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Exploring non π-conjugated phosphate birefringent crystal with a large birefringence has been a great challenge. Herein, based on the unique two-dimensional layered structure in KBe2 BO3 F2 (KBBF), two new compounds, Sn2 PO4 I and Sn2 BO3 I, were designed and synthesized successfully, maintaining the layer structural feature and enhancing the optical anisotropy of crystals. In particular, the birefringence of Sn2 PO4 I is larger than or equal to 0.664 @546 nm, which is largest among the reported borates and phosphates, even surpassing commercial birefringent crystals YVO4 and TiO2 . This work indicates that a breakthrough in birefringence of inorganic compound was achieved. Also, it provides a guiding idea for exploring large birefringence materials in the future.

Maximizing the optical anisotropy in birefringent materials has emerged as an efficient route for modulating the polarization-dependent light propagation. Currently, the generation of deep-ultraviolet (deep-UV) polarized light below 200 nm is essential but challenging due to the interdisciplinary significance and insufficiency of high-performing birefringent crystals. Herein, by introducing multiple heteroanionic units, the first sodium difluorodihydroxytriborate-boric acid Na[B3 O3 F2 (OH)2 ]⋅[B(OH)3 ] has been characterized as a novel deep-UV birefringent crystal. Two rare heteroanionic units, [B3 O3 F2 (OH)2 ] and [B(OH)3 ], optimally align to induce large optical anisotropy and also the dangling bonds are eliminated with hydrogens, which results in an extremely large birefringence and band gap. The well-ordered OH/F anions in [B3 O3 F2 (OH)2 ] and [B(OH)3 ] were identified and confirmed by various approaches, and also the origin of large birefringence was theoretically discussed. These results confirm the feasibility of utilizing hydrogen involved heteroanionic units to design crystals with large birefringence, and also expand the alternative system of deep-UV birefringent crystals with new hydroxyfluorooxoborates.

This research was financially supported by the National Natural Science Foundation of China (no. 51432006), the Ministry of Education of China for the Changjiang Innovation Research Team (no. IRT14R23), the Ministry of Education and the State Administration of Foreign Experts Affairs for the 111 Project (no. B13025), and the Innovation Program of Shanghai Municipal Education Commission. C.W. thanks the National and Shanghai Postdoctoral Program for Innovative Talents (nos. BX201800216 and 2018192). M.G.H. thanks the Australian Research Council for support (DP170100411).

The main commercially used birefringent oxides α-BaB2 O4 and YVO4 have the birefringences of 0.12 and 0.22. We propose a targeted high-throughput screening system to search birefringence-active functional modules (FMs) and large birefringent materials. A series of π-conjugated C-O units [C2 O4 ]2- , [C2 O6 ]2- , [C4 O4 ]2- , and [C6 O6 ]2- are discovered to be birefringence-active FMs. Theoretical and experimental studies on the crystals with C-O units confirm the feasibility of strategy. Based on this, the C-O containing compounds ranging from deep-ultraviolet to near-infrared region with large birefringence from 0.1 to 1.35 are found, and most of them break through the birefringent limit of oxides. The (NH4 )2 C2 O4 ⋅H2 O crystal is grown and its experimental birefringence is 0.248 at 546 nm, which is identified as a promising UV birefringent crystal. The A-site cations play significant roles in optical properties by influencing the density and arrangement of the C-O units.

Spectral methods have recently gained popularity in many domains of computer graphics and geometry processing, especially shape processing, computation of shape descriptors, distances, and correspondence. Spectral geometric structures are intrinsic and thus invariant to isometric deformations, are efficiently computed, and can be constructed on shapes in different representations. A notable drawback of these constructions, however, is that they are isotropic, i.e., insensitive to direction. In this paper, we show how to construct direction-sensitive spectral feature descriptors using anisotropic diffusion on meshes and point clouds. The core of our construction are directed local kernels acting similarly to steerable filters, which are learned in a task-specific manner. Remarkably, while being intrinsic, our descriptors allow to disambiguate reflection symmetries. We show the application of anisotropic descriptors for problems of shape correspondence on meshes and point clouds, achieving results significantly better than state-of-the-art methods.

