Birefringence Values Research Articles

Two Short-Wave UV Antimony(III) Sulfates Exhibiting Large Birefringence.

In the present work, we have successfully obtained two new UV antimony-based sulfates, NH4Sb(SO4)2 and Ca2Sb2O(SO4)4, by a conventional hydrothermal method. Interestingly, both compounds share similar structural building blocks, such as SbO4 seesaws and SO4 tetrahedra, yet they endow discrepant birefringence values measured at 546 nm with values of 0.150 and 0.114, respectively, owing to the different distortions of the SbO4 groups with SCALP electrons. Moreover, both compounds display large band gaps (4.32 and 4.43 eV, respectively), so they can be used as short-wavelength UV birefringent materials. Moreover, NH4Sb(SO4)2 is a noncentrosymmetric compound, showing a frequency doubling effect of 0.2 × KDP. Detailed structural analyses and calculations confirm the source of superior optical performance and the reasons for the different birefringence of the two compounds. This work provides ideas for the following discovery of antimony-based optical materials with excellent properties.

Exceptional Optical Anisotropy Enhancement Achieved Through Dual-Ions Cosubstitution Strategy in Novel Hybrid Bismuth Halides.

Guided by a superb dual-ions cosubstitution strategy, two novel, highly optically anisotropic hybrid bismuth halides are designed and synthesized. The first compound, Gu3Bi2NO3Cl8 (Gu = C(NH2)3), is developed using the 2D perovskite halide Cs3Bi2Cl9 as the maternal structure. This involved substituting all Cs+ cations with organic Gu+ and replacing some Cl- anions with [NO3]-. Further substitution of Cl- with additional [NO3]- resulted in the formation of nitrate-rich Gu2Bi(NO3)3Cl2 crystal, exhibiting a 3.4-fold increase in [NO3]- per unit volume. Both compounds have a structurally 0D nature, comprising bismuth-centered polyhedra formed by coordinated chlorides and monodentate/bidentate nitrate moieties, with Gu+ serving as a separator and linker. Notably, the presence of superb optically anisotropic dual-ions, i.e., planar Gu+ and [NO3]-, enables these crystals to possess sharply enhanced optical anisotropy, with birefringence values more than 1 order of magnitude higher than that of the initial crystal Cs3Bi2Cl9 (0.162/0.186vs 0.011 at 546nm). The discovery and characterization of Gu3Bi2NO3Cl8 and Gu2Bi(NO3)3Cl2 crystals provide new insights into achieving expected modifications in optical properties through the utilization of a dual-ions cosubstitution strategy.

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.

Nematic liquid crystal dispersed with two-dimensional functionalised graphene oxide (fGO): insights on improving the nematic ordering and reducing electro-optic response time

ABSTRACT Doping a nematic liquid crystal (NLC) with nanoparticles (NPs) of varied dimensions and properties to form LC-NP nanocomposites with improved electro-optic and dielectric properties has recently been a much-explored field of work. But still, NLC nanocomposites based on two-dimensional (2D) NPs have not been studied vividly because of the high tendency of 2D NPs to aggregate together. In the present work, we have studied the effect of incorporating hexadecanethiol functionalised graphene oxide (fGO), a 2D NP, in a conventional NLC medium under varying doping concentrations. We found that at a lower doping concentration (⁓10−4 wt.%), the NLC nanocomposite showed a substantial increase in dielectric anisotropy (Δε) and birefringence (Δµ) values as compared to pure NLC sample. A significant decrease (⁓50%) in ionic conductivity as well as reduced electro-optic response time (⁓75%) was also observed in this NLC nanocomposite. As the fGO doping concentration was increased (⁓10−2 wt.%), a reverse trend was observed for Δε, Δµ and response time values, which declined sharply with increasing doping concentration. Hence, the present work highlights two different working mechanisms at low- and high-doping concentrations of 2D NPs.

Reconstructing nearly isotropic microstructures to construct a one-dimensional framework causing record birefringence in thiophosphates.

