Linear Anisotropy Research Articles

Elliptic Hermite-Gaussian soliton and transformations in nonlocal media induced by linear anisotropy.

Elliptic Hermite-Gaussian (HG) soliton clusters in nonlocal media with anisotropic diffractions are studied comprehensively. The relations among solitons parameters, diffraction indices, and the degree of nonlocality are derived analytically with the Lagrangian method. Stable elliptic HG soliton clusters can be obtained when linear diffraction is anisotropic. When the solitons are launched with an initial orientation angle, we also demonstrate numerically mode transformations between HG and Laguerre-Gaussian (LG) solitons induced by linear anisotropy. Our results will enrich the soliton phenomenon with linear anisotropic diffraction and may lead to novel applications in all-optical switching, interconnection, etc.

Asymmetric center manipulation allows luminescent materials with room temperature phosphorescence and polarized emission

A chemical method to obtain purely organic materials with room temperature phosphorescence and tuned polarized emission is developed. The chirality of the asymmetry center can be precisely controlled bottom-up exhibiting either a reserved or inverted configuration, without enantiomer separation procedures. Developed luminescent materials with varied chiral configurations show polarized photoluminescence and room temperature phosphorescence up to seconds, which can be used for time- and polarization dependent microscopy applications, with an integrated linear polarization anisotropy factor as large as 0.44.

Strongly Bound Excitons and Anisotropic Linear Absorption in Monolayer Graphullerene.

Graphullerene is a novel two-dimensional carbon allotrope with unique optoelectronic properties. Despite significant experimental characterization and prior density functional theory calculations, unanswered questions remain as to the nature, energy, and intensity of the electronic and optical excitations. Here, we present first-principles calculations of the quasiparticle band structure, neutral excitations, and absorption spectra of monolayer graphullerene and bulk graphullerite, employing the GW-Bethe-Salpeter equation (GW-BSE) approach. We show that strongly bound excitons dominate the absorption spectrum of monolayer graphullerene with binding energies up to 0.8 eV, while graphullerite exhibits less pronounced excitonic effects. Our calculations also reveal a strong linear polarization anisotropy, reflecting the in-plane structural anisotropy from intermolecular coupling between neighboring C60 units. We further show that the presence of Mg atoms, crucial to the synthesis process, induces structural modifications and polarizability effects, resulting in a ∼1 eV quasiparticle gap renormalization and a reduction in the exciton binding energy to ∼0.6 eV.

Numerical evaluation of spinal reconstruction using a 3D printed vertebral body replacement implant: effects of material anisotropy.

Artificial vertebral implants have been widely used for functional reconstruction of vertebral defects caused by tumors or trauma. However, the evaluation of their biomechanical properties often neglects the influence of material anisotropy derived from the host bone and implant's microstructures. Hence, this study aims to investigate the effect of material anisotropy on the safety and stability of vertebral reconstruction. Two finite element models were developed to reflect the difference of material properties between linear elastic isotropy and nonlinear anisotropy. Their biomechanical evaluation was carried out under different load conditions including flexion, extension, lateral bending and axial rotation. These performances of two models with respect to safety and stability were analyzed and compared quantitatively based on the predicted von Mises stress, displacement and effective strain. The maximum von Mises stress of each component in both models was lower than the yield strength of respective material, while the predicted results of nonlinear anisotropic model were generally below to those of the linear elastic isotropic model. Furthermore, the maximum von Mises stress of natural vertebra and reconstructed system was decreased by 2-37MPa and 20-61MPa, respectively. The maximum reductions for the translation displacement of the artificial vertebral body implant and motion range of whole model were reached to 0.26mm and 0.77°. The percentage of effective strain elements on the superior and inferior endplates adjacent to implant was diminished by up to 19.7% and 23.1%, respectively. After comprehensive comparison, these results indicated that the finite element model with the assumption of linear elastic isotropy may underestimate the safety of the reconstruction system, while misdiagnose higher stability by overestimating the range of motion and bone growth capability.

