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We present a detailed theoretical analysis of polarized absorption spectra and linear dichroism of cyanine dye aggregates whose unit cells contain two molecules. The studied threadlike ordered system with a molecular exciton delocalized along its axis can be treated as two chains of conventional molecular aggregates, rotated relative to each other at a certain angle around the aggregate axis. Our approach is based on the general formulas for the effective cross section of light absorption by a molecular aggregate and key points of the molecular exciton theory. We have developed a self-consistent theory for describing the orientational effects in the absorption and dichroic spectra of such supramolecular structures with nonplanar unit cell. It is shown that the spectral behavior of such systems exhibits considerable distinctions from that of conventional cyanine dye aggregates. They consist in the strong dependence of the relative intensities of the J- and H-type spectral bands of the aggregate with a nonplanar unit cell on the angles determining the mutual orientations of the transition dipole moments of constituting molecules and the aggregate axis as well as on the polarization direction of incident light. The derived formulas are reduced to the well-known analytical expressions in the particular case of aggregates with one molecule in the unit cell. The calculations performed within the framework of our excitonic theory combined with available vibronic theory allow us to quite reasonably explain the experimental data for the pseudoisocyanine bromide dye aggregate. [ABSTRACT FROM AUTHOR]

This study shows that magnetic linear dichroism (MLD) measurement has great potential for characterizing magnetic nanoparticles (MNPs) used in recently developing biomedical applications or nanoscale mechanical measurement techniques. MLD of MNP suspension reflects the orientation of the MNP. We investigated the frequency dependence of the MLD of MNP suspension under a simple AC field and the effect of the MNP size and material. Under an AC field with the frequency f, the MLD oscillated with 2f for every MNP. The amplitude and phase of this 2f-oscillation were precisely measured with a lock-in amplifier, and we showed the MLD2f frequency spectrum, a plot of real and imaginary parts of the 2f-component of MLD as a function of f. We found that the shape of the MLD2f frequency spectrum can distinguish the rotational modes of MNPs in an AC field. Therefore, this spectrum is helpful for the selection of MNPs for each technique mentioned above. We propose two model functions to fit the MLD2f frequency spectra, consistent with each rotational mode. It is shown that one of the fitting parameters τ0 is associated with the rotational Brownian relaxation time of MNP, and the other parameter β would represent the distribution of the anisotropy energy. The frequency dependence of MLD will provide precise insights into the magnetization and orientational dynamics of the MNP in liquid. [ABSTRACT FROM AUTHOR]

Using linear dichroism theory, one would assume that a z-cut of a uniaxial crystal is equivalent to an x-cut to determine the perpendicular component of the dielectric tensor and the corresponding oscillator parameters. However, Fresnel's equations show that the effect of interfaces in the form of the continuity relations of the different components of the electric field must be considered. A consequence of the continuity relations is that perpendicular modes increase less significantly in strength with increasing angle of incidence than expected. This is a consequence of the fact that it is the inverse of the perpendicular component of the dielectric function that increasingly becomes important with a growing angle of incidence. An inverse dielectric function, however, has typically much smaller values than the dielectric function. An additional consequence is that perpendicular modes are blueshifted and coupled in such a way that oscillator strength is transferred to the higher wavenumber mode. Thus, the spectral signatures of perpendicular modes are often weak and masked by the parallel modes when two modes overlap. Accordingly, to enable dispersion analysis, it is suggested to use a hybrid of the conventional residual sum of squares and the two-trace two-dimensional (2T2D) smart error sum, which can correct systematic multiplicable errors in the experimental spectrum. As demonstrated for fresnoite (Ba2TiSi2O8), this is an important step toward determining the perpendicular component of the dielectric tensor and the corresponding oscillator parameters using dispersion analysis, since asynchronous 2T2D correlation spectra are, in particular, sensitive to perpendicular modes. [ABSTRACT FROM AUTHOR]

Material anisotropy and chirality produce polarization‐dependent light‐matter interactions. Absorption leads to linear and circular dichroism, whereas elastic forward scattering produces linear and circular birefringence. Here a form of dichroism and birefringence is highlighted whereby generic anisotropic media display locally different absorption and scattering of a focused vortex beam that depends upon the sign of the topological charge ℓ$\ell$. The light‐matter interactions described in this work manifest purely through dominant electric‐dipole coupling mechanisms and depend on the paraxial parameter to first‐order. Previous topological‐charge‐dependent light‐matter interactions require the significantly weaker higher‐order multipole moments and are proportional to the paraxial parameter to second‐order. The result represents a method of probing the nano‐optics of advanced materials and the topological properties of structured light. [ABSTRACT FROM AUTHOR]

The polarization of light can provide abundant information regarding the polarization degree, phase shift, and Jones vector, which is important in light communication, environmental scanning, quality inspection, etc. Recently, two-dimensional (2D) semiconductors have provided an ideal platform for detecting polarized light due to their remarkable and tunable linear dichroism (LD). However, the physical mechanism of the in-plane LD in 2D semiconductors has not been systematically investigated, limiting the further exploration of the 2D anisotropic semiconductors and the directionality of experiments on polarization photodetection. In this study, the in-plane LD of 100 types of 2D semiconductors composed of main group elements is investigated via first-principles theory combined with the decision tree algorithm and experimental measurement. The in-plane asymmetry of the lattice and band edge wavefunctions are the main origins of the in-plane LD. 2D semiconductors with in-plane orthorhombic and monoclinic lattices tend to have considerable in-plane LD, while their hexagonal counterparts are optically isotropic. Specifically, orthorhombic 2D semiconductors possess larger in-plane LD because their intrinsic mirror planes in the lattice induce in-plane parity of the wavefunctions at the band edges. The decision tree algorithm further reveals that in-plane LD is also related to the difference for the a and b lattice constants and the electronegativity difference between the cation and anion. In addition, heterostructures formed from these 2D semiconductors exhibit high light absorption, strong in-plane LD, and various types of band alignment. The result of our study can promote the application and development of 2D semiconductors in polarization optoelectronics. [ABSTRACT FROM AUTHOR]

