doping the materials (As2S3 and As2S5) separately into the core region with the variation of the eccentricities (core size). After the whole analysis, this D-PCF prefers the As2S3 core material because it produces a better performance of all the optical features compared to the As2S5 material. The results of the raised PCF shows that the maximum nonlinearity of 9.114 × 104 W−1 km−1, the extreme-high birefringence of 0.254, the better power fraction of 99.51%, the high numerical aperture of 0.78, the large negative dispersion of −2560.12 ps/(nm-km), and the low beat length of 7.09 μm, etc. The finite element method (FEM) has been applied to simulate the optical characteristics and a perfectly matched layer (PML) is used as a boundary condition. So, the above mentioned remarkable outcomes of the designed D-PCF makes it a robust candidate in many helpful applications like biomedical imaging, telecom, super-continuum generation, and polarization-maintaining signal processing.

Visualization of the Effect of an Impurity on the Optical Homogeneity of Lithium Niobate Doped with Boron Cations

The laser conoscopy method confirms the high optical uniformity of LiNbO3:B crystals in the range of B2O3 concentrations from 0.008 to 1.24 mol. %. Minor signs of anomalous optical biaxiality appear in the conoscopic patterns of crystals at boron concentrations of 0.12 and 0.83 mol. % at a laser power of 90 mW. The maximum value of the angle of anomalous optical axes for the studied samples is 2V = 10 ́ for the sample (0.12 mol. %), аnd the value of anomalous birefringence corresponds to ∆n = 0.02·10-5.

Nitrogen-doped CVD diamond: Nitrogen concentration, color and internal stress

Single crystal CVD diamond has been grown on (100)-oriented CVD diamond seed in six layers to a total thickness of 4.3 mm, each layer being grown in gas with increasing concentration of nitrogen. The nitrogen doping efficiency, distribution of color and internal stress have been studied by SIMS, optical absorption, Raman spectroscopy and birefringence imaging. It is shown that nitrogen doping is very non-uniform. This non-uniformity is explained by the terraced growth of CVD diamond. The color of the nitrogen-doped diamond is grayish-brown with color intensity gradually increasing with nitrogen concentration. The absorption spectra are analyzed in terms of two continua representing brown and gray color components. The brown absorption continuum exponentially rises towards short wavelength. Its intensity correlates with the concentration of nitrogen C-defects. Small vacancy clusters are discussed as the defects responsible for the brown absorption continuum. The gray absorption continuum has weak and almost linear spectral dependence through the near infrared and visible spectral range. It is ascribed to carbon nanoclusters which may form in plasma and get trapped into growing diamond. It is suggested that Mie light scattering on the carbon nanoclusters substantially contributes to the gray absorption continuum and determines its weak spectral dependence. A Raman line at a wavenumber of 1550 cm−1 is described as a characteristic feature of the carbon nanoclusters. The striation pattern of brown/gray color follows the pattern of anomalous birefringence suggesting that the vacancy clusters and carbon inclusions are the main cause of internal stress in CVD diamond. A conclusion is made that high perfection of seed surface at microscale is not a required condition for growth of low-stress, low-inclusion single crystal CVD diamond. Crystallographic order at macroscale is more important requirement for the seed surface.

Using polarized Raman spectroscopy to study the stress gradient in mineral systems with anomalous birefringence

Polarized Raman spectroscopy was applied to garnet hosts which exhibit anomalous birefringence around inclusions of zircon and quartz to elucidate the spatial distribution of the anisotropic strain fields in the vicinity of the host-inclusion boundary. We show that there is a direct relationship between the stress-induced birefringence and the Raman scattering generated by the fully symmetric phonon modes (the A1g modes in cubic crystals). Our experimental results coupled with selected finite element models show that the ratio between the measured Raman peak intensity collected in cross and parallel polarized scattering geometries of totally symmetric modes represents a useful tool to constrain the radial stress profile in the host around the inclusions. Further, we demonstrate how group-theoretical considerations and tensor analysis of the morphic effect (external-field-induced change of the symmetry) on the phonons and the optical properties of the host can help to derive useful information on the symmetry of the stress field. Finally, we show experimentally that, under the same amount of applied stress, this approach is more sensitive than the commonly used approach of measuring differences in phonon frequencies and provides better opportunities to map the spatial variations of strain. This approach is an alternative technique to study structural phenomena associated with anomalous birefringence in host crystals surrounding stressed inclusions and could be applied to other systems in which similar optical effects are observed.

