Birefringence Research Articles

Determining the Optical Geometry of a Gold Semi-Shell under the Kretschmann Configuration

Dielectric nanoparticles coated with metals (half-shell or semi-shell structures) have attracted attention as potential composite plasmonic nanomaterials with large optical anisotropy and absorption cross-sections. Structures approximately 100 nm in size can excite plasmons in the visible and near-infrared ranges, highlighting their distinct optical properties. This study employed metal semi-shell structures (metal: gold, dielectric: silica) in the Kretschmann configuration to experimentally and numerically demonstrate the optical determination of single-structure orientations through a finite-difference time-domain method. Gold semi-shell structures were fabricated through deposition and etching. These structures were removed from their substrate in ultrapure water and randomly dropped onto a thin gold substrate. In the single structure, we experimentally observed changes in the scattering light spectrum based on the optical geometry of the gold semi-shell at wavelengths ranging from 530 to 700 nm. The obtained results closely resembled those of a simulation and confirmed the presence of eigenmodes in the orientation through electric field analysis. These observations allow for the cost-effective and rapid determination of the orientations of numerous structures that are approximately 100 nm in size, solely through optical methods. This technique is a valuable development for measurement applications in nanostructure orientation control and functionality enhancement.

Variation of Ionospheric Shortwave Absorption of the Extraordinary Wave

AbstractIn this study, associating with the A‐H formulation, we have developed a comprehensive ionospheric absorption model by incorporating the latest version of geomagnetic model, the atmospheric and ionospheric model as the background. Based on the absorption model, the ionospheric stratification theory is utilized to explore the trend of the total absorption for extraordinary (X) wave with frequency and elevation angle. We found that the factor of local time has a greater impact on the trend of total absorption variation than other factors—solar activity, season, and latitude, attributing to the variation of electron collision frequency. During the two different local times (daytime and night), the trends of the total absorption have distinct differences. In the daytime, it is worth noting that the reflection heights and the peaks of the absorption coefficient both mainly occur in Layers D and E. Therefore, the non‐deviative absorption dominates the variation of the total absorption. On the other hand, the occurrence of Pedersen ray results in inflexion points arising in the curves of absorption versus frequency or elevation angle. Another interesting phenomenon is the dominant role of deviative absorption at night. At night, the reflection heights mainly occur in Layer F, and the absorption coefficient of Layer F begins to exceed the peak levels of Layers D and E when the frequency or elevation angle is larger than certain values. Hence, the total absorption will grow as a result of the increase in deviative absorption with the increase in reflection height and absorption coefficient.

Optical and electrical anisotropies in Cu2ZnSnS4 and Cu2MgSnS4 thin films deposited by thermal evaporation at obliquely incident angle

Optical and electrical anisotropies in Cu2ZnSnS4 and Cu2MgSnS4 thin films deposited by thermal evaporation at obliquely incident angle

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 matching a microwave radiation with the plasma of an electron cyclotron resonance discharge

This article proposes a scheme for matching microwave radiation with a magnetized plasma of an electron cyclotron resonance (ECR) discharge in an open magnetic trap, using the effect of depolarization—the transformation of the ordinary wave into the extraordinary one upon reflection from the metal walls of a plasma chamber. An analysis of the efficiency of such a transformation is carried out, and it is shown that for grazing (less than 15° with metal surface) angles of incidence; it is possible to achieve an efficiency exceeding 90%.

An Integrated Photoelasticity-Based Approach for the Reconstruction of Stress Profiles and Optical Anisotropy of GRIN Lenses

The paper shows that it is possible to obtain reliable information on the dependence of the radial distribution of longitudinal birefringence in glass cylindrical elements with a radial distribution of refractive index (GRIN lenses) on the basis of transverse polarization tomography data on residual stresses. This does not require complicated procedures of sample preparation, as is necessary in the case of longitudinal translucency measurements. The approach developed was verified in the experiments with a set of different GRIN lenses formed with the ion exchange technique, and the closeness of the data obtained from transversal and conventional longitudinal transmission measurements was demonstrated.

An extraordinary wave of SARS-CoV2, the youngest and the least serious.

The second wave of SARS-CoV2 in our health region began at the end of June 2020 coinciding with the widespread decrease in cases in all areas of Catalonia. This resulted in the relaxation of measures that coincided with the end of the school year and the arrival of seasonal workers for the fruit-picking campaign. This led to a rapid increase in cases that culminated in perimeter confinement of the Segrià in July 2020, the only such measure imposed in the whole of Spain that month. This increase in cases was attributed to the influx of agricultural workers with a change of trend in the age of persons affected that had until then consisted mainly of older people. Simultaneously, in other areas of Catalonia the number of cases had dropped dramatically.