We explore how strain impacts the band structure of metallic-phase VO2 thin films deposited on TiO2(101) substrates. Employing a combination of X-ray absorption linear dichroism and valence band measurements, we demonstrate that strain can alter the intrinsic band structure anisotropy of metallic VO2. Our findings reveal that reducing the thickness of VO2 films leads to a more isotropic band structure. This observation is further supported by an analysis of the electronic population redistribution in the d || − π * bands, which affects the screening length and induces effective mass renormalization. Overall, our results underscore the potential of strain manipulation in tailoring the electronic structure uniformity of thin films, thereby expanding the scope for engineering VO2 functionalities. In this article we studied the evolution of band anisotropy in strained VO2(101) thin films. We found out that strain works as a control agent for the anisotropy and thus controls the features of VO2 bands structure. For this crystal orientation a large strain corresponds to a more homogeneous electronic structure of VO2. This impacts the electrons population redistribution between d|| and π bands, the screening length and the effective mass. By controlling the anisotropy and the band structure properties our results can ease the integration of VO2 into complex electronics. [ABSTRACT FROM AUTHOR]

Electropolymerization is a convenient way to obtain conducting polymers (CPs) directly adhered to an electrode surface. CPs are well-known for their various application fields in photovoltaic cells, chemical sensors, and electronics. By implementing chirality into a CP, the application possibilities will spread further onto chiral sensors or optoelectronics. In this work, we introduce a new inherently chiral polymer based on a macrocyclic 3,4-ethylenedioxythiophene-diketopyrrolopyrrole-3,4-ethylenedioxythiophene triad (EDOT-DPP-EDOT) fused by 1,4-phenylene groups, which was prepared via oxidative electropolymerization directly on the electrode surface. The investigation of the chiroptical properties was performed by circular dichroism spectroscopy in the solid state. The enantiomeric pure polymer films obtained showed dissymmetry factors of up to −2.71 × 10−4, whereby linear dichroism contributions can be widely excluded. [ABSTRACT FROM AUTHOR]

Copper oxide high-temperature superconductors, such as Bi2Sr2CaCu2O8+δ (Bi2212), have garnered extensive research interest due to their high critical temperatures (Tc) surpassing the Bardeen–Cooper–Schrieffer (BCS) limit. The two-dimensional CuO₂ plane is widely regarded as the most crucial element of high-Tc cuprate superconductors. The anisotropy of this CuO₂ layer remains a topic of ongoing interest. Although a few experimental results have reported strong optical anisotropy in both ab and ac-planes of Bi2212 through optical "reflectivity" measurements, there is a lack of studies focusing on the optical anisotropy of these materials using optical "transmittance" measurements by utilizing ultraviolet and visible light. Using a generalized high-accuracy universal polarimeter, we observed significant linear birefringence and linear dichroism peaks in the UV region at room temperature. To investigate the origin of the significant optical anisotropy, single crystals of Bi2−xPbxSr2CaCu2O8+δ with different lead contents (x = 0, 0.4, and 0.6) were grown using the floating zone method, and the wavelength dependencies of linear birefringence and linear dichroism along the c axis were measured. The insights gained into the optical anisotropy of Bi2−xPbxSr2CaCu2O8+δ from this study are significant for discussing its origin of the mechanism of high-Tc superconductivity. [ABSTRACT FROM AUTHOR]

A contribution of free charge carriers in an ensemble of anisotropic silicon nanocrystals to the optical properties in the infrared region has been numerically analyzed. Utilizing a generalized effective medium model that accounts for the shape anisotropy of silicon nanocrystals and mobile charge carriers the reflectance, absorption, and transmittance were found to be strongly dependent on the concentration of free charge carriers. For charge carrier (hole) concentrations ranging from 10 16 to 10 20 c m - 3 , significant birefringence and linear dichroism (absorption anisotropy) are observed, along with a non-monotonic dependence of the refractive index and transmittance coefficients for perpendicular polarization directions. The simulation results align well with experimentally measured transmittance spectra of in-plain anisotropic porous silicon films prepared electrochemically from heavily boron-doped (110)-oriented crystalline silicon wafers. Furthermore, the obtained results are discussed in view potential applications in all-silicon based optical switches and modulators and other active elements of the silicon photonics. [ABSTRACT FROM AUTHOR]

Optical field enhancement maximization has been the ultimate objective of applications covering random lasers, spectroscopy, and ‐importantly‐ targeted drug delivery. Consequently, scientists resorted to plasmonic based approaches, which rendered the entire approach inapplicable due to biodegradability concerns. In another work, an experimental realization for a method of magneto‐optical transmission maximization is reported. However, possible limitations on the higher excitation power needed for biomedical applications are still questionable. Furthermore, a comprehensive, quantitative understanding of all material and design related parameters influencing this enhancement is still needed for complete control over possible applications. Therefore, successfully derives a model for the magneto‐optical transmission under a time‐varying 0–4 kHz magnetic field, exhaustively accounting for material and design related phenomena; birefringence of hematite, dissipation, randomness, and anisotropy on the dielectric function, scattering cross‐section, and polarizability, for the first time. The model achieves an accuracy of 99.99% over the band 300–1100 nm and exhausts the model limitations to the decay time constant of Cotton–Mouton co‐effects. The dynamics of the problem are also derived, accounting for the influence of the magnetic field on the viscosity of the ferrofluid, which leads to an in‐depth, required understanding of the magneto‐optic interactions with ferrofluids for efficient applicability. [ABSTRACT FROM AUTHOR]