Anomalous birefringence through metasurface-based cavities with linear-to-circular polarization conversion

We propose the metasurface-based cavities for splitting a linearly polarized (LP) electromagnetic wave into two symmetric circularly polarized (CP) beams with opposite helicities. More specifically, periodic strip slits and rectangular C-slits etched on substrate integrated waveguide cavities are shown to be capable of perfectly coupling the LP wave into the cavities from the strip slit array, and then releasing them with specific polarization directions according to the orientations of the C-slits. Such metasurface-based cavities with gradient oriented C-slit array would further create the opposite equivalent phase gradients for the right-hand and left-hand CP transmitting waves that are decomposed from the released LP wave with anomalous birefractions and polarization conversion simultaneously.

Anomalous birefringence and enhanced magneto-optical effects in epsilon-near-zero metamaterials based on nanorods' arrays.

Hyperbolic metamaterials based on the ordered arrays of metal nanorods in a dielectric media are of great interest owing to new optical effects appearing in such artificial media. Here we study the effects in the polarization state of light passing through a nanocomposite material consisting of Au nanorods in porous alumina and a similar structure supplemented by a nanolayer of ferromagnetic nickel. We demonstrate that close to the epsilon-near-zero dispersion point, under the transition to the hyperbolic dispersion region, the nanocomposites reveal anomalously high modulation of the polarization state of light, which appears as polarization plane rotation and ellipticity changes of probing radiation with a zero ellipticity. This effect is applied for the giant enhancement of the Faraday effect in a continuous ferromagnetic film staying in contact with hyperbolic material. These findings open a path for the design of polarization state control by using hyperbolic metamaterials.

Ca3(VO4)2:Tm3+—A new crystalline medium for 2-μm lasers

Calcium orthovanadate crystals doped with Tm3+ ions were successfully grown by Czochralski method. The value of anomalous birefringence did not exceed of 1.3 × 10−5 cm−1 for as-grown samples. The effective segregation coefficient of Tm3+ in a vacancy-compensated crystal was determined as 0.8. It was shown that the formation of the domain structure depends on the crystal composition, crystallization conditions, and annealing treatment. Polarized absorption spectra for heavily doped Ca3(VO4)2:Tm3+ crystal demonstrate a stronger absorption for the E⊥c case. The normalized fluorescence spectra for E⊥c and E||c cases showed about 1.5 times higher maximum fluorescence intensity for E⊥c. Lasing of the thulium doped Ca3(VO4)2 crystal was demonstrated for the first time. The oscillation spectrum was measured to be centered at about 1970 nm with about 20-nm width at half maximum.

Natural End Member Samples of Pyrope and Grossular: A Cathodoluminescence-Microscopy and -Spectra Case Study

Garnet is one of the most significant minerals in metamorphic rocks, that provides key information on prograde, peak-metamorphic and retrograde parts of the pressure-temperature (PT) path. Such results require a detailed knowledge of its different growth domains. For iron-poor compositions, the cathodoluminescence (CL) microscopy is an important and often overlooked method and allows to identify the internal structures of all garnet grains in one thin section within only a few seconds. The advantage of the CL-microscope is to deliver low magnification images in true color, not only of garnet but also, for instance, of other rock forming silicates, carbonates, sulfates, etc., of metamorphic, but also of sedimentary and magmatic origin, using polished thin sections. Internal structures of grossular from Mexico and pyrope from the Italian Alps were characterized and visualized by CL-microscopy. The different growth domains were additionally studied using CL-spectra and electron microprobe (EMP) analysis. Grossular shows a patchy zonation in its core while in mantle and rim zones oscillatory zoning is observed. It contains zones of anomalous birefringence, zones of orange and bluish luminescence and zones lacking luminescence. Different but low amounts of the activator elements Mn2+ and Eu2+ are responsible for the orange and bluish luminescent domains. Pyrope is also characterized by oscillatory growth zones, shows a dull luminescent core with a change of crystal morphology during growth, and displays an increase of brightness from core towards rim—the outermost rim, however, is lacking luminescence. The different luminescent zones are characterized by different amounts of Dy3+, Tb3+, Sm3+ and Sm2+ as activator elements. Because of slow diffusion rates of activators such as the REEs Sm, Dy and Tb, it can be still possible to visualize possible prograde and/or peak pressure stage growth domains of garnet, even if later high temperature events may have homogenized the major element profiles. Such domains may help to identify respective assemblages of mineral inclusions, and hence these results can represent an integral part of a detailed PT path. Thus the CL-information can be used as an important pathfinder prior to supplementary investigations, as for instance EMP, ion probe, mineral or fluid inclusion studies.

Optical Properties and Microdefects in CaMoO4 Single Crystals

Optical inhomogeneities of calcium molybdate crystals in the initial state and after isothermal annealings have been investigated. The value of anomalous birefringence of the samples has been estimated by Mallard’s method; it is shown that annealing reduces this value. Scattering centers have been observed by the Tyndall method. Microscopy has revealed inclusions 2–10 μm in size in all samples. They can’t be attributed to the crucible material inclusions. Light-scattering indicatrices are plotted based on scattering spectroscopy data. Sizes of the scattering centers are estimated.