FRACTURE ANALYSIS AND SHIELDING EFFECTS IN ADVANCED MATERIALS

Due to their ability to interconnect electrical and mechanical domains, piezoelectric materials are increasingly finding applications in advanced electromechanical systems. Notably, magneto-electric composites like BaTiO3-CoFe2O4 have emerged as vital materials for the next generation of devices. Exploring this realm is a complex and significant endeavor, demanding the attention of the scientific community and further research. Over recent decades, the scope of formulating and executing computational models for continuous media has substantially broadened, encompassing a diverse array of material properties and fields in computational models. This article centers on the utilization of asymptotic analysis as a mathematical tool for constructing approximate equations and assessing the relevance of various hypotheses. It delves into the utilization of the perturbation method, pioneered by Kagadiy T. S. and others, to tackle two-dimensional contact problems in electropelasticity, particularly in the context of materials with linear anisotropy. The extensive applicability of this asymptotic approach underscores its efficacy in simplifying intricate problems by breaking them down into a sequence of boundary problem resolutions grounded in the theory of potentials. The collaborative effort of the authors in this research underscores that employing the mentioned method opens up avenues for formulating pertinent boundary problems for the fundamental equations. This, in turn, allows for the representation of the initial electropelasticity problem as a superposition of more manageable boundary problems. While mechanical and electrical components can be treated separately, they still interact via boundary conditions. To conduct a numerical analysis, the article examines scenarios where one crack surface slides parallel to the crack front against another and selects relevant materials with known characteristics. Calculations reveal that, even in the absence of mechanical load, crack surfaces undergo relative sliding due to non-zero electrical or magnetic fields. The study of the shielding effect, which mitigates crack motion by altering magnetic field distribution, holds particular significance. This effect reduces the overall stress intensity factor and impedes crack propagation. Conducting such a comprehensive analysis is pivotal for comprehending and foretelling the strength and reliability of structural components composed of piezoelectric and piezomagnetic materials. It is imperative to conduct a thorough examination of the mechanisms governing their failure.

Tunable Anisotropic Extrinsic Self‐Trapped Exciton Emission in Van Der Waals Layered In4/3P2S6

AbstractSelf‐trapped exciton (STE) induced broad‐band emission (BE) has sparked considerable interest due to its potential applications in white‐light emitters and optoelectronics. This phenomenon is widely observed in organic–inorganic hybrid perovskites with soft lattice structures, and its physical origin is still under debate. Herein, strong sub‐bandgap STE emission with a large Stokes shift and a photoluminescence quantum yield of up to 9.2% in van der Waals (vdW) layered In4/3P2S6 is reported. Combining comprehensive optical characterizations and theoretical calculations, this concludes that defect‐assisted extrinsic STE is responsible for the BE. The excitonic state can be further localized by hydrostatic pressure, resulting in a threefold PL intensity enhancement. In addition, angle‐resolved polarized Raman demonstrates the anisotropic lattice dynamics in IPS, which may underpin the highly linear anisotropy of the STE emission. This work clarifies the defect, STE, and anisotropy coupling effect in vdW crystal, and provides innovative avenues to modulate the STE luminescence.

Emergence and inversion of chirality in hierarchical assemblies of CdS nanocrystal fibers.

Arranging semiconducting nanocrystals into ordered superstructures is a promising platform to study fundamental light-matter interactions and develop programmable optical metamaterials. We investigated how the geometrical arrangement of CdS nanocrystals in hierarchical assemblies affects chiroptical properties. To create these structures, we controlled the evaporation of a colloidal CdS nanocrystal solution between two parallel plates. We combined in situ microscopy and computational modeling to establish a formation mechanism involving the shear-induced alignment of nanocrystal fibers and the subsequent mechanical relaxation of the stretched fibers to form Raman noodle-type band textures. The high linear anisotropy in these films shares many similarities with cholesteric liquid crystals. The films deposited on top and bottom surfaces exhibit opposite chirality. The mechanistic insights from this study are consequential to enable future advances in the design and fabrication of programmable optical metamaterials for further development of polarization-based optics toward applications in sensing, hyperspectral imaging, and quantum information technology.

GW_CLASS: Cosmological Gravitational Wave Background in the cosmic linear anisotropy solving system

The anisotropies of the Cosmological Gravitational Wave Background (CGWB) retain information about the primordial mechanisms that source the gravitational waves and about the geometry and the particle content of the universe at early times. In this work, we discuss in detail the computation of the angular power spectra of CGWB anisotropies and of their cross correlation with Cosmic Microwave Background (CMB) anisotropies, assuming different processes for the generation of these primordial signals. We present an efficient implementation of our results in a modified version of CLASS which will be publicly available. By combining our new code GW_CLASS with MontePython, we forecast the combined sensitivity of future gravitational wave interferometers and CMB experiments to the cosmological parameters that characterize the cosmological gravitational wave background.

Phase stability diagram, self-similar structures, and multistability in a free-running VCSEL with a small misalignment between the phase and amplitude anisotropies.