Renal Amyloidosis: A Narrative Literature Review

Amyloidosis is a disorder in which soluble proteins aggregate and are deposited extracellularly in tissues as insoluble fibrils, causing progressive organ dysfunction. Amyloid fibril formation begins with misfolding of amyloidogenic precursor proteins. The fibrils have a characteristic appearance by electron microscopy and produce double refraction under polarized light when stained with Congo red dye. Classification of amyloidosis is based on the precursor proteins that form amyloid fibrils and the distribution of amyloid deposition both systemically and locally. The main form of systemic amyloidosis; AL amyloid, AA amyloidosis, ATTR amyloid. The kidney is the organ most frequently involved in systemic amyloidosis. Systemic amyloidosis may originate from anomalous proteins, such as immunoglobulin light chains or serum amyloid protein in chronic inflammation or may arise from hereditary disorders. The clinical manifestations of renal amyloidosis vary with the type of amyloid protein and the location and extent of amyloid deposition. Treatment of amyloidosis should be a two-part process; managing symptoms and reducing or stabilizing amyloid protein. Treatment of amyloidosis is focused on reducing the production of amyloidogenic proteins and inhibiting their aggregation.

Controllable Growth of Large-Scale Continuous ReS2 Atomic Layers

In recent years, two-dimensional (2D) layered transition metal dichalcogenides (TMDs) have received significant attention due to their exceptional electrical and optical properties. Among these 2D materials, ReS2 distinguishes itself through its unique optical and conductance anisotropy. Despite concerted efforts to produce high-quality ReS2, the unique interlayer decoupling properties pose substantial challenges in growing large-area ReS2 thin films, with the preparation of single layers proving even more complex. In this work, large-scale continuous monolayer and bilayer ReS2 films were successfully grown on mica substrates using low-pressure chemical vapor deposition (LPCVD). Photodetectors were fabricated using the prepared high-quality ReS2 films, and the devices presented stable photoresponse and enhanced response sensitivity. The production of continuous ReS2 atomic layers heralds promising prospects for large-scale integrated circuits and advances the practical application of optoelectronics based on 2D layered materials.

Flexible Anionic Groups-Activated Structure Dissymmetry for Strong Nonlinearity in Ln2 Ae3 MIV 3 S12 Family.

Structural dissymmetry and strong second-harmonic generation (SHG) responses are key conditions for nonlinear optical (NLO) crystals, and targeted combinatorial screening of suitable anionic groups has become extremely effective. Herein, optimal combination of flexible SnSn (n=5, 6) groups and highly electropositive cations (lanthanides (Ln3+ ) and alkaline earth (Ae2+ : Sr, Ca) metals) affords the successful synthesis of 12 NLO thiostannates including Ln2 Sr3 Sn3 S12 (Pmc21 ) and Ln2 Ca3 Sn3 S12 (P-62m); whereas 17 rigid GeS4 or SiS4 tetrahedra-constructed Ln2 Ae3 Ge3 S12 and Ln2 Ae3 Si3 S12 crystallize in the centrosymmetric (CS) Pnma. This unprecedented CS to noncentrosymmetric (NCS) structural transformation (Pnma to P-62m to Pmc21 ) in the Ln2 Ae3 MIV 3 S12 family indicates that chemical substitution of the tetrahedral GeS4 /SiS4 units with SnSn breaks the original symmetry to form the requisite NCS structures. Remarkably, strong polarization anisotropy and hyperpolarizability of the Sn(4+) S5 unit afford huge performance improvement from the nonphase-matching (NPM) SHG response (1.4×AgGaS2 and Δn=0.008) of La2 Ca3 Sn3 S12 to the strong phase-matching (PM) SHG effect (3.0×AgGaS2 and Δn=0.086) of La2 Sr3 Sn3 S12 . Therefore, Sn(4+) S5 is proven to be a promising "NLO-active unit." This study verifies that the coupling of flexible SnSn building blocks into structures opens a feasible path for designing targeted NCS crystals with strong nonlinearity and optical anisotropy.

