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As an exceptional optical gene, the [PO4] tetrahedron is indispensable in the field of optical crystals due to its gain in the band gap of solid materials. However, the high symmetry of [PO4] tetrahedron hinders the achievement of large optical anisotropy in the lattice for phosphate crystal forms. In this work, the heteroleptic tetrahedra strategy, which involves replacing some of the oxygen atoms on regular oxy‐tetrahedra, is proven to be a feasible approach for preserving the wide transmission of the original [PO4] tetrahedra and improving the polarizability anisotropy. Based on this, eight methylphosphates are designed and synthesized for the phosphate system by substituting a [CH3] group for the O atom on the [PO4] tetrahedra. Theoretically, as compared to [PO4] units, [CH3PO3] and [CH3PO3H] units can improve the polarizability anisotropy, particularly [CH3PO3H] units, which have the potential to be birefringence‐active. The strong birefringence (exp. 0.108@546.1 nm) and short deep‐UV cutoff edge (195 nm) of nonmetallic methylphosphates [C(NH2)3][CH3PO3H] in the series suggest that it may be a possible short‐wave UV birefringent crystal. In addition to providing new birefringence‐active units for optical material design, this study validates the viability of modifying tetrahedra to improve inherent short board of nearly rigid [PO4] tetrahedra in phosphate family. [ABSTRACT FROM AUTHOR]

Polarized light is critical for a wide range of applications in modern optics. However, its generation and modulation typically require additional optical comments, which hinders device compactness. Herein, an air‐stable Tin(IV)‐based hybrid metal halide, (C10H9N2O)2SnCl6, composed of [C10H9N2O]+ cations and isolated [SnCl6]2− octahedra is reported. Notably, (C10H9N2O)2SnCl6 exhibits a robust birefringence of 0.50@550 nm that is evidently larger than those of commercially used crystals, which enables efficient modulation of polarized light. Moreover, it possesses a broad polarized blue emission in the range of 374–600 nm with a peak at 426 nm. Theoretical and structural studies reveal that the high optical anisotropy for large birefringence and directly polarized emission of (C10H9N2O)2SnCl6 is ascribed to the cooperative effect of distortion of [SnCl6]2− and high π‐conjugation of [C10H9N2O]+ in parallel arrangement. This work may provide new thoughts on designing and realizing the miniaturization of polarization‐resolved optoelectronic devices. [ABSTRACT FROM AUTHOR]

Porous semiconductors have garnered significant attention owing to their distinctive physical and chemical properties. In this study, optical anisotropy is presented in porous germanium (PGe) on a Si (001) substrate. Both n‐ and p‐type PGe, achieved through bipolar electrochemical etching, exhibit optical anisotropy along the Ge <001> direction, as determined by spectroscopic ellipsometry. Birefringence and depolarization factors are controllable by adjusting the etching parameters and doping concentration of the epitaxial Ge layer. The gradient porosity and pore distribution in PGe can be well captured by the optical models. The findings of optical anisotropy in PGe‐on‐Si hold promise for applications in optical elements or sensors for gas or biomolecules. [ABSTRACT FROM AUTHOR]

Tetrahedral oxygenated groups with large highest occupied molecular orbital‐lowest unoccupied molecular orbital (H gaps such as [SO4] are beneficial for deep ultraviolet (DUV) transmission but usually make against generating sufficient birefringence due to the small polarizability anisotropy. Thus, it is extremely difficult to obtain DUV transmission and large birefringence simultaneously in the search for DUV birefringent materials in sulfates. Herein, two new ammonium‐rare earth metal sulfates, NH4Y(SO4)2·H2O and NH4YSO4F2, with DUV transmission are presented. Meanwhile, both exhibit greatly elevated birefringence through the involvement of NH4+ units, compared to Y2(SO4)3·8H2O. Their optical properties are further investigated by theoretical calculations, and the effect of the introduction of NH4+ into yttrium sulfate on optimizing the structures and properties is discussed. This work may provide a new perspective for further exploration of DUV birefringent materials in tetrahedral oxygenated group sulfates. [ABSTRACT FROM AUTHOR]

Materials with large birefringence (Δn, where n is the refractive index) are sought after for polarization control (e.g., in wave plates, polarizing beam splitters, etc.), nonlinear optics, micromanipulation, and as a platform for unconventional light-matter coupling, such as hyperbolic phonon polaritons. Layered 2D materials can feature some of the largest optical anisotropy; however, their use in most optical systems is limited because their optical axis is out of the plane of the layers and the layers are weakly attached. This work demonstrates that a bulk crystal with subtle periodic modulations in its structure-Sr9/8 TiS3 -is transparent and positive-uniaxial, with extraordinary index ne = 4.5 and ordinary index no = 2.4 in the mid- to far-infrared. The excess Sr, compared to stoichiometric SrTiS3 , results in the formation of TiS6 trigonal-prismatic units that break the chains of face-sharing TiS6 octahedra in SrTiS3 into periodic blocks of five TiS6 octahedral units. The additional electrons introduced by the excess Sr form highly oriented electron clouds, which selectively boost the extraordinary index ne and result in record birefringence (Δn > 2.1 with low loss). The connection between subtle structural modulations and large changes in refractive index suggests new categories of anisotropic materials and also tunable optical materials with large refractive-index modulation.