We report on the global dynamics of a free-running vertical-cavity surface-emitting laser (VCSEL) with misalignment between the linear phase and amplitude anisotropies due to the fact that this case might occur in practice caused unintentionally by minor manufacturing variations or design, in virtue of high-resolution phase stability diagrams, where two kinds of self-similar structures are revealed. Of interest is that the Arnold tongue cascades covered by multiple distinct periodicities are discovered for the first time in several scenarios specified in the free-running VCSEL, to the best of our knowledge. Additionally, we also uncover the existence of multistability through the basin of the attraction, as well as the eyes of anti-chaos and periodicity characterized by fractal. The findings may shed new light on interesting polarization dynamics of VCSELs, and also open the possibility to detect the above-mentioned structures experimentally and develop some potential applications.

Characterization of membrane-interaction mechanisms of proteins using vacuum-ultraviolet circular dichroism spectroscopy.

Protein-membrane interactions play an important role in various biological phenomena, such as material transport, demyelinating diseases, and antimicrobial activity. We combined vacuum-ultraviolet circular dichroism (VUVCD) spectroscopy with theoretical (e.g., molecular dynamics and neural networks) and polarization experimental (e.g., linear dichroism and fluorescence anisotropy) methods to characterize the membrane interaction mechanisms of three soluble proteins (or peptides). α1 -Acid glycoprotein has the drug-binding ability, but the combination of VUVCD and neural-network method revealed that the membrane interaction causes the extension of helix in the N-terminal region, which reduces the binding ability. Myelin basic protein (MBP) is an essential component of the myelin sheath with a multi-layered structure. Molecular dynamics simulations using a VUVCD-guided system showed that MBP forms two amphiphilic and three non-amphiphilic helices as membrane interaction sites. These multivalent interactions may allow MBP to interact with two opposing membrane leaflets, contributing to the formation of a multi-layered myelin structure. The antimicrobial peptide magainin 2 interacts with the bacterial membrane, causing damage to its structure. VUVCD analysis revealed that the M2 peptides assemble in the membrane and turn into oligomers with a β-strand structure. Linear dichroism and fluorescence anisotropy suggested that the oligomers are inserted into the hydrophobic core of the membrane, disrupting the bacterial membrane. Overall, our findings demonstrate that VUVCD and its combination with theoretical and polarization experimental methods pave the way for unraveling the molecular mechanisms of biological phenomena related to protein-membrane interactions.

Can we still measure circular dichroism with circular dichroism spectrometers: The dangers of anisotropic artifacts.

Chiral materials with strong linear anisotropies are difficult to accurately characterize with circular dichroism (CD) because of artifactual contributions to their spectra from linear dichroism (LD) and birefringence (LB). Historically, researchers have used a second-order Taylor series expansion on the Mueller matrix to model the LDLB interaction effects on the spectra in conventional materials, but this approach may no longer be sufficient to account for the artifactual CD signals in emergent materials. In this work, we present an expression to model the measured CD using a third-order expansion, which introduces "pairwise interference" terms that, unlike the LDLB terms, cannot be averaged out of the signal. We find that the third-order pairwise interference terms can make noticeable contributions to the simulated CD spectra. Using numerical simulations of the measured CD across a broad range of linear and chiral anisotropy parameters, the LDLB interactions are most prominent in samples that have strong linear anisotropies (LD, LB) but negligible chiral anisotropies, where the measured CD strays from the chirality-induced CD by factors greater than 103 . Additionally, the pairwise interactions are most significant in systems with moderate-to-strong chiral and linear anisotropies, where the measured CD is inflated twofold, a figure that grows as linear anisotropies approach their maximum. In summary, media with moderate-to-strong linear anisotropy are in great danger of having their CD altered by these effects in subtle manners. This work highlights the significance of considering distortions in CD measurements through higher-order pairwise interference effects in highly anisotropic nanomaterials.

Spin vertical-cavity surface-emitting lasers with linear gain anisotropy: Prediction of exceptional points and nontrivial dynamical regimes

It is shown that when the linear gain anisotropy is properly accounted for, spin-injected vertical-cavity surface-emitting lasers (spin-VCSELs) offer interesting functionalities. Using the extended spin-flip model (SFM), we predict the existence of exceptional points (EPs) in spin-VCSELs and two interesting phenomena which accompany EPs, namely, (i) the polarization switching manifesting as induced change of field helicity sign and (ii) frequency comb generation without the need of external injection locking. Both effects have tremendous technological potential such as fast on-chip polarization switching, and most importantly, their concepts are not limited only to spin-VCSEL technology. We discuss the concept of anisotropy-engineered non-Hermitian microlasers and we provide a theoretical background to study their polarization dynamics near EPs.