Structure and anisotropic optical properties of γ-InSe under high pressure

Pressure is believed to be one effective method to modify the structure and properties of 2D materials. In the present work, the structural transition and anisotropic properties of γ-InSe were in situ investigated under pressure using Raman, photoluminescence and infrared spectra, as well as the density functional theory. Results reveal that γ-InSe would transform to one metallic phase of InSe-III above 11.4 GPa. Below this transition pressure, γ-InSe completely transforms to the high temperature high pressure phase of InSe-II after three pressure up-down cycles. This is the first report on InSe-II obtained at ambient temperature. Besides phase transitions, one direct-to-indirect band transition is observed around 4 GPa. Angle-resolved polarized Raman spectra show all its three phonon modes exhibit 90° periodic variations, yielding a 4-fold symmetry. Pressure would not change its 4-fold symmetry, but its polarized angles vary with pressure. Therefore, pressure has important effect on γ-InSe that induces its structure change and thus results in its optical anisotropy variation.

Designing a Hybrid Perovskite with Enlarged Birefringence and Bandgap for Modulation of Light Polarization.

Birefringent crystals have important applications in optoelectronics areas due to their ability to modulate and polarize light. Despite increasing discovery of the birefringence potential of new crystals, it remains a great challenge to optimize both birefringence and bandgap simultaneously. Herein, a 1D chain-like hybrid perovskite birefringent crystal designed by 3D-to-1D dimensional tailoring, (GAM)2 PbI7 ·H2 O (GAM=C5 N10 H10 ), is presented, showing enlarged birefringence of 0.49@550nm and enlarged optical bandgap (2.48eV). Consequently, the birefringent quality factor of (GAM)2 PbI7 ·H2 O is up to 2.8 times that of the template MAPbI3 . In particular, the birefringence is much larger than those of commercial birefringent crystals and surpasses that of the vast majority of hybrid perovskite known to date. Theoretical calculations reveal that the strongly anisotropic arrangement of (GAM)2.5+ π-conjugated cations and ordered PbI6 octahedra contributes to the large birefringence and wide bandgap of (GAM)2 PbI7 ·H2 O. It is believed that this work will provide a new pathway toward the rational design and synthesis of hybrid perovskite birefringent crystals for compact wide-bandgap polarization dependent devices.

Ab-initio investigation of the physical properties of BaAgAs Dirac semimetal and its possible thermo-mechanical and optoelectronic applications

BaAgAs is a ternary Dirac semimetal which can be tuned across a number of topological orders. In this study we have investigated the bulk physical properties of BaAgAs using density functional theory based computations. Most of the results presented in this work are novel. The optimized structural parameters are in good agreement with previous results. The elastic constants indicate that BaAgAs is mechanically stable and brittle in nature. The compound is moderately hard and possesses fair degree of machinability. There is significant mechanical/elastic anisotropy in BaAgAs. The Debye temperature of the compound is medium and the phonon thermal conductivity and melting temperature are moderate as well. The bonding character is mixed with notable covalent contribution. The electronic band structure calculations reveal clear semimetallic behavior with a Dirac node at the Fermi level. BaAgAs has a small ellipsoidal Fermi surface centered at the Γ-point of the Brillouin zone. The phonon dispersion curves show dynamical stability. There is a clear phonon band gap between the acoustic and the optical branches. The energy dependent optical constants conform to the band structure calculations. The compound is an efficient absorber of the ultraviolet light and has potential to be used as an anti-reflection coating. Optical anisotropy of BaAgAs is moderate. The computed repulsive Coulomb pseudopotential is low indicating that the electronic correlations in this compound are not strong.

A potassium lead 2-methylmalonate-iodide nonlinear optical crystal with strong second-harmonic generation response and large birefringence

Nonlinear optical (NLO) crystals play a significant role in optoelectronic industry. Herein, a new NLO crystal, K(H2O)[KI][PbI(C4H4O4)], has been rationally obtained by tuning halide perovskite materials with 2-methylmalonate group. K(H2O)[KI][PbI(C4H4O4)] features that the highly distorted [PbO4I2] polyhedron with large hyperpolarizability and prominent polarizability anisotropy is served as a bifuntional unit. Remarkably, the distorted [PbO4I2] polyhedrons are aligned in an oriented arrangement that leads to the effective superposition of their microscopic second-order nonlinear susceptibilities and the enhancement of optical anisotropy. Notably, K(H2O)[KI][PbI(C4H4O4)] exhibits a strong phase-matching SHG response of 5.6 × KDP and a large birefringence (Δnobv. = 0.24@546 nm). Theoretical calculations elucidate that the strong SHG response and the large birefringence are predominantly attributed to the directional arrangement of the highly distorted [PbO4I2] polyhedrons. Our discovery provides an effective path for the rational exploration of high-performance NLO crystals.