Poly-3-hexylthiophene (P3HT) nanofibers are 1D crystalline structures with semiconductor properties. When P3HT nanofi bers are dispersed in nonconducting solvent, they react to external alternate e ...

© 2018 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Optical metamaterials offer the tantalizing possibility of creating extraordinary optical properties through the careful design and arrangement of subwavelength structural units. Gyroid-structured optical metamaterials possess a chiral, cubic, and triply periodic bulk morphology that exhibits a redshifted effective plasma frequency. They also exhibit a strong linear dichroism, the origin of which is not yet understood. Here, the interaction of light with gold gyroid optical metamaterials is studied and a strong correlation between the surface morphology and its linear dichroism is found. The termination of the gyroid surface breaks the cubic symmetry of the bulk lattice and gives rise to the observed wavelength- and polarization-dependent reflection. The results show that light couples into both localized and propagating plasmon modes associated with anisotropic surface protrusions and the gaps between such protrusions. The localized surface modes give rise to the anisotropic optical response, creating the linear dichroism. Simulated reflection spectra are highly sensitive to minute details of these surface terminations, down to the nanometer level, and can be understood with analogy to the optical properties of a 2D anisotropic metasurface atop a 3D isotropic metamaterial. This pronounced sensitivity to the subwavelength surface morphology has significant consequences for both the design and application of optical metamaterials.

Polarized microscopy provides unique information on anisotropic samples. In its most complete implementation, namely Mueller microscopy, this technique is well suited for the visualization of fibrillar proteins orientations, with collagen in the first place. However, the intrinsic optical anisotropy of unstained tissues has to be enhanced by Picrosirius Red (PR) staining to enable Mueller measurements. In this work, we compared the orientation mapping provided by Mueller and second harmonic generation (SHG) microscopies on PR stained samples of vaginal and uterine cervix tissues. SHG is a multiphoton technique that is highly specific to fibrillar collagen, and was taken as the "gold standard" for its visualization. We showed that Mueller microscopy can be safely used to determine collagen orientation in PR stained cervical tissue. In contrast, in vaginal samples, Mueller microscopy revealed orientations not only of col- lagen but also of other anisotropic structures. Thus PR is not fully specific to collagen, which necessitates comparison to SHG microscopy in every type of tissue. In addition to this study of PR specificity, we determined the optimal values of the staining parameters. We found that staining times of 5 min, and sample thicknesses of 5 mm were sufficient in cervical and vaginal tissues. Microsc. Res. Tech. 00:000-000, 2015. V C 2015 Wiley Periodicals, Inc.

We investigated the optical anisotropy properties of m-plane air/AlGaN distributed Bragg reflector microcavities fabricated by the thermal decomposition of GaN. Micro-photoluminescence measurements were performed at room temperature. From the recorded spectrum, two cavity modes with different polarization direction (parallel to a and c) were observed, which are attributed to the birefringence properties of the non-polar nitride structure. In addition, the mode with E ‖ a has a higher PL intensity than that of the mode with E ‖ c. Based on k · p Hamiltonians, the matrix elements were calculated around the Γ point, revealing the origin of the mode intensity difference. These results would be very helpful for exciton-cavity coupling research in non-polar microcavities. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Phase retardation ΔΦ values for the LC cells with homogeneous and inhomogeneous LC director distribution vs the LC pretilt angle θ0 on the cell's substrates, namely for hybrid cells with different LC pretilt angles at every substrate and films with negative optical anisotropy materials.