The combination of rigid (AlO 6) and deformable (MoO 6 and TeO 3) groups leads to a robust birefringent crystal (Al 2 Te 2 MoO 10) for compact optical polarization components which could efficiently divide one incident light into two polarized beams. [Display omitted] There is a pressing demand for the development of novel birefringent crystals tailored for compact optical components, especially for crystals exhibiting large birefringence across a range of temperatures. This has commonly been achieved by introducing various deformable groups with high polarizability anisotropy. In this study, we combined both rigid and deformable groups to synthesise a new birefringent crystal, Al 2 Te 2 MoO 10 , which demonstrates an exceptional birefringence value of 0.29@550 nm at room temperature. Not only is this higher birefringence than that of commercial crystals, but Al 2 Te 2 MoO 10 exhibits excellent birefringence stability over a wide temperature range, from 123 to 503 K. In addition, the first-principles theory calculations and structural analyses suggest that although the rigid AlO 6 groups do not make much contribution to the prominent birefringence, they nonetheless played a role in maintaining the structural anisotropy at elevated temperatures. Based on these findings, this paper proposes a novel structural design strategy to complement conventional approaches for developing optimal birefringent crystals under various environmental conditions. [ABSTRACT FROM AUTHOR]

Combining π‐conjugated and non‐π‐conjugated groups is an important strategy for synthesizing new nonlinear optical (NLO) crystals. However, the second harmonic generation (SHG) response and optical anisotropy can be limited by improper spatial alignment of these functional groups in the crystal structure. In this work, it is revealed that non‐π‐conjugated [NH2SO3] group acts as both hydrogen bond donor and acceptor, effectively regulating the 2D planar structure formed by π‐conjugated [C4N3H6] groups. The resulting organic–inorganic hybrid crystal C4N3H6SO3NH2 exhibits a strong SHG response (2.5 × KDP), large optical anisotropy (0.233@546 nm), and blue‐violet and green fluorescence near 360 and 520 nm, respectively. This work expands the methodology for creating new NLO crystals through organic–inorganic hybridization, while also showcasing the potential of C4N3H6SO3NH2 as a multifunctional optical material. [ABSTRACT FROM AUTHOR]

Our work uses a polarization matrix formalism to analyze and algorithmically represent optical anisotropy by open dehydration of blood plasma films. Analytical relations for Jones matrix reconstruction of optical birefringence maps of protein crystal networks of dehydrated biofluid films are found. A technique for 3D step-by-step measurement of the distributions of the elements of the Jones matrix or Jones matrix images (JMI) of the optically birefringent structure of blood plasma films (BPF) has been created. Correlation between JMI maps and corresponding birefringence images of dehydrated BPF and saliva films (SF) obtained from donors and prostate cancer patients was determined. Within the framework of statistical analysis of layer-by-layer optical birefringence maps, the parameters most sensitive to pathological changes in the structure of dehydrated films were found to be the central statistical moments of the 1st to 4th orders. We physically substantiated and experimentally determined the sensitivity of the method of 3D polarization scanning technique of BPF and SF preparations in the diagnosis of endometriosis of uterine tissue. [ABSTRACT FROM AUTHOR]

Sulfate crystals typically exhibit minimal optical anisotropy due to the near‐zero polarizability anisotropy (δ) of [SO4]2− tetrahedra, arising from highly symmetrical electron clouds. Recent research sought to enhance δ via chemical modifications, such as fluorination. However, the resultant crystals often maintain subpar optical anisotropy, frequently with birefringence values below 0.1. In this study, we have uncovered that δ can be significantly strengthened by chemically tailoring the tetrahedral [SO4]2− with anisotropic π‐conjugated modules. This has been demonstrated by several newly proposed S−O‐Org (Org: π‐conjugated organic species) moieties, which show a sharp increase in δ based on theoretical computations. To further validate this experimentally, we synthesized and characterized six new 3‐pyridinesulfonate crystals with the formula A(3‐C5H4NSO3) ⋅ xH2O (A=Li, Ag, K, Rb, Cs, and NH4; x=0 and 1). Notably, these materials exhibit strong optical anisotropy, with birefringence values ranging from 0.240 to 0.312 at 546 nm. These values are approximately 23 to 145.5 times greater than those of corresponding sulfates, and they outperform a vast number of sulfate‐related optical materials, thus verifying the effectiveness of the proposed strategy. Furthermore, the title compounds exhibit diverse microstructure peculiarities influenced by the size and binding natures of the counter cations. [ABSTRACT FROM AUTHOR]