A Two-Dimensional Hybrid Perovskite With Heat Switching Birefringence.

Birefringent crystals that can switch light polarization have important applications in optoelectronics. In the last decades, birefringence is mostly optimizedby 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.

A Two‐Dimensional Hybrid Perovskite With Heat Switching Birefringence

AbstractBirefringent 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.

Narrow intensity range optical anisotropy in air induced by a femtosecond laser breakdown.

In this paper, we study the optical anisotropy induced by femtosecond laser radiation in air during an optical breakdown. Using a transverse pump-probe technique, we demonstrate that this anisotropy appears in a narrow range of pump intensities, which are close to the optical breakdown threshold in air and lead to a phase shift of probe radiation, polarized collinear to the pump. The intensity range where an induced intense anisotropy occurs makes it possible to estimate the magnitude of the 5th-order Kerr nonlinear refractive index component in air.

YSO4F·H2O: A Deep-Ultraviolet Birefringent Rare-Earth Sulfate Fluoride with Enhanced Birefringence Induced by Fluorinated Y-Centered Polyhedra.

Birefringent crystals can modulate and detect the polarization of light and are important optical functional materials. The birefringence is positively correlated to the anisotropy of the structure. By partially substituting sulfate anion with large electronegative fluorine in the parent compound Y2(SO4)3·8H2O, a new fluorinated rare-earth sulfate YSO4F·H2O with enhanced anisotropy was achieved. YSO4F·H2O features a dense 3D structure constructed by the polarizable [YOF] polyhedra and [SO4] tetrahedra. The diffuse reflectance spectrum reveals that it has a short UV absorption edge of below 200 nm. The substitution of the F- ion enhances the optical anisotropy, making the material exhibit an enhanced birefringence (0.0357 at 546 nm), which is 5.1 times that of the parent compound and is also larger than most deep-UV birefringent sulfates. It is expected that this work may shed useful insights in the exploration of deep-UV birefringent materials with enhanced optical performances..

Highly Anisotropic Mechanical Response of the Van der Waals Magnet CrPS4

AbstractSemiconducting van der Waals magnets exhibit a rich physical phenomenology with different collective excitations, as magnons or excitons, that can be coupled, thereby offering new opportunities for optoelectronic, spintronic, and magnonic devices. In contrast with the well‐studied van der Waals magnets CrI3 or Fe3GeTe2, CrPS4 is a layered metamagnet with a high optical and magnon transport anisotropy. Here, the structural anisotropy of CrPS4 above and below the magnetic phase transition is investigated by fabricating nanomechanical resonators. A large anisotropy is observed in the resonance frequency of resonators oriented along the crystalline a‐ and b‐axis, indicative of a lattice expansion along the b‐axis, boosted at the magnetic phase transition, and a rather small continuous contraction along the a‐axis. This behavior in the mechanical response differs from that previously reported in van der Waals magnets, as FePS3 or CoPS3, and can be understood from the quasi‐1D nature of CrPS4. The results pinpoint CrPS4 as a promising material in the field of low‐dimensional magnetism and show the potential of mechanical resonators for unraveling the in‐plane structural anisotropy coupled to the magnetic ordering that, in a broader context, can be extended to studying structural modifications in other 2D materials and van der Waals heterostructures.

Optical anisotropy and refractive index dispersion of Zn2GeO4 microrods

Dielectric resonators with high light confinement offer low optical losses, which is essential for the development of high-performance optoelectronic devices. Among the different compounds, Zn2GeO4 has emerged as a promising wide band gap transparent conductive oxide with a low-dielectric constant. In order to control and optimize their optoelectronic properties, a good knowledge of their optical constants, such as the refractive index, is required. Here, we exploit the behaviour of Zn2GeO4 microrods as optical cavities to estimate experimentally for the first time, so far as we know, the refractive index dispersion of this compound. In addition, first principle calculations by density functional theory (DFT) of the dielectric function as a function of the light propagation direction have been performed, which have revealed a strong optical anisotropy. The results show that there is also an influence of native defects on the optical propagation properties. These physical aspects are crucial to tailor the optical features of Zn2GeO4 and exploit them in optoelectronic devices with bespoke properties.