Electric Birefringence of Aqueous Solutions of a Rigid Polyelectrolyte. Polarization Mechanisms and Anomalous Birefringence Signals

We present an electric birefringence study of aqueous solutions of an intrinsically rigid polyelectrolyte, xanthan, and of mixed solutions with an oppositely charged surfactant, DTAB. The stationary electric birefringence as well as built-up and decay processes give information on the polarization mechanisms of the polyelectrolyte and on the role played by counterions. By adding a cationic surfactant (DTAB), that replaces the small Na+ counterions of the polymer, we could obtain further insights into the role of condensed counterions in these mechanisms. In some cases, anomalous birefringence signals appear, revealing a new polarization mechanism likely due to field-induced interactions within polymer–surfactant aggregates.

X-ray topographic study of a diamond from Udachnaya: Implications for the genetic nature of inclusions

In recent years, several studies have focused on the growth conditions of the diamonds through the analysis of the mineral inclusions trapped in them. In these studies, it is crucial to distinguish between protogenetic, syngenetic and epigenetic inclusions. X-ray topography (XRDT) can be a helpful tool to verify, in a non-destructive way, the genetic nature of inclusions in diamond. With this aim, a diamond from the Udachnaya kimberlite, Siberia, was investigated. The diamond, previously studied by Nestola et al. (2011), has anomalous birefringence and the two largest olivines have typical “diamond-imposed” shapes. The study of the topographic images shows that the diamond exhibits significant deformation fields related to post growth plastic deformation. The absence of dislocations starting from the olivine inclusions, and the dark contrasts around them represent the main results obtained by XRDT, contributing to the elucidation of the relationships between the diamond and the olivines at the micron-meter scale. The dark halo surrounding the inclusions was likely caused by the effect of different thermo-elastic properties between the diamond and the inclusions. The absence of dislocations indicates that the diamond-imposed morphology did not produce the volume distortion commonly associated with the entrapment of the full-grown inclusions and, thus, only based on such evidence, a syngenetic origin could be proposed. In addition, stepped figures optically observed at the interface between diamond and one of the olivines suggest processes of selective partial dissolution that would contribute to a change in the final morphology of inclusions. These results show that a diamond morphology may be imposed to a full-grown (protogenetic) olivine during their encapsulation, suggesting that the bulk of the inclusion is protogenetic, whereas its more external regions, close to the diamond-inclusion interface, could be syngenetic.

Growth and post-growth defects in a diamond from Finsch mine (South Africa)

A diamond from the Finsch mine (South Africa) was investigated by X-ray diffraction topography to characterize the extended defects and to reconstruct the growth history. The sample was a doubly polished triangular diamond slice with a rounded side in which re-entrant corners could be seen and the specimen exhibited anomalous birefringence. X-ray topographs show that the sample is actually a mosaic crystal that developed through aggregation of sub-individual parts during growth: some slightly rotated relative to one another and others twinned. The twin law is by reticular merohedry and consists of the well-known 2-fold rotation around [111]. Micro-Raman spectroscopy data revealed that the main inclusions are pyrope and enstatite trapped in the inner part of the individual. No dislocations nucleated from the silicate inclusions. Growth-sector boundaries, dislocations, grain boundaries and twinning indicate that these features formed during the growth of diamond. Throughout the whole sample and chiefly in the regions showing a lower density of inclusions, packed lamination lines parallel to an octahedral face can be observed. These laminations represent a polysynthetic twinning commonly observed in diamonds which have undergone plastic deformation and are considered to be a post-growth defect. The analysis of the structural defects allows a reconstruction of a complex growth history, characterized by a sequence of alternating episodes of growth and dissolution and, lastly, plastic deformation. This study represents a methodological contribution to the studies on the origin of diamond.

Anomalous birefringence in andradite–grossular solid solutions: a quantum-mechanical approach

The static linear optical properties (refractive indices, birefringence and axial angle) of andradite–grossular (Ca3Fe2Si3O12–Ca3Al2Si3O12) solid solutions have been computed at the ab initio quantum-mechanical level through the Coupled Perturbed Kohn–Sham scheme, using an all-electron Gaussian-type basis set. Geometry relaxation after substitution of 1–8 Al for Fe atoms in the primitive cell of andradite yields 23 non-equivalent configurations ranging from cubic to triclinic symmetry. Refractive indices vary quite regularly between the andradite (1.860) and grossular (1.671) end-members; the birefringence δ and the axial angle 2V at intermediate compositions can be as large as 0.02° and 89°, respectively. Comparison with experiments suffers from inhomogeneities and impurities of natural samples; however, semi-quantitative agreement is observed.