A brief theoretical description of the processes of forming polarization maps of the azimuth and ellipticity of the multiple scattered component of the object field of the muscle tissue biopsy of rat stab wounds is presented. A series of polarization maps of ellipticity of digital microscopic images of the biopsy field of damaged and regenerated muscle tissue of rat stab wounds was obtained using the Muller-matrix Stokes polarimetry method. A wavelet transformation of polarization maps of ellipticity of digital microscopic images of the biopsy field of damaged and regenerated muscle tissue of rat stab wounds was implemented. Statistical, correlational and fractal wavelet markers for detecting the degree of regeneration of damaged biological tissues have been determined. Directions for further research by applying the principles of laser-induced autofluorescence polarimetry are given. [ABSTRACT FROM AUTHOR]

Birefringent crystals that can switch light polarization have important applications in optoelectronics. In the last decades, birefringence is mostly optimized by chemical strategies. Recently, switching birefringence by physical means has attracted much attention. Here, this work reports the observation of heat switching birefringence in a 2D layered hybrid halide perovskite (C2N3H4)2PbCl4 ((C2N3H4)+=1,2,4‐triazolium). This heat switching birefringence leads to a significant change in the interference color for the crystal plate under the illumination of orthogonal polarized light. Structure analyses reveal a heat dependent structure transition in (C2N3H4)2PbCl4, whose birefringence is switched by the change in the distortion degree of PbCl6 octahedron. This discovery may be beneficial to the further development of stimuli‐responsive polarization optical devices. [ABSTRACT FROM AUTHOR]

For traditional birefringent materials, the anion groups play the leading role in birefringence, while the alkali‐metal and alkaline‐earth‐metal cations are nearly inactive. This work proposes a strategy to activate the functions of the cation groups and uses the hydroxyborate systems for illustration. The experimental verification is carried out in the same anionic frame by replacing the traditional metal cations with the birefringence‐active units including planar groups of protonation [C(NH2)3], [C3N2H5], and [CN4H7]. The structures of four new hydroxyborates, α‐Rb2[B4O5(OH)4]·H2O, β‐Rb2[B4O5(OH)4]·H2O, [C(NH2)3]2[B4O5(OH)4]·H2O, and (CN4H7)B5O6(OH)4 are obtained for the first time, and [C(NH2)3]2[B4O5(OH)4]·H2O exhibits a markedly enlarged birefringence, which is about 2.75 times that of α‐Rb2[B4O5(OH)4]·H2O theoretically because the activated cations appear. This strategy breaks the dominant status of anions in the design of UV/deep ultraviolet materials with large birefringence and has significant implications for the rational design and discovery of materials with large birefringence in the future. [ABSTRACT FROM AUTHOR]

Birefringent crystals could modulate the polarization of light and are widely used as polarizers, waveplates, optical isolators, etc. To date, commercial birefringent crystals have been exclusively limited to purely inorganic compounds such as α‐BaB2O4 with birefringence of about 0.12. Herein, we report a new hydrogen bonded supramolecular framework, namely, Cd(H2C6N7O3)2⋅8 H2O, which exhibits exceptionally large birefringence up to about 0.60. To the best of our knowledge, the birefringence of Cd(H2C6N7O3)2⋅8 H2O is significantly larger than those of all commercial birefringent crystals and is the largest among hydrogen bonded supramolecular framework crystals. First‐principles calculations and structural analyses reveal that the exceptional birefringence is mainly ascribed to strong covalent interactions within (H2C6N7O3)− organic ligands and the perfect coplanarity between them. Given the rich structural diversity and tunability, hydrogen bonded supramolecular frameworks would offer unprecedented opportunities beyond the traditional purely inorganic oxides for birefringent crystals. [ABSTRACT FROM AUTHOR]

It is important to establish and clarify the relationship between stereochemically active lone pairs and birefringence, since it is one of the significantly effective routes to explore birefringent crystals by introducing Sn‐centered polyhedra with stereochemically active lone pairs. Herein, four tin(II)‐based ternary halides A3SnCl5 and ASn2Cl5 (A=NH4 and Rb) have been synthesized successfully. The experimental birefringence of Rb3SnCl5 and RbSn2Cl5 is larger than or equal to 0.046 and 0.123@546 nm, respectively. Through investigating the alkali or alkaline‐earth metal tin(II)‐based ternary halides, the structure‐performance relationship has been concluded between stereochemically active lone pairs and optical anisotropy. It is beneficial to the analysis and prediction of birefringence in tin‐based halides and provides a guide for exploring tin(II)‐based optoelectronic functional materials. [ABSTRACT FROM AUTHOR]