Strong anisotropic optical response in two-dimensional Mo-VIA and Mo-VIIA monolayer binary materials

Two-dimensional binary materials based on transition metals have attracted much research attention because of their intriguing physical properties owing to their crystalline structure. The optical response of these compounds paves a way to manipulate the optical and electronic properties for optical and electronic device applications. Here, the frequency-dependent anisotropic linear optical response of eight molybdenum (Mo)-based binary materials from the VIA (i.e., O, S, Se, and Te) and VIIA (i.e., F, Cl, Br, and I) groups are systematically investigated using first-principles density functional theory. These binary materials exhibit strong linear anisotropic dielectric and optical behavior in the low energy range and become isotropic at high energies. The linear anisotropy in optical functions can be attributed to the intralayer excitonic behavior. The phenomenon of birefringence is the main characteristic of anisotropic materials. The dichroic ratio determines the degree of anisotropy. Among these binary materials, MoS2 and MoCl2 show large birefringence in the visible and far-infrared regions. The birefringence in these materials is also compared with other reported materials. Birefringence is critical for light manipulation during propagation through media. The present results provide insight into the linear optical anisotropies of the binary materials considered. Furthermore, the results suggest that these Mo-based binary materials could be potential candidates for developing optical instruments, optoelectronic, and photonic device applications.

Macroscopic mapping of the linear in-plane anisotropy of nanocellulosic thin films by Mueller matrix polarimetry

The present work focuses on the characterization of the macroscopic optical anisotropy of cellulose nanocomposite multilayer thin films prepared by grazing incidence spraying. The polarization properties of such films composed of in-plane aligned cellulose nanofibrils embedded in a polyelectrolyte multilayer are investigated by Mueller matrix polarimetry (MMP). Linear birefringence is the predominant polarization property resulting from the unidirectional organization of the cellulose nanofibrils, thus, the differential decomposition of the Mueller matrix measured on the films allows the determination of their actual structural birefringence, ⟨Δn⟩=0.032. Moreover, modeling the sample as an effective medium provides a parametrized expression that describes its linear birefringence as a function of the optical constants of the components, the volume fraction of nanofibrils, the distribution of orientation, and the film thickness. Therefore, MMP provides a fast, simple, and non-destructive method to characterize both the structural characteristics and the optical birefringence/dichroism of the films over large areas, which is of great interest for various optoelectronic applications.

Optical anisotropy composition of benign and malignant prostate tissues revealed by Mueller-matrix imaging.

A Mueller matrix imaging approach is employed to disclose the three-dimensional composition framework of optical anisotropy within cancerous biotissues. Visualized by the Mueller matrix technique spatial architecture of optical anisotropy of tissues is characterised by high-order statistical moments. Thus, quantitative analysis of the spatial distribution of optical anisotropy, such as linear and circular birefringence and dichroism, is revealed by using high-order statistical moments, enabling definitively discriminate prostate adenoma and carcinoma. The developed approach provides greater (>90%) accuracy of diagnostic achieved by using either the 3-rd or 4-th order statistical moments of the linear anisotropy parameters. Noticeable difference is observed between prostate adenoma and carcinoma tissue samples in terms of the extinction coefficient and the degree of depolarisation. Juxtaposition to other optical diagnostic modalities demonstrates the greater accuracy of the approach described herein, paving the way for its wider application in cancer diagnosis and tissue characterization.

Conformational Effects of Mutations and Spherical Confinement in Small Peptides through Hybrid Multi‐Population Genetic Algorithms

AbstractIn this work the role of spherical confinement combined with single and block mutations in small peptides on the onset of specific conformational states is analyzed. An intramolecular potential for the polypeptide chain, composed by a bending term plus a Lennard‐Jones type long range potential is proposed. For the intermolecular interaction with the sphere an integrated Lennard‐Jones (LJ) type potential is used between monomers and the sphere surface. To compute the set of minima values for the total intra and intermolecular potential a combination of a multi‐population genetic algorithm and an hybridized Nelder—Mead simplex algorithm are used, that yield to a larger degree of precision in the prediction of the set of minima potential energy values. To characterize the conformational states of the peptides the gyration tensor, radius of gyration, the asphericity, and the linear anisotropy are computed, and the influence of single‐point and block mutations on the most energetically stable conformations are assed. Results suggest that the spherical confinement does have a significant influence of the polymer conformations; and single‐point mutations introduced along the chain also have a prominent role on peptide's folded states. This opens up the possibility to targeted‐designed peptides with particular and desired properties upon folding.