Infrared birefringent crystals that hold significant importance for optoelectronic application have been rarely reported. Traditional tetrahedral PS4, ethane-like P2S6, and octahedral InS6 units in thiophosphates typically manifest near isotropy, often resulting in extremely small birefringence. However, this study prepares α-Rb2InP2S7 (1), β-Rb2InP2S7 (2), and Cs2InP2S7 (3), consisting of the aforementioned microstructures, notably exhibiting the highest refractive index difference or birefringence values (0.247, 0.298, and 0.250 at 546 nm, respectively) among thiophosphates, the middle one being larger than that of commercial birefringent materials. This unusual increase in birefringence can be primarily attributed to two key factors: (1) simultaneous stretching and compressing of the P-S and In-S covalent bond interactions, generating high polarizability anisotropy of InS6, PS4, and P2S6 polyhedral units; (2) the additional incorporation of alkali metals that further reduces the dimensionality of the crystal structure, creating one-dimensional [InP2S7]2- structures with increasing polarizability anisotropy. This study presents an alternative approach to enhance birefringent materials by reconstructing covalent bond interactions and specific spatial arrangements.

Photoinduced birefringence in azopolymers measured at 1550 nm

Azobenzenes are a class of compounds presenting photoisomerization capabilities that allow the writing and erasure of birefringence along a desired direction. This feature enables applications requiring polarization control, which although have been extensively investigated in the visible light spectrum, poor emphasis has been paid to the infrared region. In this paper, a systematic characterization of induced birefringence creation and relaxation dynamics has been carried out in azopolymers thin films in the infrared telecommunications region of 1550 nm. This study covers both birefringence characterization in terms of wavelength and irradiance of birefringence writing beams. Preliminary results revealed remarkable maximum birefringence values as high as 0.0465 attained during the recording phase, that stabilized at 0.0424 during the relaxation phase, which is quite promising for many applications.

Crystal clear: unveiling giant birefringence in organic-inorganic cocrystals.

Coplanar groups with large anisotropic polarizability are suitable as birefringence-active groups for investigating compounds with significant birefringence. In this study, the organic coplanar raw reagent, o-C5H5NO (4HP), was selected as an individual complement. Utilizing the cocrystal engineering strategy, we successfully designed two cocrystals: [LiNO3·H2O·4HP]·4HP (Li-4HP2) and [Mg(NO3)2·6H2O]·(4HP)2 (Mg-4HP), and one by-product: LiNO3·H2O·4HP (Li-4HP), which were grown using a mild aqua-solution method. The synergy of the coplanar groups of NO3 - and 4HP in the structures resulted in unexpectedly large birefringence values of 0.376-0.522@546 nm. Furthermore, the compounds exhibit large bandgaps (4.08-4.51 eV), short UV cutoff edges (275-278 nm), and favorable growth habits, suggesting their potential as short-wave UV birefringent materials.

Extended centroid position method in liquid-crystal-based interrogation system for electric-field-modulated Fabry-Perot sensing

A polarized low-coherence interferometer (PLCI) based on a liquid crystal (LC) wedge is designed, and an associated demodulation method encompassing the tunability feature is proposed for tunable, standalone optical sensing. The application of an electric field to the LC material effectively decreases the birefringence value and the related dispersion relation, which in turn enhances the resolution of detection. The effect of the electric field on the demodulation of the cavity length is addressed by the successive determinations of the centroid positions of the PLCI interferograms. Through a comprehensive study of numerical simulations, the effectiveness of the proposed approach is explored relative to the conventional envelope detection methodology. In order to verify this method, an experiment with a Fabry-Perot-based fiber optic displacement sensor is carried out using a 5CB LC wedge-based PLCI setup in the presence of an electric field. The measurement accuracy of the cavity length is found to be 0.74% of full scale, rendering it more precise and robust than the conventional envelope detection method.