To resolve the long standing controversy between experimentally measured reflectance anisotropy (RA) of C(111)2 x 1 surface and theoretically calculated optical response, we demonstrated that defects at the C(111) surface in the form of minor hydrogen contamination, missing carbon atoms and/or terraces can be responsible for the appearance of the gap between the surface states, which is absent for the Pandey reconstructed ideal C(111)2 x 1. Ab initio DFT LDA calculations for such non-ideal systems indeed demonstrate that even 6% of residual hydrogen (which is below the standard experimental detection limits) or 40 angstrom wide terraces are enough to sufficiently open the surface gap and account for the observed optical anisotropy. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The influence of the polymer/fullerene blend ratio on the morphological properties of organic solar cells is investigated. Spectroscopic ellipsometry is applied as a tool for analyzing fullerene domains and the influence on polymer crystallinity within the film. Furthermore, the measurements are correlated with a percolation limit of as-cast films at around 40 wt% fullerene content.

We have successfully developed a novel compensation film, EVE-film Environmental friendly film for VA-LCD performance Enhancement, which improves VA-LCD performance with less environmental burden. We satisfactorily realized optical designs of EVE-film by controlling the internal haze, wavelength dispersion, and optical anisotropy, with innovative casting process. After all our efforts, VA-LCD using EVE-film exhibited 13% higher contrast and a color-shift significantly better than our previous compensation film.

Purpose: A theoretical model of biaxial optical anisotropy is derived and its structural, biomechanical and developmental implications are discussed with reference to known corneal anatomy. Methods: A concise review of the theory of optical crystallography is followed by the derivation of a theoretical model of the optical anisotropic properties of a dome of biaxial birefringent crystalline material. The model is then applied to parameters relevant to the biaxial model of human corneal birefringence. Results: Theoretical distributions of refractive indices and vibration directions for transmitted monochromatic light are derived for the central and paracentral zones of a model human cornea. Contours of equal refractive index (equirefringence curves) are found to have orthogonal confocal spheroconic geometry. Conclusions: A novel model of corneal structure is proposed in which discrete uniaxial positive birefringent fibre-like elements conform to the derived spheroconic geometry. Biomechanical implications and the relationship of the birefringent elements to known corneal anatomy are discussed. The crystallographic conventions are proposed as a standard for further investigations of corneal birefringence.

Optical anisotropy measurement is essential for material characterization and biological imaging. In order to achieve single-shot mapping of the birefringence parameters of anisotropic samples, a novel polarized light imaging concept is proposed, namely quantitative polarization interference microscopy (QPIM). QPIM can be realized through designing a compact polarization-resolved interference microscopy system that captures interferograms bearing sample’s linear birefringence information. To extract the retardance and the orientation angle maps from a single-shot measurement, a mathematical model for QPIM is further developed. The QPIM system is validated by measuring a calibrated quarter-wave plate, whose fast-axis orientation angle and retardance are determined with great accuracies. The single-shot nature of QPIM further allows to measure the transient dynamics of birefringence changes in material containing anisotropic structures. This application is demonstrated by capturing transient retardance changes in a custom-designed parallel-aligned nematic liquid crystal-based device.

Wurtzite A- and M-plane InN films were grown by molecular beam epitaxy (MBE) on free-standing GaN substrates. Spectroscopic ellipsometry (SE) in the photon energy range from 0.56 up to 15 eV was applied in order to determine the ordinary and extraordinary complex dielectric function (DF) of InN. A distinct optical anisotropy was found over the whole energy range. The extraordinary absorption edge in comparison to the ordinary one is shifted to higher energies confirming previous studies. The investigations in the upper vacuum-ultraviolet (VUV) spectral range (9.5–15 eV) yielded transition energies for four critical points (CPs) of the band structure (BS) which have not been observed so far.