Linear unit BN2: a novel birefringence-enhanced fundamental module with sp orbital hybridization.

Inorganic planar π-conjugated groups are advantageous to generate large birefringence in optical functional materials, and many excellent materials contain CO3, BO3 or B3O6, such as CaCO3, α/β-BaB2O4 (α/β-BBO), and KBe2BO3F2 (KBBF). In view of their microscopic structures, the common characteristics are the planar structures, which are regarded as birefringence-enhanced fundamental modules (FMs). Nowadays, exploring novel birefringence-enhanced FMs is becoming a burning issue. Herein, we investigated the birefringence-enhanced FMs in B–N systems and found that the BN2 linear unit could produce great birefringence. Through the investigation based on the Inorganic Crystal Structure Database, some compounds with the BN2 linear group were screened out with the formulas A3BN2 (A = Li, Na), A3BN3 (A = Mg, Ca), and Ba3(BN2)2. Particularly, Ca3(BN2)N exhibits a great birefringence of about 0.411 at 1064 nm, which is 3.5, 2.5 and 2.0 times those of the most commercially used birefringent crystals α-BaB2O4 (Δn = 0.116 at 1064 nm), CaCO3 (Δn = 0.164 at 1064 nm) and YVO4 (Δn = 0.208 at 1064 nm), respectively. To find the origins of the optical properties of compounds with the BN2 linear group, the first-principles, REDA and polarizability anisotropy analysis methods were used. Owing to the structural arrangement and the polarization anisotropy of the BN2 linear group, it can influence the birefringence significantly. This work will provide a general way for exploring birefringence-enhanced FMs in B–N compounds.

Electrically rotated retarder/diattenuator system for application to a variety of polarization elements

This study presents an optical system equivalent to a polarization element, which can be applied as a linear phase retarder with arbitrary phase retardation or a linear diattenuator with arbitrary diattenuation. The principal axis of the equivalent polarization element can be rotated by applying an electrical signal to an electro-optic modulator. The simple optical system setup is only composed of three polarization elements in a round-trip configuration. The proposed system is versatile, in that it can be applied to a variety of polarization elements that have linear anisotropy.

Intensity and anisotropies of the stochastic gravitational wave background from merging compact binaries in galaxies

We investigate the isotropic and anisotropic components of the Stochastic Gravitational Wave Background (SGWB) originated from unresolved merging compact binaries in galaxies. We base our analysis on an empirical approach to galactic astrophysics that allows to follow the evolution of individual systems. We then characterize the energy density of the SGWB as a tracer of the total matter density, in order to compute the angular power spectrum of anisotropies with the Cosmic Linear Anisotropy Solving System (CLASS) public code in full generality. We obtain predictions for the isotropic energy density and for the angular power spectrum of the SGWB anisotropies, and study the prospect for their observations with advanced Laser Interferometer Gravitational-Wave and Virgo Observatories and with the Einstein Telescope. We identify the contributions coming from different type of sources (binary black holes, binary neutron stars and black hole-neutron star) and from different redshifts. We examine in detail the spectral shape of the energy density for all types of sources, comparing the results for the two detectors. We find that the power spectrum of the SGWB anisotropies behaves like a power law on large angular scales and drops at small scales: we explain this behavior in terms of the redshift distribution of sources that contribute most to the signal, and of the sensitivities of the two detectors. Finally, we simulate a high resolution full sky map of the SGWB starting from the power spectra obtained with CLASS and including Poisson statistics and clustering properties.

In-plane anisotropic 2D CrPS4 for promising polarization-sensitive photodetection

Polarized photodetectors have been widely used in military and civilian applications. The investigation of promising two-dimensional materials with low symmetry structures will be of great significance for the development of polarized integrated nanodevices. In this work, chromium thiophosphate (CrPS4), a ternary layered semiconductor with low symmetry puckered structures and unique linear dichroism (LD) conversion behavior is introduced to act as a polarization-sensitive photodetector. Angle-resolved polarized Raman spectra (ARPRS), polarization-resolved photoluminescence (PL) spectra, polarization-resolved absorption spectroscopy (PRAS), and electrical transport measurement systematically indicate intriguing anisotropic optical and electrical properties in 2D (two-dimensional) CrPS4. The photodetector of CrPS4 shows a linear anisotropy ratio of ≈1.33 with 405 nm illumination. This pioneering research not only stimulates interest in the development of novel anisotropic 2D materials but also enriches the family of polarization-sensitive photodetectors.