DIAGNOSTICS OF GENITAL ENDOMETRIOSIS USING METHODS OF POLYCRYSTALLINE STRUCTURE POLARIZATION-PHASE INTROSCOPY

This article contains the following results of research the diagnosis of genital endometriosis of uterine preparations by the methods of polarization- phase Muller- matrix introscopy.The aim of the study. To estimate the eff ectiveness of diff erential diagnosis of genital endometriosis using polarization- phase Muller- matrix introscopy of histological sections of endometrial biopsy.Material and methods. Two groups of samples were studied:● biopsy of «healthy» uterine tissue obtained during diagnostic hysteroscopy – «control group 1.1» – 68 samples;● biopsy of uterine tissue with genital endometriosis – «experimental group 1.2» – 59 samples.Histological sections were made according to the standard technique on a microtome with rapid freezing. Research results. The analysis of the obtained statistical analysis data revealed the adequacy of the prognostic variant of changes in the polycrystalline structure of histological sections of endometrial biopsy. For patients with genital endometriosis, there is a signifi cant increase in linear birefringence.Diagnostic markers of this pathological process are an increase in the average value and dispersion of linear birefringence. The values of asymmetry and kurtosis, on the contrary, decrease.Statistical confi rmation of this is a statistically signifi cant diff erence (pi=1;2;3;4<0.05) between the values of the set of all central statistical moments of the 1st-4th orders, characterize the distributions of the PLD value of histological sections of endometrial biopsy for cases of conditional norm (control group 1.1) and genital endometriosis (experimental group 1.2).Conclusions. Therefore, the conducted set of studies using polarization- phase Muller- matrix introscopy of histological sections of endometrial biopsy revealed a high (up to 100 %) eff ectiveness of diff erential diagnosis of genital endometriosis. Therefore, it is relevant to study the diagnostic capabilities of this technique for more easily accessible objects – biological fl uids.

Designing Sulfate Crystals with Strong Optical Anisotropy through π‐Conjugated Tailoring

AbstractSulfate 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.

Designing Sulfate Crystals with Strong Optical Anisotropy through π-Conjugated Tailoring.

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-C5 H4 NSO3 ) ⋅ xH2 O (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.

Synthesis and characterization of low retardation colorless polyimides containing m-phenylenediamine with different pendant groups

In this study, 4-biphenyl-3,5-diaminobenzoate (E- m-PDA) was synthesized by three steps using 3,5-dinitrobenzoic acid as a starting material. Two series of colorless polyimides (CPIs) PI-(1a-1d) and PI-(2a-2d) were prepared by traditional two-step polycondensation of m-phenylenediamine ( m-PDA) based diamines with different pendant groups (-H, CF3, COOH and biphenyl ester) with aromatic dianhydrides BPADA and 6FDA, respectively. All of the prepared CPIs exhibited high thermal stability with 5% weight loss at temperatures ranging from 428 to 539°C in nitrogen, and glass transition temperatures ( Tgs) ranging from 228 to 332°C. These PI films displayed a UV-vis absorption cut-off wavelength at 338–376 nm and transparency of 76%–89% at a wavelength of 450 nm. Both series of colorless PI films also showed low birefringence values of 0.0021–0.0100. In addition, the optical retardations of these CPIs were extremely low (48–220 nm), indicating low optical anisotropy of these CPI films. Colorless PI film PI-2d prepared based on E- m-PDA and 6FDA had good comprehensive properties of low birefringence ([Formula: see text] n of 0.0064), high Tg (319°C) and excellent transparency ( T450 of 88%).

On the low-temperature isotropic point in Rb2SO4 crystals

In this work, Rb2SO4 single crystals of good optical quality were synthesized and the spectral (300–700 nm) and temperature (300–77 K) dependencies of birefringence were experimentally investigated. It was found that with a temperature decreasing, at a temperature of T = 85 K and a light wavelength of λ = 500 nm, the birefringence value in the Y direction is zero (Δny = nz – nх = 0), which testifies to the existence of a new isotropic point. The influence of uniaxial compression on changes in Δny (Т, λ) was studied, and their significant sensitivity was revealed. The temperature-baric and spectral-baric changes of the isotropic point position were analyzed, based on which the temperature-spectral-baric diagram of the isotropic state of the crystal was constructed, which will be of practical importance for the use of crystal as an active element in a crystal-optical temperature sensor for a low-temperature region. Based on the Δny (Т, λ, σ) dependencies, the combined piezo-optic coefficients of the crystal were estimated, and it was assumed that not only thermal but also mechanical deformation of the optical indicatrix takes place in the vicinity of the isotropic point.