Collagenous tissues exhibit anisotropic optical properties such as birefringence and linear dichroism (LD) as a result of their structurally oriented supraorganization from the nanometer level to the collagen bundle scale. Changes in macromolecular order and in aggregational states can be evaluated in tendon collagen bundles using polarization microscopy. Because there are no reports on the status of the macromolecular organization in tendon explants, the objective of this work was to evaluate the birefringence and LD characteristics of collagen bundles in rat calcaneal tendons cultivated in vitro on substrates that differ in their mechanical stiffness (plastic vs. glass) while accompanying the expected occurrence of cell migration from these structures. Tendon explants from adult male Wistar rats were cultivated for 8 and 12 days on borosilicate glass coverslips (n = 3) and on nonpyrogenic polystyrene plastic dishes (n = 4) and were compared with tendons not cultivated in vitro (n = 3). Birefringence was investigated in unstained tendon sections using high-performance polarization microscopy and image analysis. LD was studied under polarized light in tendon sections stained with the dichroic dyes Ponceau SS and toluidine blue at pH 4.0 to evaluate the orientation of proteins and acid glycosaminoglycans (GAG) macromolecules, respectively. Structural remodeling characterized by the reduction in the macromolecular orientation, aggregation and alignment of collagen bundles, based on decreased average gray values concerned with birefringence intensity, LD and morphological changes, was detected especially in the tendon explants cultivated on the plastic substrate. These changes may have facilitated cell migration from the lateral regions of the explants to the substrates, an event that was observed earlier and more intensely upon tissue cultivation on the plastic substrate. The axial alignment of the migrating cells relative to the explant, which occurred with increased cultivation times, may be due to the mechanosensitive nature of the tenocytes. Collagen fibers possibly played a role as a signal source to cells, a hypothesis that requires further investigation, including studies on the dynamics of cell membrane receptors and cytoskeletal organization, and collagen shearing electrical properties. [ABSTRACT FROM AUTHOR]

The polarization modulation of deep‐UV light is an important process that incorporates functionality to selectively respond to light‐mater interaction. Typically, optical anisotropy is foremost to the use efficiency of deep‐UV birefringent crystals. Herein, a new congruently melting polyborate with extremely large birefringence (Δn(001)=0.14@589.3 nm) and band gap (6.89 eV) is discovered as a high performance birefringent crystal, which breaks the current deadlock of deep‐UV polyborates that usually show small birefringence. The rigid tetrahedra, including [ZnO4] and edge‐sharing [BO4] tetrahedra, make all the planar [BO3] triangles in the lattice adopt preferential arrangement and thereby lead to an extraordinary large birefringence that is larger than all the deep‐UV borates with experimentally measured values. Structural analyses with the additional theoretical calculations were used to study the origin of strong optical anisotropy in BaZnB4O8. [ABSTRACT FROM AUTHOR]

The effect of birefringence in anisotropic materials has been a long‐term issue for polarized Raman scattering. In this work, the polarization‐dependent Raman scattering in anisotropically birefringent materials is modeled with birefringence considered in the fundamental polarization selection rule. The birefringence‐induced polarization transformation is treated as a tensor in the calculation of Raman scattering intensity. The validity of this theory is further demonstrated in experiments by taking angle‐resolved polarized Raman measurements on the basal and cross planes of α‐MoO3—a typical biaxial van der Waals crystal with strong in‐plane and out‐of‐plane anisotropy. The anomalous angular dependency of polarized Raman scattering intensity can be well reproduced by the modified theoretical model with fitted real‐valued Raman tensors and birefringence‐related parameters. It can be concluded that this work can provide a valuable reference and guidance for quantitative analyses of anisotropic materials by using polarization‐resolved Raman scattering spectroscopy. [ABSTRACT FROM AUTHOR]

The effect of birefringence in anisotropic materials has been a long‐term issue for polarized Raman scattering. In this work, the polarization‐dependent Raman scattering in anisotropically birefringent materials is modeled with birefringence considered in the fundamental polarization selection rule. The birefringence‐induced polarization transformation is treated as a tensor in the calculation of Raman scattering intensity. The validity of this theory is further demonstrated in experiments by taking angle‐resolved polarized Raman measurements on the basal and cross planes of α‐MoO3—a typical biaxial van der Waals crystal with strong in‐plane and out‐of‐plane anisotropy. The anomalous angular dependency of polarized Raman scattering intensity can be well reproduced by the modified theoretical model with fitted real‐valued Raman tensors and birefringence‐related parameters. It can be concluded that this work can provide a valuable reference and guidance for quantitative analyses of anisotropic materials by using polarization‐resolved Raman scattering spectroscopy. [ABSTRACT FROM AUTHOR]

First-principle calculations are carried out to explore magnesium composition-dependent structural and optoelectronic features of wurtzite MgxZn1−xSe ternary alloys. Analyses show a nearly linear enhancement in lattice constants (a0, c0) but a reasonably nonlinear reduction in bulk modulus (B0) with increasing Mg composition. Successive incorporation of Mg atom(s) in place of Zn in the w-ZnSe crystal results in three direct-band gap (Γ–Γ) semiconductor ternary alloys. The fundamental band gap shows fairly nonlinear enhancement with increasing Mg composition. Each of the considered wurtzite specimens is optically anisotropic. The computed components of the refractive index give uniaxial birefringence. Peaks in the dielectric function spectrum of all the specimens in the ultraviolet (UV) region are contributed exclusively or collectively by Se-4p to Mg-4s, 3p and Zn-5s, 4p electronic excitations. With the enhancement in the fundamental band gap, static optical constants ε1(0), n(0) and R(0) of the specimens reduce, while critical point energy in their ε2(ω), k(ω), σ(ω), α(ω) spectra enhances. [ABSTRACT FROM AUTHOR]