Weyl semimetal (WSM) states can be achieved by breaking spatial‐inversion symmetry or time reversal symmetry. However, the anisotropy of the energy reduction contributing to the emergence of WSM states has seldom been investigated by experiments. A van der Waals metal MoTe2 exhibits a type‐II WSM phase below the monoclinic‐to‐orthorhombic‐phase‐transition temperature Tc ∼ 250 K. Here, a combined linearly polarized optical‐spectroscopy and electrical‐transport study of MoTe2 is reported at different temperatures. The Drude components in the a‐axis, b‐axis, and c‐axis optical conductivity spectra, together with the metallic out‐of‐plane and in‐plane electrical resistivities, indicate the coherent inter‐layer and in‐plane charge transports. Moreover, the Drude weight in σ1a(ω), rather than the Drude weights in σ1b(ω) and σ1c(ω), decreases dramatically below Tc, which exhibits a highly anisotropic decrease in its Drude weight and thus suggests a strongly anisotropic reduction of the electronic kinetic energy in the WSM phase. Furthermore, below Tc, due to the in‐plane anisotropic spectral‐weight transfer from Drude component to high‐energy region, the in‐plane inter‐band‐absorption anisotropy increases remarkably ≈770 meV, and has the largest value (≈0.68) of normalized linear dichroism among the reported type‐II WSMs. The work sheds light on seeking new WSMs and developing novel photonic devices based on WSMs. [ABSTRACT FROM AUTHOR]

Full‐Stokes polarization‐resolved photonic artificial synapse (PAS) devices with in‐sensor computing capabilities show great potential for multimode vision perception and processing. However, current polarization‐resolved PAS devices are limited to monotonic recognition of linearly polarized light or circularly polarized light. Here, the study develops a chiral perovskite nanowire‐based PAS device as a full‐Stokes polarimeter to achieve polarization‐dependent neuromorphic optoelectronics. The device demonstrates a significantly high circular dichroism of over 400 millidegree and intrinsic linear dichroism, contributing to effectively sensing polarized light. Efficient charge separation at the perovskite NW/MXene heterostructure results in a prolonged carrier lifetime, thereby achieving a high responsivity of 2.3 AW−1, excellent synaptic behavior, and low power consumption of 0.5 pJ per synaptic stimuli. Significantly, the polarization‐modulated reservoir computing is developed based on the full‐Stokes PAS device, which exhibits a low normalized root mean square error of 0.023 in the chaotic system forecasting task. The single‐nanowire PAS device with the capability of sensing full‐Stokes parameters demonstrates great significance in building advanced energy‐efficient polarization‐resolved nanoscale neuromorphic vision systems. [ABSTRACT FROM AUTHOR]

Revealing transient electronic properties in anisotropic 2D materials is a prerequisite for developing ultrafast optoelectronic functional devices. Here, the ultrafast electronic dynamics of polarization anisotropy for the AB‐stacked rhenium disulfide (ReS2) are studied using time‐ and energy‐resolved photoemission electron microscopy. The ultrafast electronic relaxation process exhibits sensitive layer‐dependent polarization anisotropy. The linear dichroism of the ultrafast electronic dynamics is also measured, indicating that the polarization anisotropy is determined by the fast process on the sub‐picosecond scale. With ab initio theory calculations, it is confirmed that the ultra‐sensitive layer dependence of the lifetime of the fast process originates from a stronger interlayer coupling in the K‐Γ direction (along the b‐axis) of ReS2. Further, by analyzing the time‐resolved photoemission energy spectrum, distinct "fast" and "slow" regimes are found in the ultrafast dynamics of excited electrons with different energies. The corresponding energy windows also show substantial polarization anisotropy, which is associated with the linear dichroism of the electron‐phonon coupling in the AB‐stacked ReS2. This work has implications for the design of angle‐sensitive optoelectronic functional devices with the AB‐stacked ReS2. [ABSTRACT FROM AUTHOR]

We present a method of laser frequency stabilization based on the linear dichroism signal in a transverse magnetic field. This method is similar to the DAVLL (Dichroic Atomic Vapor Laser Lock) method. It differs from DAVLL and from its existing modifications primarily by the fact that it uses signals of linearly polarized light caused by alignment, rather than circular refraction caused by orientation, and therefore allows us to obtain error signals at the magnetic field modulation frequency (or its second harmonic) by extremely simple means. The method allows the laser frequency to be stabilized in the vicinity of the low-frequency transition in the D1 line of Cs; it does not require strong magnetic fields or careful shielding of cells containing cesium atoms. Although the absorption line in a gas-filled cell is typically gigahertz wide, the achievable resolution, limited by the signal-to-noise ratio of photon shot noise, can reach units or tens of kilohertz in a one hertz bandwidth. [ABSTRACT FROM AUTHOR]

Ultrathin titanium nitride (TiN) is a novel material platform for constructing active metasurfaces in the near-infrared region (NIR). Here, we realized tunable polarization-selective absorption by gating ultrathin TiN in an Ultrathin TiN Grating Metasurface (UTGM) and a gold resonator/TiN film Hybrid Metasurface (GTHM), respectively. The TM wave absorption (0.96) was much larger than that of the TE wave in the UTGM. When the carrier density decreased by 12%, the near-perfect TM absorption peak blue-shifted by 0.3 μm. Similarly, the linear dichroism (0.96) peak in GTHM blue-shifted by 0.12 μm when gating ultrathin TiN film. Active metasurfaces with tunable polarization-selective absorption have huge potential in dynamic integrated electro-optic devices in NIR. [ABSTRACT FROM AUTHOR]