Synthesis and characterization of semi‐alicyclic transparent polyimide films containing benzanilide and fluorene units with improved high‐temperature dimensional stability and low‐optical retardations

AbstractTwo solution‐processable semi‐alicyclic transparent polyimide (PI) films with improved high‐temperature dimensional stability and low‐optical retardations were prepared from the stereo‐isomeric alicyclic dianhydrides, 1S,2R,4S,5R‐hydrogenated pyromellitic dianhydride (ccHPMDA) and 1R,2S,4S,5R‐hydrogenated pyromellitic dianhydride (ctHPMDA) and an aromatic diamine, 9,9‐bis[4‐(4‐aminobenzamide)phenyl]fluorene (FDAADA), respectively. The alicyclic cyclohexane units in the dianhydride moiety endowed the derived PI‐1 (ccHPMDA‐FDAADA) and PI‐2 (ctHPMDA‐FDAADA) films good optical transparency, the rigid‐rod benzanilide units provided the PI films low coefficients of thermal expansion (CTE), and the fluorene units resulted in good solution processability and low‐optical retardations (Rth) for the PI films. The PI films exhibited the glass transition temperatures over 400°C and the CTE value of 33.2 × 10−6/K for PI‐1 and 29.0 × 10−6/K for PI‐2 in the temperature range of 50 ~ 250°C, respectively. In addition, the PI films showed good optical transparency in the ultraviolet–visible light region with the optical transmittances higher than 80% for PI‐1 film at the wavelength of 500 nm. The PI films exhibited the average refractive indices of 1.6505 for PI‐1 and 1.6485 for PI‐2 film, respectively. The birefringence values of the PI films were all lower than 0.01, resulting in the low‐optical anisotropies with the optical retardation (Rth) of 77 nm for PI‐1 film and 84 nm for PI‐2 film.

A first principles characterization of electronic and optical anisotropy of quasi-one-dimensional transition metal lead sulfides PbMS3 (M [formula omitted] Hf, Zr)

PbMS3 (M = Hf, Zr) are ternary sulfides with the general structure ABX3, 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 PbMS3, and their applicability in optoelectronic devices using first principles DFT calculations. PbHfS3 is an indirect bandgap semiconductor (1.2 eV), whereas PbZrS3 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.

Characterization of Chiral Nanostructured Surfaces Made via Colloidal Lithography.

Optically anisotropic materials were produced via colloidal lithography and characterized using scanning electronic microscopy (SEM), confocal microscopy, and polarimetry. A compact hexagonal array mask composed of silica sub-micron particles was fabricated via the Langmuir-Blodgett self-assembly technique. Subsequently, the mask pattern was transferred onto monocrystalline silicon and commercial glass substrates using ion beam etching in a vacuum. Varying the azimuthal angle while etching at oblique incidence carved screw-like shaped pillars into the substrates, resulting in heterochiral structures depending on the azimuthal angle direction. To enhance the material's optical properties through plasmon resonance, gold films were deposited onto the pillars. Polarimetric measurements were realized at normal and oblique incidences, showing that the etching directions have a clear influence on the value of the linear birefringence and linear dichroism. The polarimetric properties, especially the chiroptical responses, increased with the increase in the angle of incidence.

Topas‐based octa‐circular cladding and rectangular porous core photonic crystal fibre for terahertz waveguide

AbstractThis article presents a novel design for guiding terahertz (THz) waves, which utilises a photonic crystal fibre with a porous core (PC‐PCF). This approach is substantiated by a Topas‐based octagonal‐shaped core with rectangular air slots. By utilising Finite Element Method and Perfectly Matched Layer boundary condition, the guiding properties of a structure consisting of octagonal air holes integrated with circular air slots in the cladding region have been investigated. The proposed structure exhibits a birefringence value of 0.05 and a low effective material loss of 0.013 cm−1. Moreover, it exhibits flattened dispersion measuring at a wide‐ranging frequency of 0.4 to 1.6 THz. In addition to that, the proposed structure offers 60% high core power fraction, 10−18 cm−1 confinement loss at 65% porosity of 290 μm core diameter and 1.6 THz frequency. Other significant waveguide properties: effective refractive index, effective area, spot size, and beam divergence of the proposed fibre are numerically analysed and discussed rigorously along with the fabrication viability of the fibre with existing techniques.