Polarization sensitive optical coherence tomography (PSOCT) has been shown to image and delineate white matter fibers in a label-free manner by revealing optical birefringence within the myelin sheath using a microscope setup. In this proof-of-concept study, we adapt recent advancements in endoscopic PSOCT to perform depth-resolved imaging of white matter structures deep inside intact porcine brain tissue ex-vivo, through a small, rotational fiber probe. The probe geometry is comparable to microelectrodes currently used in neurosurgical interventions. The presented imaging system is mobile, robust, and uses biologically safe levels of optical radiation making it well suited for clinical translation. In neurosurgery, where accuracy is imperative, endoscopic PSOCT through a narrow-gauge fiber probe could provide intra-operative feedback on the location of critical white matter structures.

[Display omitted] • The α-MoO 3 ′s optical anisotropy is highly tunable under in-plane strain; • The |Δ n | max of strained α-MoO 3 is 0.288 @ 509 nm, which is 436% to that of unstrained one; • Increase of Δ n under strain comes from the ionic dipole moment of strained α-MoO 3 ; • The starting operation wavelength λ s under in-plane strain is also highly tunable; • The bandgap E g of strained α-MoO 3 has a dominate effect on the strain-modulating λ s. Strain offers a degree of freedom to realize the adjustability and enhancement of optical anisotropy. Herein, we theoretically and comprehensively investigate the tunable optical anisotropy and multiplied-enhancement birefringence of α-MoO 3 under in-plane strain, and further reveal the strain modulation mechanism by band structure and dipole moment of strained α-MoO 3. We find the optical anisotropy of strained α-MoO 3 is highly tunable. The starting operation wavelength λ s and the birefringence Δ n descend under a -axis strain and ascend under c -axis strain, and under biaxial strain they fall within the range of their counterparts under a -axis and c -axis strain. We also find the |Δ n | max is 0.288 @ 509 nm, whose percent ratio to that of unstrained α-MoO 3 is as high as 436%. Besides, the λ s is extended to approach the UV region by the c -axis compressive strain. The band structure results indicate bandgap E g plays a dominate role in determining the strain-modulating λ s , and the enhancement of Δ n of strained α-MoO 3 originates from the contribution of ionic dipole moment. The strained α-MoO 3 can make device tunable and vastly improve the its performance, and the proposed calculation method and strain modulation mechanism in this paper can be extended to other optically anisotropic and birefringent materials. [ABSTRACT FROM AUTHOR]

Birefringent crystals that can modulate the polarization of light play a significant role in modern optical devices including polarizing microscopes, optical isolators, and achromatic quarter‐wave plates. To date, commercial birefringent crystals are exclusively limited to purely inorganic compounds. Here we report a new organic–inorganic hybrid halide, MLAPbBr4 (MLA=melamine), which features a (110)‐oriented layered perovskite structure. Although the 6s2 lone‐pair electrons of Pb2+ cations are stereochemically inert, MLAPbBr4 exhibits a birefringence of 0.322@550 nm, which exceeds those of all commercial birefringent crystals. The first‐principles calculations reveal that this birefringence should be ascribed to the highly dislocated π‐conjugation of MLA cations and high distortion of PbBr6 octahedra. This work highlights the persistently neglected great potential of hybrid halide perovskites as birefringent crystals. [ABSTRACT FROM AUTHOR]

The possibilities of the diagnostic use of the singular approach of the distributions of the number of characteristic values of the MMI is effective for differentiating the polarization properties of histological biopsy sections of benign and malignant tumours of the uterus and prostate. Within the framework of evidence-based medicine, the sensitivity, specificity and accuracy of the azimuthal-invariant express (∼15 min) method of Mueller-matrix mapping of polarization-singular states in the differential diagnosis of uterine myoma and adenocarcinoma, as well as adenocarcinoma of the prostate with varying degrees of differentiation have been determined.

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 KBe2BO3F2 (KBBF), two new compounds, Sn2PO4I and Sn2BO3I, were designed and synthesized successfully, maintaining the layer structural feature and enhancing the optical anisotropy of crystals. In particular, the birefringence of Sn2PO4I 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. [ABSTRACT FROM AUTHOR]