First-principles calculations of the anisotropic optical response of Si(111)-(4 × 1)(8 × 2)-In from the mid-infrared to the visible region are compared with recent experimental data. The experimental data show that the anisotropic Drude tail of the (4 × 1) room-temperature phase is replaced by two peaks at 0.50eV and 0.72eV after the phase transition to the low-temperature (8 × 2) structure took place. The spectrum calculated from both intraband and interband transitions for the metallic zig-zag chain model of the (4 × 1) phase accounts well for the room-temperature data. The low-temperature data are well explained on the basis of the semiconducting hexagon (8 × 2) model by interband transitions mainly from a region close the high-symmetry line of the Brillouin zone (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We investigate anisotropic properties of strained InGaAs quantum wells on the high index (11n)A (n = 3,4,5) GaAs substrates. The polarization dependence of photoluminescence of strained InGaAs quantum wells were measured, and optical anisotropy was observed. We calculated anisotropy of the optical transition matrix elements based on the 4x4 and 6x6 Luttinger model for the quantum wells with uniaxial strain. The calculated anisotropy taking into account of split-off band qualitaively agree with our experiment. This indicates that the band mixing of split-off band into the heavy-hole band largely contributes to the the optical anisotropy in the strained InGaAs quantum wells on the high index substrates. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on a theoretical-experimental study of reflectance anisotropy spectroscopy (RAS) of GaAs (001) crystals under uniaxial stress. The study was carried out in the energy region around the fundamental transition. RAS spectra in the energy range from 1.2-1.7 eV were measured with a photoelastic-modulator-based spectrometer. To induce an optical anisotropy, the GaAs crystals were thinned down to 400 mm and an calibrated uniaxial stress was applied by deflection. RAS showed a line shape consisting of an oscillation at around E0. On the basis of a perturbative approach employing the Pikus-Bir Hamiltonian, we calculated the RAS line shape and found a close agreement with the experimental spectra. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The effects of La2O3 addition and PbO excess on the microstructures and optical properties of PbZrO3–PbTiO3–Pb(Zn1/3Nb2/3)O3 (PZ–PT–PZN) ceramics prepared by spark plasma sintering were investigated. When 1 mol% La2O3 was added, the highest transmittance of 35% at 700 nm for PZ–PT–PZN ceramics was obtained. The improved transmittance was attributed to the increased relative density and the decreased optical anisotropy. The samples containing more than 1 mol% La2O3 showed decreased transmittance, due to the appearance of secondary phases. The transmittance of PZ–PT–PZN ceramics increased slightly to 29% at 700 nm with increasing amount of excess PbO up to 10 mol% and thereafter decreased rapidly.

We have used polarized photoreflectance spectroscopy to study the electronic-band-structure modification of GaN films grown along different nonpolar orientations due to biaxial, anisotropic in-plane strain. For nonpolar oriented films, the c-axis of GaN lies in the film plane. In four different GaN films with a nonpolar orientation (M- and A-plane), we observe a large in-plane optical polarization anisotropy, which is much larger for the M-plane films due to the much larger strain in at least one of the in-plane directions. The experimental results for the transition energies and oscillator strengths are compared with theoretical results obtained using the k·p perturbation approach. The large optical polarization anisotropy in M-plane GaN films can be used for polarization filtering and polarization-sensitive photodetectors.

Light scattering, viscosity, and dilatometric studies of poly-β-vinylnaphthalene solutions indicate the conformational transformation in the macromolecule near 50–60°C. This transformation separates two states of the macromolecule, characterized by the different temperature coefficients of the partial specific volume dv/dT. The transformation is accompanied by a decrease of the optical anisotropy of the macromolecules. These phenomena can reflect disordering of the regular short sequences in the macromolecule or overcoming the barrier to the rotation of their naphthalene groups. It is possible to admit the coexistence of these two mechanisms in some cases.