The LD conversion offers great potential in providing an additional degree of freedom that may be beneficial to novel polarization‐wavelength‐selective detectors and optical switching. However, conventional crystals with optical anisotropy typically show unidirectional LD over a broad wavelength range and the materials with LD conversion behavior remain scarce. Here, by combining angle‐resolved polarized optical absorption measurements and theoretical calculations, this study demonstrates that quasi‐1D Weyl semimetal (TaSe4)2I single crystal shows unique LD conversion phenomenon at the wavelength of 1064 nm. Meanwhile, (TaSe4)2I persists giant linear optical anisotropy due to the intrinsic feature of 1D [TaSe4] chains along the c‐axis. Additionally, the (TaSe4)2I nanoribbon exhibits anisotropic second harmonic generation (SHG). These results hold significant importance to facilitate the development of topological photonics and novel photonic devices applications based on topological semimetals. [ABSTRACT FROM AUTHOR]

In this study, the nonlinear optical phenomena emerging from the interaction between vortex and vector beams and achiral nanoparticles or nanostructures are investigated. Despite the achiral symmetry of the nanostructure, the interplay between the symmetries of the vortex beam, the nanostructure, and the crystalline lattice of the nanostructure material can result in circular dichroism in the nonlinear regime. A formula is derived that describes the conditions for the appearance of circular dichroism across a broad range of scenarios, taking into account all the symmetries. Building on these findings, the conditions for both linear and nonlinear dichroism when illuminated by vector beams have been determined. This work can provide important insights that can enhance the design of chiral sensors and optical traps, making them more versatile and effective. [ABSTRACT FROM AUTHOR]

The ability to freely control the polarization of X‐rays enables measurement techniques relying on circular or linear dichroism, which have become indispensable tools for characterizing the properties of chiral molecules or magnetic structures. Therefore, the demand for polarization control in X‐ray free‐electron lasers is increasing to enable polarization‐sensitive dynamical studies on ultrafast time scales. The soft X‐ray branch Athos of SwissFEL was designed with the aim of providing freely adjustable and arbitrary polarization by building its undulator solely from modules of the novel Apple X type. In this paper, the magnetic model of the linear inclined and circular Apple X polarization schemes are studied. The polarization is characterized by measuring the angular electron emission distributions of helium for various polarizations using cold target recoil ion momentum spectroscopy. The generation of fully linear polarized light of arbitrary angle, as well as elliptical polarizations of varying degree, are demonstrated. [ABSTRACT FROM AUTHOR]

Size-selected linear sp-carbon chain molecules of hydrogen-capped polyyne C12H2 are dispersed in stretched polyvinyl alcohol (PVA) films to align them along the direction of stretching of the film. The order parameter for anisotropic molecular orientation is determined from the angular dependence of UV absorption band intensities using linearly polarized incident light. Phosphorescence spectra at cryogenic temperature of 20 K of aligned C12H2 polyyne molecules in the stretched PVA film exhibit anisotropic properties, namely linearly polarized luminescence (LPL). Molecular orientation is modeled by the | cos ⁡ θ | N distribution of linear molecules to simulate angle-dependent polarized optical emission intensities. The ensemble of aligned polyyne molecules is demonstrated to be an ideal molecular system for consideration of linear dichroism in LPL as well as in photo absorption. [ABSTRACT FROM AUTHOR]

Recently, a technical modification of a Reflectance Anisotropy Spectroscopy (RAS) spectrometer has been proposed to investigate the circular dichroism (CD) of samples instead of the normally studied linear dichroism. CD-RAS measures the anisotropy of the optical properties of a sample under right-handed and left-handed circularly polarized light. Here, we present the application of CD-RAS to measure the circular dichroism of a twisted bilayer of graphene, purposely prepared as a possible substrate for the adsorption of thin molecular layers, in air, in liquid or in a vacuum. This result demonstrates the performance of the apparatus and shows interesting perspectives for the investigation of chiral organic assemblies deposited in solid film. [ABSTRACT FROM AUTHOR]

The anisotropic optical absorption edge of β-Ga2O3 follows a modified Beer–Lambert law having two effective absorption coefficients. The absorption coefficient of linearly polarized light reduces to the least absorbing direction beyond a critical penetration depth, which itself depends on polarization and wavelength. To understand this behavior, a Stokes vector analysis is performed to track the polarization state as a function of depth. The weakening of the absorption coefficient is associated with a gradual shift of linear polarization to the least absorbing crystallographic direction in the plane, which is along the a-exciton within the (010) plane or along the b-exciton in the (001) plane. We show that strong linear dichroism near the optical absorption edge causes this shift in β-Ga2O3, which arises from the anisotropy and spectral splitting of the physical absorbers, i.e., excitons. The linear polarization shift is accompanied by a variation in the ellipticity due to the birefringence of β-Ga2O3. Analysis of the phase relationship between the incoming electric field to that at a certain depth reveals the phase speed as an effective refractive index, which varies along different crystallographic directions. The critical penetration depth is shown to be correlated with the depth at which the ellipticity is maximal. Thus, the anisotropic Beer–Lambert law arises from the interplay of both the dichroic and birefringent properties of β-Ga2O3. [ABSTRACT FROM AUTHOR]