Selenite crystalline materials have been popular owing to the diverse structures and optical performances. A new mercury selenite, MgHg(SeO 3) 2 (H 2 O) 2 , was synthesized by using a conventional hydrothermal method. It crystallizes in the monoclinic structure with a C 2/ c space group, MgHg(SeO 3) 2 (H 2 O) 2 exhibits a three-dimensional (3 D) structure, which is made up of [Hg(SeO 3) 2 ]2– ∞ chains and distorted MgO 4 (H 2 O) 2 octahedra. Besides, it presents a large birefringence of 0.137 @ 546 nm according to experimental measurement. Synthesis, crystal structure, thermal stability, optical property measurements and theoretical studies were performed in this work. A new magnesium mercury selenite has been successfully obtained by mild hydrothermal method with large birefringence of 0.137 @ 546 nm according to experimental measurement. [Display omitted] • Structurally, [HgO 6 ] and [SeO 3 ] units forming a one-dimensional {[Hg(SeO 3) 2 ]2-} ∞ anionic chains and form the overall three-dimensional (3D) framework with distorted MgO 4 (H 2 O) 2 octahedra. • MgHg(SeO 3) 2 (H 2 O) 2 presents a large birefringence of 0.137 @ 546 nm according to experimental measurement, while exists 0.148 @ 546 nm carried out through the first-principle calculations. • The experimental band gap of MgHg(SeO 3) 2 (H 2 O) 2 is 4.05 eV, which is relatively large in the whole selenite system. [ABSTRACT FROM AUTHOR]

Mid-infrared reflection spectra of c- and m-plane bulk AlN show a reststrahlen band related to the formation of phonon polaritons. However, it is worth noting that there are additional hump- and spike-shaped peaks in the spectra, which cannot be explained by the phonon-polaritons model applicable to optically isotropic crystals. Here, considering the existence of quasiphonons in wurtzite crystals, we suppose that the extra peaks result from the generation of quasiphonon polaritons (QPPs) induced by the coupling between photon and quasi-transverse optical phonon. On the basis of this point, a QPPs model applicable to optically anisotropic wurtzite crystals is developed, which successfully explains the reststrahlen band of bulk AlN. Besides, on the ground of our model, a series of reststrahlen band of bulk AlN under various configurations is also predicted and presented.

The main commercially used birefringent oxides α‐BaB2O4 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 [C2O4]2−, [C2O6]2−, [C4O4]2−, and [C6O6]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)2C2O4⋅H2O 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. [ABSTRACT FROM AUTHOR]

Diffraction optical elements (DOE) are important elements of systems for images displaying and processing. The DOE materials with both positive and negative birefringence enhance performances and functionality of such systems. We have calculated diffraction of rays passing through (OAGSM) by using our original Exedeep software. At the first time the diffraction parameters for both transmitted and reflected TE‐ and TM‐waves are calculated for materials with both positive and negative optical anisotropy. The simulation results are to be used to create DOE for visible, IR and THz range. [ABSTRACT FROM AUTHOR]

Since recently, a number of innovative polarization-based optical imaging modalities have been introduced and extensively used in various biomedical applications, with an ultimate aim to attain the practical tool for the optical biopsy and functional characterization of biological tissues. The techniques utilize polarization properties of light and Mueller matrix mapping of microscopic images of histological sections of biological tissues or polycrystalline films of biological fluids. The main drawback of currently developed laser polarimetry approaches and Mueller matrix mapping techniques is poor reproducibility of experimental data. This is due to azimuthal dependence of polarization and ellipticity values of most matrix elements to sample orientation in respect to incidence light polarization. Current study aims to generalize the methods of laser polarimetry for diagnosis of partially depolarizing optically anisotropic biological tissues. A method of differential Mueller matrix mapping for reconstruction of linear and circular birefringence and dichroism parameter distributions of partially depolarizing layers of biological tissues of different morphological structure is introduced and practically implemented. The coordinate distributions of the value of the first-order differential matrix elements of histological sections of brain tissue with spatially structured, optically anisotropic fibrillar network, as well as of parenchymatous tissue of the rectum wall with an "islet" polycrystalline structure are determined. Within the statistical analysis of polarization reproduced distributions of the averaged parameters of phase and amplitude anisotropy, the significant sensitivity of the statistical moments of the third and fourth orders to changes in the polycrystalline structure of partially depolarizing layers of biological tissue is observed. The differentiation of female reproductive sphere connective tissue is realized with excellent accuracy. The differential Mueller matrix mapping method for reconstruction of distributions of linear and circular birefringence and dichroism parameters of partially depolarizing layers of biological tissues of different morphological structures is proposed and substantiated. Differential diagnostics of changes in the phase (good balanced accuracy) and amplitude (excellent balanced accuracy) of the anisotropy of the partially depolarizing layers of the vagina wall tissue with prolapse of the genitals is realized. The maximum diagnostic efficiency of the first-order differential matrix method was demonstrated in comparison with the traditional methods of polarization and Mueller matrix mapping of histological sections of light-scattering biological tissues. [ABSTRACT FROM AUTHOR]

The synthetic red azo dye Ponceau 4R is an additive with widely utilization in food processing technology. Thermal behavior of the trisodium (8Z)-7-oxo-8-[(4-sulfonatonaphthalen-1-yl)hydrazinylidene] naphthalene-1,3-disulfonate, appointed Ponceau 4R or E124, was studied. Thermal analysis measurements of Ponceau 4R revealed thermal stability until 300 °C. Ponceau 4R is an anisotropic crystalline dye that has the property of birefringence. The THz spectroscopy allowed the determination of the characteristic absorption frequencies of this colorant and its identification in any food. In the THz spectrum of Ponceau 4R, it can be seen that the strongest absorption is produced for the radiation with frequency of 1.41, 1.74 and 3.81 THz. THz spectroscopy of Ponceau 4R identified spectral "signatures" of azo food dye studied, which were obtained by the processing of the numerical data of THz spectroscopy. [ABSTRACT FROM AUTHOR]