By the method of light scattering, measurements were made on particles of polystyrene and polyvinylacetate latices. The angular distribution of the scattered light was measured and the partial Rayleigh ratios as well as the polarization ratios were determined. These values were measured as a function of the concentration and the measurements were extrapolated to the zero concentration. Values of the specific partial Rayleigh ratios (Hv:/c)₀ and (Vh/c)₀ proved to be significantly different from zero indicating the existence of the optical anisotropy of particles. The polarization ratio Dv was also found to be significantly different from zero. The optical anisotropy of polystyrene latices was found to be significantly higher than that of polyvinylacetate latices. This was ascribed to a structural anisotropy of the polymeric material within the particles. The hard polystyrene spheres show a small but existing degree of crystallinity, whereas the soft polyvinylacetate spheres, although having a finite anisotropy, show a vanishing degree of crystallinity.

We present comprehensive studies of in-plane optical anisotropy in CdSe/ZnSe quantum dot ensembles. The anisotropy reveals itself as circular-to-linear polarization conversion and as an alignment occurring at resonant excitation without any applied magnetic fields. The variation of the anisotropy in different dots has been analyzed based on angle scans. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The reflection anisotropy spectra of the noble metal (110) surfaces are discussed in terms of surface modified bulk transitions within the derivative model and derivative model parameters for a range of variously structured surfaces are presented. The utility and consistency of the derivative model in explaining noble metal spectra is demonstarted. RAS spectra of ion bombarded noble metal surfaces are explained in terms of roughness induced uncertainty in the electronic wavevectors in the surface region. Spectra of nanostructured Cu(110) surfaces are presented and discussed. Contrasting spectral evolution during annealing for the (110) and (771) surfaces is attributed to differing step densities. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

School of Physics and Centre for Materials Science and Engineering, University of Edinburgh, Edinburgh, EH9 3JZ, United Kingdom Received 5 June 2005, revised 4 August 2005, accepted 9 August 2005 Published online 29 November 2005 PACS 62.20.Fe, 78.20.Hp, 78.40.Kc The optical anisotropy of copper samples undergoing tensile testing is investigated using reflection anisot-ropy spectroscopy (RAS). The amplitudes of specific RAS spectral features are found to vary differently with strain, indicating sensitivity to distinct piezo-optic mechanisms.

Electronic structures and optical properties of wide-band-gap CaGa2S4 are investigated by using the sub-unit model systems and employing the first-principles calculation. Reflecting the arrangement of S-atom decahedron networks, there appear two one-dimentional parallel bands in higher valence bands, which are made of bonding and antibonding states of S-pz orbitals. These bands induce large optical anisotropy along the z direction and become the origin of two strong absorption-spectrum peaks observed in experiments. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical birefringence measurements for a calamitic lyotropic liquid crystal containing sodium lauryl sulphate/decanol/water are presented. A value of the order of 10-3 was obtained, much smaller than that of thermotropic liquid crystals. The order parameter temperature dependence is evaluated using an extrapolating method and taking into accounts the influence of the micelle shape. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Surface optical anisotropy of GaAs(001) is extremely sensitive to adsorption of electropositive and electronegative atoms. The oxygen-induced experimental changes of the reflectance anisotropy spectrum of the As-rich (2 × 4) surface are interpreted using ab initio calculations. We conclude that oxygen adsorption, contrary to previous beliefs, does not quench all surface-related optical transitions, but only those for which the initial state is surface-related. Alkali metal (AM) adsorption is found to induce a strong negative signal in the 3.5 eV–5 eV range, weakly dependent on surface reconstruction and AM nature, whose origin is discussed. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Self-assembling nanostructures comprising InGaAs quantum rods (QRs) immersed into 2-dimensional InGaAs layer (QW) were examined by photoreflectance (PR) and photoluminescence (PL) spectroscopy techniques. Spectral features associated with interband op- tical transitions occurring in the QR and the surrounding QW regions have been identified. The polarized PR and PL studies revealed a high in-plane optical anisotropy of ≈60% for QR-related optical transitions. We have clearly observed that both the QR- and the QW-related transition energies, and PL intensities are sensitive to the As source (As2 or As4) used in molecular beam epitaxy growth of the nanostructures. The changes in optical response are mainly attributed to carrier confinement effects caused by variation in indium content within the QR and QW regions. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)