The anisotropic optical absorption edge of β-Ga2O3 follows a modified Beer–Lambert law having two effective absorption coefficients. The absorption coefficient of linearly polarized light reduces to the least absorbing direction beyond a critical penetration depth, which itself depends on polarization and wavelength. To understand this behavior, a Stokes vector analysis is performed to track the polarization state as a function of depth. The weakening of the absorption coefficient is associated with a gradual shift of linear polarization to the least absorbing crystallographic direction in the plane, which is along the a-exciton within the (010) plane or along the b-exciton in the (001) plane. We show that strong linear dichroism near the optical absorption edge causes this shift in β-Ga2O3, which arises from the anisotropy and spectral splitting of the physical absorbers, i.e., excitons. The linear polarization shift is accompanied by a variation in the ellipticity due to the birefringence of β-Ga2O3. Analysis of the phase relationship between the incoming electric field to that at a certain depth reveals the phase speed as an effective refractive index, which varies along different crystallographic directions. The critical penetration depth is shown to be correlated with the depth at which the ellipticity is maximal. Thus, the anisotropic Beer–Lambert law arises from the interplay of both the dichroic and birefringent properties of β-Ga2O3. [ABSTRACT FROM AUTHOR]

Clockwise or counter‐clockwise spin coating? In the current hot research topic of chiral metal‐halide semiconductors, several investigations have been undertaken in order to reveal their natural optical activity and have reported dissymmetry factors (gabs) for thin films of many hybrid compounds, usually without considering the macroscopic anisotropies inherent to solid‐state samples. Yet, CD in the solid state can be strongly modulated by the co‐existence of linear dichroism (LD) and linear birefringence (LB). Theoretical studies recently revealed the importance of such macroscopic interferences in the CD response of solid‐state samples, often referred as symmetric (sLDLB) and antisymmetric (aLDLB) effects. Based on the newly synthesized one‐dimensional lead‐halide networks of formula (S/R‐HP1A)PbBr3 and (S/R‐HP1A)PbI3, an experimental method to accurately discriminate between CD, sLDLB and aLDLB in chiral metal‐halide networks is here presented. The main experimental conditions influencing sLDLB and aLDLB amplitude are also highlighted, such as the concentration of the precursor solution and the spin‐coating rotation direction, finally providing a complete experimental guide for the forthcoming chiroptical investigations of such important family of chiral hybrid materials. [ABSTRACT FROM AUTHOR]

Within angle‐resolved polarized Raman spectroscopy (ARPRS) experiments, ensuring accurate configurations is crucial for obtaining reliable results, especially when dealing with anisotropic materials like CrOCl with anisotropic crystal structure and phonon properties. However, comprehensive understanding of phase‐dependent ARPRS and the calibration of phase angle on anisotropic phonon modes from a crystallographic perspective are still lacking. Herein, detailed investigation on phase‐dependent ARPRS and looked into the anisotropic photo‐phonon interaction in CrOCl through in situ ARPRS is conducted. The Raman tensors and crystal orientation are acquired under two typical configurations. Phase‐dependent ARPRS are thoroughly analyzed for the calibration of analyzer deviation. The anomalous anisotropic response in phase‐dependent ARPRS is closely related to the intrinsic linear dichroism (LD) effect in CrOCl, which is further confirmed by angle‐resolved polarization absorption. Moreover, the strong localized rules for various parallel energy bands of CrOCl have generated anomalous LD conversion effect near 470 nm, which expands the potential application of CrOCl in polarization‐wavelength selected devices. This findings can offer in‐depth comprehension on the anisotropic phonon physics of CrOCl and a feasible approach to utilize phase‐dependent ARPRS for probing the undiscovered abundant photo‐induced effects in low‐symmetry 2D materials. [ABSTRACT FROM AUTHOR]

According to the theoretical model based on the Mueller matrix approach, the experimental electronic circular dichroism (ECD) for thin films of chiral organic dyes can be expressed as the sum of several contributions, two of which are the most significant: 1) an intrinsic component (CDiso) invariant upon sample orientation, reflecting the molecular and/or supramolecular chirality, due to 3D‐chiral nanoscopic structures; 2) a non‐reciprocal component (LDLB) which inverts its sign upon sample flipping, which arises from the interaction of linear dichroism and linear birefringence in locally anisotropic domains, expression of 2D‐chiral micro/mesoscopic structures. In this work, we followed in parallel through ECD and differential scanning calorimetry (DSC) the temperature evolution of the supramolecular arrangements of thin films of five structurally related chiral thiophene‐based oligomers with different LDLB/CDiso ratio. By increasing the temperature, regardless of phase transitions observed by DSC analysis, systems with strong CDiso revealed no changes in the ECD spectrum, while compounds with dominant LDLB contribution underwent a gradual (and reversible) reduction of (apparent) ECD signals. These findings demonstrated that the concomitant occurrence of intrinsic and non‐reciprocal components in the ECD spectrum of thin films of chiral organic dyes is strictly correlated with solid‐state organizations of different stability. [ABSTRACT FROM AUTHOR]

Conventional imaging techniques can only record the intensity of light while polarization imaging can record the polarization of light, thus obtaining a higher dimension of image information. We use the COMSOL software to numerically propose a circular polarization photodetector composed of the dislocated 2-hole Si chiral metasurfaces controlling the circular polarization lights and the HgCdTe (MCT) photodetector chip to detect the intensity of light signals. The chiral metasurfaces can be equated to a significant radiation source of the Z-type current density under the right circularly polarized incidence conditions, which explains the large circular dichroism (CD) of absorption of 95% in chiral photodetectors. In addition, the linear dichroism (LD) of the linear polarization pixel is 0.62, and the extinction ratio (ER) is 21 dB. The full Stokes pixel using the six-image-element technique can almost measure arbitrary polarization information of light at 4 μm operation wavelength. Our results highlight the potential of circular dichroic metasurfaces as photonic manipulation platforms for miniaturized polarization detectors. [ABSTRACT FROM AUTHOR]