Keywords: Birefringence; Optical Anisotropy; Sulfate Crystals; TetrahedraA design strategy for significantly enhancing the polarizability anisotropy of isotropic tetrahedra in sulfate crystals is reported by Zhiyong Bai and Kang Min Ok in their Research Article (e202315311). This strategy involves chemically alternating tetrahedral [SO4]2− units with π‐conjugated organic groups. Experimental validation of the approach utilized 3‐pyridinesulfonate anion functional building blocks for crystal synthesis...By Zhiyong Bai and Kang Min OkReported by Author; Author [Extracted from the article]

Keywords: Birefringence; Optical Anisotropy; Sulfate Crystals; TetrahedraA design strategy for significantly enhancing the polarizability anisotropy of isotropic tetrahedra in sulfate crystals is reported by Zhiyong Bai and Kang Min Ok in their Research Article (e202315311). This strategy involves chemically alternating tetrahedral [SO4]2− units with π‐conjugated organic groups. Experimental validation of the approach utilized 3‐pyridinesulfonate anion functional building blocks for crystal synthesis...By Zhiyong Bai and Kang Min OkReported by Author; Author [Extracted from the article]

We report experimental results on the structure, refractive indices and birefringence of LiNaSO4 (LSS) crystals. Spectral behaviours of the refractive indices and the birefringence of LSS at the room temperature, as well as temperature and baric dependences of the birefringence are discussed. We examine the refractive indices and the birefringence using Lorentz-Lorenz and simplified Sellmeier formulae and energy-band structure calculations. Unlike LiKSO4, the birefringence of LSS decreases with increasing temperature, while accidental optically isotropic states are absent under the normal conditions. A significant increase in the birefringence of LSS, if compared with LiKSO4, is assumed to be linked with asymmetry appearing in the local second-coordination environment of the LSS structure. [ABSTRACT FROM AUTHOR]

PbMS 3 (M = Hf, Zr) are ternary sulfides with the general structure ABX 3 , where A is a metal, B is a transition metal and X is a chalcogen or halogen element. This work investigates the anisotropy of the optical and electronic properties of PbMS 3 , and their applicability in optoelectronic devices using first principles DFT calculations. PbHfS 3 is an indirect bandgap semiconductor (1.2 eV), whereas PbZrS 3 has direct bandgap (1.1 eV). The effective masses of electrons and holes exhibit strong anisotropy along the various high symmetry directions of the Brillouin zone. Important optical parameters are found to be strongly dependent on the direction of the incident radiation, best indicated by the large birefringence value. Considerable optical anisotropy suggests their promising linear and nonlinear optoelectronic applications such as polarizers, wave plates, and phase-matching elements. Small carrier effective masses, large charge recombination rates and suitable bandgap indicate the possibility of solar and photovoltaic applications. • The anisotropy of quasi-1D PbMS 3 materials are investigated using DFT. • The calculated results are in excellent agreement with the experiments. • The direct and indirect nature of the band structure is explained in detail. • PbMS 3 materials exhibit good electronic and optical anisotropy. • PbMS 3 materials are suitable for optoelectronic and photovoltaic applications. [ABSTRACT FROM AUTHOR]

In this work we have grown single crystals Kx(NH4)2-xSO4 (x ~1.75), which belong to a potassium-ammonium sulfate family, and studied their room- temperature structure. Spectral dependences of the principal refractive indices and principal optical birefringences are measured in the visible region. Anomalous birefringence dispersion is observed along the light propagation direction parallel to the principal x axis. According to our birefringence extrapolation based on the Sellmeier fit for the refractive indices, the symmetry of optical indicatrix at the room temperature should increase at the light wavelength λIP ≈ 1350±60 nm. This corresponds to a specific 'isotropic point' defined by the condition nx(λIP) = ny(λIP), which has not been detected in either K2SO4 or (NH4)2SO4 crystals [ABSTRACT FROM AUTHOR]

An interferential method is used for determining the linear birefringence of the thin polymer foils. The channeled spectra of anisotropic polyethylene terephthalate (PET) transparent films, placed between two identical crossed polarizers were recorded and the linear birefringence was estimated by using the conditions of the minima and maxima of flux density in the channeled spectrum. This method is very fast, allowing the estimation of the linear birefringence over the entire visible range from a single recording of the channeled spectrum. The obtained results are consistent with those previously reported in the literature. [ABSTRACT FROM AUTHOR]