Mathematical model of compensation for dispersion of light polarization states in electrooptical systems based on chiral liquid crystals

Spectral dispersion of the polarization states occurs after passage of linearly polarized light through a thin layer of a chiral nematic crystal along the helical axis. It is clearly pronounced for crystals with a high optical anisotropy and a helical pitch somewhat larger than the light wavelength. The results of numerical analysis of the spectral dependence of polarization states at the output of the liquid crystal layer and the method for compensating for the dispersion are presented for the first time. It is shown that polarization dispersion can be eliminated using phase plates of two types, one of which should have a high anomalous birefringence dispersion. The possibility of developing fast light modulators operating in a wide spectral range is discussed.

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.

Electric Birefringence of Dispersions of Platelets

This paper describes the electro-optic response of a suspension of disk-like colloids. We have considered aqueous suspensions of Gibbsite platelets and measured the electrically induced birefringence in the broad frequency range 10(2)-10(8) Hz. When simply dispersed in an electrolyte solution, these particles orient with their major axis parallel to the electric field at all frequencies. The spectral dependence of their Kerr coefficient features three regimes: an electrokinetic α-relaxation within the kHz range, a conductive Maxwell-Wagner-O'Konski (MWO) relaxation having characteristic frequency in the 1-10 MHz range, and a nonzero high frequency asymptote. We quantitatively analyze the MWO spectral component and the high-frequency asymptote on the basis of a model developed for oblate particles. This analysis enables us to obtain the relevant particle properties: surface conductivity, zeta potential, and intrinsic Gibbsite birefringence. When the particles are dispersed in a mixture that also contains smaller spherical particles that have a charge of the same sign, their electric birefringence becomes negative at low frequency. This anomalous orientation of the platelets is analogous to that observed in mixtures of prolate and spherical particles, and demonstrates the anomalous birefringence as a universal property of suspensions of nonspherical particles when surrounded by smaller charged particles.

Precursor dynamics in the ferroelectric phase transition of barium titanate single crystals studied by Brillouin light scattering

The acoustic anomalies and precursor dynamics of high-quality barium titanate single crystals were investigated by Brillouin light scattering and the birefringence measurements in the paraelectric phase above the cubic-to-tetragonal ferroelectric phase transition temperature (${T}_{c}$). Two elastic stiffness coefficients ${C}_{11}$ and ${C}_{44}$, the related sound velocities, and their absorption coefficients were determined from ${T}_{c}$ to 400${\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}$C for the first time. The longitudinal acoustic (LA) mode showed a substantial softening over a wide temperature range above ${T}_{c}$ which was accompanied by a remarkable increase in the acoustic damping as well as growth of central peaks. The broad central peak (CP) exhibited a two-mode and one-mode behavior in the paraelectric and ferroelectric phase, respectively, which was consistent with recent far-infrared reflectivity measurements and first-principle-based calculations [Ponomareva et al., Phys. Rev. B 77, 012102 (2008)]. The acoustic anomalies and CP behavior were correlated with the anomalous birefringence, piezoelectric effect, and the deviation of the Curie-Weiss law observed from the same crystal. This strongly indicates similarity between the dynamics of polar clusters in typical ferroelectrics and the dynamics of polar nanoregions in relaxors, consistent with recent acoustic emission measurements [Dul'kin et al., Appl. Phys. Lett. 97, 032903 (2010)]. The relaxation times estimated from the central peak and the LA mode anomalies exhibited similar temperature dependences with comparable orders of magnitude, indicating that the polarization fluctuations due to the precursor polar clusters couples to the LA mode through density fluctuations. All these anomalies share common microscopic origin, correlated Ti off-centered motions forming polar clusters having local symmetry breaking in the paraelectric phase. The existence of the polar clusters were directly evidenced by the temperature evolution of the precise birefringence map. The narrow central peak within $\ifmmode\pm\else\textpm\fi{}$5 GHz proposed before was not confirmed to exist in the present study.

Evidence of a circularly polarized light mode along the optic axis inc-cutNH4H2PO4, induced by circular differential reflection and anomalous birefringence

The anomalous birefringence and circular differential reflection ofNH4H2PO4 (point group ), cut on the optic axis, have been found to cause an additional signal in measurements ofthe optical rotation employing polarized light technology, with the sample betweencrossed and slightly modulated linear polarizers (tilting high accuracy universalpolarimetry). The azimuthal rotation of the linearly polarized light, up to 100times larger than expected, is described in terms of a circularly polarized lightmode along the optic axis of varying amplitude. Experimental evidence leadingto our conclusion is given and a qualitative model for the effect is presented.