The accuracy of approximate methods for calculating linear optical spectra depends on many variables. In this study, we fix most of these parameters to typical values found in photosynthetic light-harvesting complexes of plants and determine the accuracy of approximate spectra with respect to exact calculation as a function of the energy gap and interpigment coupling in a pigment dimer. We use a spectral density with the first eight intramolecular modes of chlorophyll a and include inhomogeneous disorder for the calculation of spectra. We compare the accuracy of absorption, linear dichroism, and circular dichroism spectra calculated using the Full Cumulant Expansion (FCE), coherent time-dependent Redfield (ctR), and time-independent Redfield and modified Redfield methods. As a reference, we use spectra calculated with the exact stochastic path integral evaluation method. We find the FCE method to be the most accurate for the calculation of all spectra. The ctR method performs well for the qualitative calculation of absorption and linear dichroism spectra when the pigments are moderately coupled (∼ 15 c m − 1 ) , but ctR spectra may differ significantly from exact spectra when strong interpigment coupling (> 100 c m − 1 ) is present. The dependence of the quality of Redfield and modified Redfield spectra on molecular parameters is similar, and these methods almost always perform worse than ctR, especially when the interpigment coupling is strong or the excitonic energy gap is small (for a given coupling). The accuracy of approximate spectra is not affected by resonance with intramolecular modes for typical system–bath coupling and disorder values found in plant light-harvesting complexes. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) metasurfaces have emerged as a promising platform for optical field manipulation at the nanoscale. To realize their considerable potential, fast, facile, and scalable manufacturing techniques are needed. Here, we put forward such a technique to transform an isotropic self-organized 2D ensemble of supported Ag nanoparticles (NPs) into a functionalized metasurface with tailor-made patterns of linear dichroism (LD). Nanostructured films comprising densely packed Ag NPs with a wide distribution of their sizes, shapes, and nearest neighbor separations were obtained via vacuum deposition of Ag vapors on a glass substrate at room temperature. Then, under the action of linearly polarized pulsed laser illumination, selective heating and reshaping of NPs are achieved. Thus, depending on the orientation of the corresponding plasmon oscillations in Ag NPs relative to the laser light polarization, permanent spectral holes of different strengths were burnt in the inhomogeneously broadened plasmon band. When probed with the light polarized parallel to the laser light polarization, the spectral hole appears to be much deeper as compared to the spectral hole, probed with the cross-polarized light, thus producing considerable LD in an initially isotropic ensemble of metal NPs. At the laser fluence of 17 mJ/cm2, we achieve an LD magnitude of 20%. By focusing the linearly polarized laser light on the surface with Ag NPs and rotating its polarization in the course of scanning, one can impart arbitrary complicated patterns of LD to the Ag metasurface. Such a pattern may be readily recognized but difficult to reproduce, making it a promising earmark applicable in the fight against counterfeiting. [ABSTRACT FROM AUTHOR]

Germanium diselenide (GeSe2) has recently emerged as a promising material for high‐performance optoelectronic devices due to its high absorption coefficient, wide direct bandgap, and anisotropic electronic properties. For the future applications, it is necessary to understand the dynamic evolution of carriers with ultrafast response. In this work, the transient absorption spectroscopy measurements are performed to study the anisotropic dynamic evolution of GeSe2 under the polarized photoexcitation. It is find that the dynamics exhibit linear dichroism and show a significant Auger recombination process when the photoexcitation is perpendicular to the b‐axis of GeSe2. Using first‐principle and transition dipole moment calculations, it is confirmed that the more carrier localization at Γ point along the Γ‐X (perpendicular to the b‐axis) and increase the Auger recombination. In addition, the Auger recombination coefficient ≈ 1.1×10−31 cm6 s−1 is determined and demonstrated that the defect‐assisted indirect Auger recombination plays a key role in the carrier relaxation process. Through time‐resolved transient absorption spectra, it is further revealed that the ultrafast dynamical evolution of excited state absorption peaks under polarized photoexcitation. These results have implications for improving the quantum efficiency of high‐field polarization‐sensitive optoelectronics. [ABSTRACT FROM AUTHOR]

This study proposes a multifunctional terahertz absorber utilizing graphene and vanadium dioxide as functional materials. By utilizing vanadium dioxide in the metallic state, the device achieves linear dichroism, with a maximum value of 0.8 at 1.75 THz, while in the insulating state, the introduction of graphene strips results in a chiral structure that achieves circular dichroism with tunable values ranging from 0 to 0.59 at 1.535 THz by regulating the graphene's Fermi level. The physical mechanism underlying the differential absorption is explained, and the influence of the device's structural parameters and incident angle on the performance is also investigated. This work provides a practical basis for the development of terahertz functional devices in polarization detection and near-field imaging. [ABSTRACT FROM AUTHOR]

Linearly polarised luminescence (LPL) has a wide range of potential applications giving optical and geometric parameters for oriented lumiphores. In this work we present the first wavelength scanned LPL spectra. Analytes are either oriented on stretched polyethylene films or in flow. Applications of the wavelength-dependence of g-factors are illustrated. [ABSTRACT FROM AUTHOR]

Fluorescence‐detected linear dichroism (FD‐LD) enables one to collect linear dichroism spectra for oriented fluorophores in the presence of other absorbing species and light scattering. The experiment proceeds by scanning the excitation wavelength and using a filter to collect only emitted photons from the fluorophore. Thus, it has the potential to give data with enhanced selectivity and quality. By using a synchrotron radiation light source and fluorescence‐detection, we show data for a range of fluorophores in different orienting environments. Film and flow‐oriented FD‐LD spectra were collected down to 170 nm. Even for flow‐oriented liposomes, we have data collected down to 210 nm. For strongly scattering samples, for example, liposomes, FD‐LD has the clear advantage that scattering is absent for the longer wavelength fluorescence photons. The collimated and smaller beam size of the synchrotron radiation also gives rise to sharper and more well‐defined features in the spectra. [ABSTRACT FROM AUTHOR]