Changes in the birefringence ( Δn NC ) of nanocomposite (NC) gels upon stretching and recovery were investigated for gels comprising a poly( N -isopropylacrylamide)−clay network structure. Irrespective of the composition of the NC gels, a change in the birefringence appeared upon stretching; Δ n NC varied greatly depending on the clay and water contents (C clay and C w , respectively) of the gels and the stretching ratio. The NC gels with low C clay gave rise to unique Δ n NC vs. strain curves with a maximum Δn NC . For samples with higher C clay , the variation of Δn NC s observed in the edge- and through-directions, which is attributed to plane-orientation of the clay platelets, increased with increasing C clay . This was confirmed by scanning electron microscopy observation, and the percentage plane-orientation was evaluated from the Δn NC data. On recovery of the strain, the plane-oriented clay platelets underwent minimal reversion to the original state, although most of the PNIPA chains reverted to the random conformation. The effects of C w on the Δn NC –strain curves were also clarified. [ABSTRACT FROM AUTHOR]

Anisotropy of optical parameters of TaTlS 3 and TaTlSe 3 is investigated through first principles calculations. Indirect bandgap quasi-one-dimensional semiconductors TaTlS 3 and TaTlSe 3 have bandgaps of 1.15 eV and 0.84 eV, respectively. Important optical parameters are found to be strongly influenced by the radiation direction of the incident beam, as indicated by large birefringence and dichroism. Large optical anisotropy suggests promising nonlinear and linear optoelectronic applications for these materials, including wave plates, polarizers and phase-matching devices. • Large optical anisotropy is reported for quasi 1D TaTlX 3 (X = S, Se) materials • The optical properties are investigated through the DFT method using HSE06 functional • TaTlX 3 exhibit large birefringence values in the energy range 1−6 eV • TaTlX 3 exhibit large absorption coefficient in the visible and UV regions • Optical parameters of TaTlX 3 are suitable for optoelectronic applications [ABSTRACT FROM AUTHOR]

Investigation of the optical and electronic properties of the quasi-one-dimensional semiconductor Sb 2 Se 3 is performed with density functional theory, which takes into consideration the spin–orbit coupling and the on-site Coulomb self-interaction. Sb 2 Se 3 has an orthorhombic crystal structure and belongs to the P n m a space group. The pronounced dispersion along the R − U , Z − Γ , Γ − Y , and S − X high-symmetry directions and low dispersion along the U − Z and Y − S directions confirm the layered structure, with strong bonding interactions along the [001] direction, as well as along the [010] direction, along which the SbSe 6 and SbSe 7 chains are aligned, and weak van der Waals interactions along the [100] direction. The material is a semiconductor with an indirect bandgap of 1.2 eV. Sb 2 Se 3 exhibits appreciable carrier mobility and low carrier recombination rates in the plane of the layers, indicating its applicability in solar and photovoltaic devices. Simulated X-ray photoelectron spectra show that the photoelectron emission occurs from the Se p, Sb s, and Se s atomic orbitals, while for high-energy X-rays, photoelectron emission is mainly from Sb s orbital. Sb 2 Se 3 possesses appreciable anisotropy in its refractive index, absorption coefficient, reflectivity, extinction coefficient, and optical conductivity. Sb 2 Se 3 is a negative biaxial crystal, in which the principal optical axis X → a , Y → b , and Z → c. It possesses uniform birefringence in the IR region until the optical cutoff edge at 1030 nm. The material shows strong unidirectional linear dichroism in the wavelength range from 300 nm to 620 nm, with linear dichroism conversion at 275 nm. The energy loss is isotropic for slow electrons below 4.0 eV, but for highly energetic electrons it varies along different crystal directions. Sb 2 Se 3 is a promising material for optoelectronic and polarimetric applications because of its desirable bandgap of 1.2 eV, linear dichroism conversion, and large optical anisotropy, refractive index, dielectric constant, and absorption coefficient. • The anisotropy of quasi-1D Sb 2 Se 3 material is investigated using DFT. • The calculated results are in excellent agreement with the experiments. • Effective mass and hence the mobility show marked anisotropy. • Sb 2 Se 3 exhibits large birefringence and dichroism. • Sb 2 Se 3 is suitable for optoelectronic and photovoltaic applications. [ABSTRACT FROM AUTHOR]

In this manuscript, we report synthesis and physico-chemical characterization of 4-[[4-(butoxy)phenyl]diazenyl]phenyl alkanoates homologous series. For the first time, nineteen derivatives are described here. The enantiotropic nematic phase is typically observed among all members of this series. However, in the case of 4-[[4-(butoxy)phenyl]diazenyl]phenyl stearate, the nematic phase shows a monotropic character. In addition to liquid-crystalline polymorphism, a second crystalline form was observed in some homologs. Furthermore, using a photoelastic modulator, the optical anisotropy in the nematic phase was determined in the first nine compounds of this series. Temperature dependence of optical anisotropy at significantly lower values of reduced temperature is relatively weak. In contrast, optical anisotropy shows a strong temperature effect near isotropization. Moreover, the influence of the ester chain elongation on liquid crystalline and optical properties was established. [ABSTRACT FROM PUBLISHER]