Cross-correlation power spectra and cosmic birefringence of the CMB via photon-neutrino interaction

In the context of the standard model of particles, the weak interaction of cosmic microwave background (CMB) and cosmic neutrino background (CνB), can generate non-vanishing TB and EB power spectra in the order of one loop forward scattering, in the presence of scalar perturbation, which is in contrast with the standard scenario cosmology. Comparing our results with the current experimental data may provide, significant information about the nature of CνB, including CMB-CνB forward scattering for TB, TE, and EB power spectra. To this end, different cases were studied, including Majorana CνB and Dirac CνB. On the other hand, it was shown that the mean opacity due to cosmic neutrino background could behave as an anisotropic birefringent medium and change the linear polarization rotation angle. Considering the contributions from neutrino and anti-neutrino forward scattering with CMB photons (in the case of Dirac neutrino), we introduce relative neutrino and anti-neutrino density asymmetry (δν = Δnν /nν = nν -nν̅ /nν ). Then, using the cosmic birefringence angle reported by the Planck data release β = 0.30° ± 0.11° (68%C.L.), some constraints can be put on δν . Also, the value of cosmic birefringence due to Majorana CνB medium is estimated at about β| ν ≃ 0.2 rad. In this respect, since Majorana neutrino and anti-neutrino are exactly the same, both CB contributions will be added together. However, this value is at least two orders larger than the cosmic birefringence angle reported by the Planck data release, β = 0.30° ± 0.11° (68%C.L.). Finally, we shortly discussed this big inconsistency. It is noteworthy that to calculate the contribution of photon-neutrino forward scattering for cosmic birefringence, we just consider the standard model of particles and the standard scenario of cosmology.

The influence of degradation in different pH buffer solutions on the optical and durability properties of Monocryl suture: (an in vitro study)

The objective of this work is to investigate the hydrolytic degradation of the Monocryl (PGA/PCL) surgical suture in different pH buffer solutions, and its correlation with the structural alterations the material undergoes. To this end, an in vitro degradation study was conducted under acidic (pH = 2), physiological (pH = 7.4), and alkaline (pH = 8.5) conditions at 37 °C, over 25 days. Changes in the swelling rate, structural and mechanical properties of the Monocryl sample with the degradation time were characterized, from which the related degradation mechanism of the material was concluded. Results showed that the structural values of the Monocryl sample were more sensitive in the alkaline medium than the acidic and neutral ones. It exhibited a reduction in birefringence values by 11.5% from the original one in the buffer solution of pH = 8.5, only 4% at pH = 2, and 2.6% at pH = 7.4, after 20 days of degradation durations. Over the same time period, mechanical loss in neutral, acidic, and alkaline media was decreased to 19, 14.9, and 8.3%, respectively. The obtained results revealed that the Monocryl suture exhibits enhanced degradation properties in neutral conditions rather than both acidic and alkaline ones, with a more homogeneous degradation behavior during the degradation process.Graphical abstract

AAl(Te4O10) (A = Na, Ag) and K2Ga2(HTe6O16)(HTeO3): Three Aluminum/Gallium Tellurites with Large Birefringence and Wide Band Gap

The exploration of novel inorganic tellurites is significant because of their promising applications in nonlinear-optical materials and birefringent materials. Herein, three new aluminum/gallium tellurites, namely, NaAl(Te4O10) (1), AgAl(Te4O10) (2), and K2Ga2(HTe6O16)(HTeO3) (3), have been successfully obtained by mild hydrothermal reactions. The isostructural compounds 1 and 2 contain the Te3O8 trimer, while compound 3 contains an unprecedented Te6O16 hexamer. Notably, all three compounds exhibit large birefringence values of over 0.1 at 532 nm, which are currently the largest reported birefringence values among tellurium(IV) oxides without additional anionic groups.