Linear dichroism spectroscopy is used to investigate the structure of RecA family recombinase filaments (RecA and Rad51 proteins) with DNA for clarifying the molecular mechanism of DNA strand exchange promoted by these proteins and its activation. The measurements show that the recombinases promote the perpendicular base orientation of single‐stranded DNA only in the presence of activators, indicating the importance of base orientation in the reaction. We summarize the results and discuss the role of DNA base orientation. [ABSTRACT FROM AUTHOR]

Human Rad51 protein (HsRad51)-promoted DNA strand exchange, a crucial step in homologous recombination, is regulated by proteins and calcium ions. Both the activator protein Swi5/Sfr1 and Ca2+ ions stimulate different reaction steps and induce perpendicular DNA base alignment in the presynaptic complex. To investigate the role of base orientation in the strand exchange reaction, we examined the Ca2+ concentration dependence of strand exchange activities and structural changes in the presynaptic complex. Our results show that optimal D-loop formation (strand exchange with closed circular DNA) required Ca2+ concentrations greater than 5 mM, whereas 1 mM Ca2+ was sufficient for strand exchange between two oligonucleotides. Structural changes indicated by increased fluorescence intensity of poly(dεA) (a poly(dA) analog) reached a plateau at 1 mM Ca2+. Ca2+ > 2 mM was required for saturation of linear dichroism signal intensity at 260 nm, associated with rigid perpendicular DNA base orientation, suggesting a correlation with the stimulation of D-loop formation. Therefore, Ca2+ exerts two different effects. Thermal stability measurements suggest that HsRad51 binds two Ca2+ ions with KD values of 0.2 and 2.5 mM, implying that one step is stimulated by one Ca2+ bond and the other by two Ca2+ bonds. Our results indicate parallels between the Mg2+ activation of RecA and the Ca2+ activation of HsRad51. [ABSTRACT FROM AUTHOR]

We propose a chiral metasurface with tunable circular/linear dichroism based on graphene. When a circularly polarized (CP) wave is incident, the metasurface can achieve circular dichroism at two frequencies. Under the incidence of linearly polarized (LP) wave, the metasurface exhibits linear dichroism. At a frequency of 1.89 THz, the designed metasurface has an absorption rate of over 99% for right-handed circularly polarized (RCP) wave, and 11% for left-handed circularly polarized (LCP) wave. The circular dichroism equals 0.88. At 3.0 THz, while the absorptance of the metasurface for LCP and for RCP waves is 97% and 17%, respectively. The circular dichroism is 0.80. At 0.76 THz, and the absorption rate of the metasurface for x-polarized and y-polarized waves is 0.95 and 0.22, respectively. The linear dichroism is 0.73. The near-field imaging is realized by using the differential characteristics of the circular dichroism metasurface. In addition, imaging resolution, linear/Circular dichroism, and single-/dual-frequency terahertz absorption can be effectively adjusted by changing the Fermi level of graphene. This structure has good application prospects in tunable imaging and tunable dichroism. [ABSTRACT FROM AUTHOR]

2D magnets have recently drawn enormous interest. As an air‐stable A‐type van der Waals antiferromagnet (AFM), CrSBr has attracted great attention but has also led to controversies about its large‐span ordering temperatures. Herein, a systematic study of the magnetic phase transition in single‐crystalline CrSBr with ultrahigh‐quality through surface‐sensitive X‐ray magnetic linear dichroism and X‐ray magnetic circular dichroism measurements combined with vibrating sample magnetometry for characterization of bulk magnetization is reported. The interlayer AFM order of both surface and bulk CrSBr is revealed to maintain a similar Néel temperature within the range of 132–142 K. However, the intralayer ferromagnetic (FM) order of surface CrSBr is found to sustain up to ≈238 K, 70 K higher than the value obtained from the bulk CrSBr, demonstrating a dramatically different surface and bulk Curie temperature in CrSBr. Moreover, a half‐filled t2g electronic state for Cr3+ ions with magnetic moment of ≈3 µB/Cr in CrSBr is clearly identified. These results enrich the understanding of the electronic structure and magnetism in CrSBr, providing this material as a promising building block for future spintronic devices. [ABSTRACT FROM AUTHOR]

Motivated by the imperative demand for design integration and miniaturization within the terahertz (THz) spectrum, this study presents an innovative solution to the challenges associated with singular functionality, limited application scope, and intricate structures prevalent in conventional metasurfaces. The proposed multifunctional tunable metasurface leverages a hybridized grapheme–metal structure, addressing critical limitations in existing designs. Comprising three distinct layers, namely a graphene–gold resonance layer, a Topas dielectric layer, and a bottom gold film reflective layer, this terahertz metasurface exhibits multifunctionality that is both polarization and incident-angle independent. The metasurface demonstrates a broadband circular dichroism (CD) function when subjected to incident circularly polarized waves. In contrast, under linear incidence, the proposed design achieves functionalities encompassing linear dichroism (LD) and polarization conversion. Remarkably, graphene's chemical potential and the incident light's state can be manipulated to tune each functional aspect's intensity finely. The proposed tunable multifaceted metasurface showcases significant referential importance within the terahertz spectrum, mainly contributing to advancing CD metamirrors, chiral photodetectors, polarization digital imaging systems, and intelligent switches. [ABSTRACT FROM AUTHOR]

The discovery of polar liquid crystals, such as ferroelectric and helielectric liquid crystals, provides fascinating platforms for designing and modulating polarisation structures that generate strong second harmonic generation. Here, we report that the helielectric nematics, i.e. the polar cholesteric liquid crystals, realise an unprecedented phase-matching condition for the second harmonic generation in the photonic bandgap. Like the circular dichroism in the linear optical regime, the phase-matched second harmonic generation generated in a helielectric nematic medium exhibits a circular polarisation selectivity in the nonlinear optical regime. The maximum g-factor for the second harmonic generation is over ~ 1.95. [ABSTRACT FROM AUTHOR]

We present a method of laser frequency stabilization based on the linear dichroism signal in a transverse magnetic field. This method is similar to the DAVLL (Dichroic Atomic Vapor Laser Lock) method. It differs from DAVLL and from its existing modifications primarily by the fact that it uses signals of linearly polarized light caused by alignment, rather than circular refraction caused by orientation, and therefore allows us to obtain error signals at the magnetic field modulation frequency (or its second harmonic) by extremely simple means. The method allows the laser frequency to be stabilized in the vicinity of the low-frequency transition in the D1 line of Cs; it does not require strong magnetic fields or careful shielding of cells containing cesium atoms. Although the absorption line in a gas-filled cell is typically gigahertz wide, the achievable resolution, limited by the signal-to-noise ratio of photon shot noise, can reach units or tens of kilohertz in a one hertz bandwidth.

The rich physical properties unveiled in a plethora of transition and rare-earth metal oxides have been attributed to the intricate interplays between the orbital, charge, and spin degrees of freedom. Among them, rare-earth manganites (RMnO3) have been attracting tremendous attention owing to the ionic size-induced lattice distortion dictated by the Goldschmidt tolerance factor and the substantial Jahn–Teller distortion unique to Mn3+ ions, which evidently have resulted in a variety of emergent characteristics in electronic, magnetic, and orbital ordering. In this work, we deliberately engineered the orientation of a series of orthorhombic YMnO3 (o-YMO) films grown on SrTiO3(100) [STO(100)] and SrTiO3(110) [STO(110)] substrates by means of pulsed laser deposition. The x-ray diffraction (XRD) and reciprocal space mapping revealed that o-YMO/STO(100) is c-axis-oriented and o-YMO/STO(110) is a-axis-oriented, respectively. The XRD ϕ-scans further indicate that both films have excellent in-plane crystallinity, allowing the exploration of anisotropies along the respective crystallographic orientations. Indeed, the x-ray absorption linear dichroism spectroscopy taken along the respective crystallographic orientations evidently exhibited substantial anisotropy. Theoretical fitting with configuration interaction cluster calculations suggests that the d 3 z 2 − r 2 orbitals are parallel to YMO[001]/(100), leading to stronger electron scattering along the c-axis. Independent polarization-dependent Δ R/R spectra obtained using the femtosecond pump–probe method exhibited substantial anisotropic behaviors in carrier relaxation dynamics when probing along different crystallographic orientations, presumably due to orbital ordering anisotropies. [ABSTRACT FROM AUTHOR]

We demonstrate both theoretically and experimentally that a linearly polarized optical beam incident on a linearly dichroic nematic liquid crystal cell with a topological defect of the topological strength q and linear dichroism, transforms into a composite vector beam consisting of elementary vector beams with the polarization singularity orders m=2q and m=q. Consequently, it has been proved that due to the linear dichroism a liquid crystal defect of the topological strength q=1 transforms an incident circularly polarized beam into a composite vortex beam consisting of the double-charged vortex beam and vector-vortex beam with polarization order and topological charge that are equal to unity. [ABSTRACT FROM AUTHOR]

Important attention in forensic medical practice is given to the solution of issues that arise during the examination in the case of traumatic brain injury (TBI), as this type of injury leads to high mortality and disability. Conducting an autopsy of the body of the deceased, whose death occurred from a TBI, there are cases when the injury occurs as a result of a fall of a person who previously developed a cerebral infarction, and sometimes vice versa. In this case, it is important to accurately verify the primary cause of death, therefore, timely and objective determination of the time of formation of a hemorrhage in the human brain is necessary. The purpose and tasks of the research. To evaluate the possibility of detecting time of formation of a hemorrhage of traumatic and non-traumatic genesis by the generally accepted histological method and polarization phase microscopy, and to compare their effectiveness. Research materials and methods. For the study, human brain samples were selected from 140 deceased individuals whose deaths occurred between 1 and 3 days after the onset of bleeding, according to medical records. As a control group, human brain samples were selected from 40 individuals who died of coronary heart disease. Light microscopy was performed by preliminary staining of histologic specimens according to the Perls method. Phase polarization tomography of the samples was performed using a Stokes polarimeter. Research Results. Stained human brain preparations of the experimental and control groups were examined and analyzed and it was found that hemosiderin was not present in all experimental samples (only in 31 out of 40 samples were present). It was not possible to establish the corresponding time dependences of the age of the formation of hemorrhages, regardless of the genesis, since the random appearance of the pigment in the experimental samples is noted at different time intervals. Analytical processing of the results of the statistical processing of the topographic structure of tomograms of the anisotropy of linear dichroism of the fibrillar networks of samples of the deceased from the experimental and control groups revealed a wider time range of sensitivity of this method to destructive changes in nervous tissue, in comparison with the polarimetric methods used in previous studies. As a result, there is an accelerated temporal decrease in the absolute values and the range of dispersion of the anisotropy of linear dichroism value with increasing time since the formation of hemorrhage. Conclusions. Polarization-phase microscopy has shown a significant advantage in its use in comparison with the gold standard - the Perls' staining method for determining the time of hemorrhage formation in the human brain. [ABSTRACT FROM AUTHOR]