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In this Tutorial, we overview recent developments to break and manipulate electromagnetic nonreciprocity in two-dimensional (2D) materials without relying on magnetic fields. To this purpose, we provide a general conductivity model to describe gyrotropic metasurfaces that exhibit nonreciprocity through different physical mechanisms enabled by 2D materials, including optical pumping, drifting electrons, ferromagnetic monolayers, mechanical strain, and spatiotemporal modulation. We describe in detail the resulting systems, focusing on near-field phenomena, associated to nonreciprocal bulk and edge surface plasmon propagation, and on far-field responses, related to Faraday/Kerr rotation and optical dichroism of waves propagating in free-space. Additionally, we review and contextualize recent advancements in magnet-free nonreciprocal devices based on 2D materials, ranging from Faraday rotators and optical dichrosim, to plasmonic and photonic isolators, hyperlenses, and tunable optical traps. We conclude by providing our outlook for the future development of this technology and its potential applications in areas such as communications, sensing, wave generation, and spectroscopy, among others. [ABSTRACT FROM AUTHOR]

Arrays and ensembles of chiral nanostructures have potential applications in the field of enantioselective sensors, metamaterials, and metasurfaces. In particular, chiral nanostructures fabricated through chemical and bottom-up approaches have attracted much attention from the viewpoint of cost and scalability, but the heterogeneity of the unit nanostructure constituting the array or ensemble often deteriorates its chiroptical responses. Here, we report that their deteriorated responses can be recovered or even enhanced further by interparticle plasmon coupling. We employed chiral silver (Ag) hexamers as models for electromagnetic simulations and investigated the effect of their parameters, such as interparticle spacing, chiral purity, and enantiomeric excess, on their g-factor, which is an index for chiroptical responses. The maximum value of g-factor (gmax) of the Ag hexamer surpasses that of the chiral monomer and augments with decreasing interparticle spacing. This enhancement in g-factor is observed even when chiral purity and enantiomeric excess are less than 100%, showing the potent role of plasmon coupling in amplifying chiroptical responses. Furthermore, our research highlights the amplification of the effect of plasmon coupling on the gmax value of infinite periodic chiral nanostructures. These results corroborate the potential of plasmon coupling to improve chiroptical responses by precisely controlling the interparticle spacing of chiral plasmonic nanostructures, thus mitigating the loss of g-factor caused by low purity and enantiomeric excess of the nanostructures fabricated by chemical and bottom-up approaches. [ABSTRACT FROM AUTHOR]

Photoelectron angular distributions (PADs) produced from the photoionization of chiral molecules using elliptically polarized light exhibit a forward/backward asymmetry with respect to the optical propagation direction. By recording these distributions using the velocity-map imaging (VMI) technique, the resulting photoelectron elliptical dichroism (PEELD) has previously been demonstrated as a promising spectroscopic tool for studying chiral molecules in the gas phase. The use of elliptically polarized laser pulses, however, produces PADs (and consequently, PEELD distributions) that do not exhibit cylindrical symmetry about the propagation axis. This leads to significant limitations and challenges when employing conventional VMI acquisition and data processing strategies. Using novel photoelectron image analysis methods based around Hankel transform reconstruction tomography and machine learning, however, we have quantified—for the first time—significant symmetry-breaking contributions to PEELD signals that are of a comparable magnitude to the symmetric terms in the multiphoton ionization of (1R,4R)-(+)- and (1S,4S)-(−)-camphor. This contradicts any assumptions that symmetry-breaking can be ignored when reconstructing VMI data. Furthermore, these same symmetry-breaking terms are expected to appear in any experiment where circular and linear laser fields are used together. This ionization scheme is particularly relevant for investigating dynamics in chiral molecules, but it is not limited to them. Developing a full understanding of these terms and the role they play in the photoionization of chiral molecules is of clear importance if the potential of PEELD and related effects for future practical applications is to be fully realized. [ABSTRACT FROM AUTHOR]

We investigate the potential of surface plasmon polaritons at noble metal interfaces for surface-enhanced chiroptical sensing of dilute chiral drug solutions with nl volume. The high quality factor of surface plasmon resonances in both Otto and Kretschmann configurations enables the enhancement of circular dichroism differenatial absorption thanks to the large near-field intensity of such plasmonic excitations. Furthermore, the subwavelength confinement of surface plasmon polaritons is key to attain chiroptical sensitivity to small amounts of drug volumes placed around ≃100 nm by the metal surface. Our calculations focus on reparixin, a pharmaceutical molecule currently used in clinical studies for patients with community-acquired pneumonia, including COVID-19 and acute respiratory distress syndrome. Considering realistic dilute solutions of reparixin dissolved in water with concentration ≤ 5 mg/ml and nl volume, we find a circular-dichroism differential absorption enhancement factor of the order ≃20 and chirality-induced polarization distortion upon surface plasmon polariton excitation. Our results are relevant for the development of innovative chiroptical sensors capable of measuring the enantiomeric imbalance of chiral drug solutions with nl volume. [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]

Capillary force self‐assembly (CFSA) technology unfolds great potential in the fabrication of functional micro/nanostructures. To date, most self‐assembly methods focus on monolithic microstructure manipulation yet it remains a challenge to achieve precise localized control over the CFSA process of micro/nanostructures. Herein, a light‐regulated CFSA is proposed to realize the localized precise control of microstructures, leveraging on the synergistic effect of photothermally‐responsive hydrogel and self‐assembly technique. The micropillars with asymmetric cross‐linking densities can readily prepare by applying a rationally designed laser and laser‐exposing dosage, thereby realizing the on‐demand steering of their bending directions. Significantly, owing to the giant capillary force deriving from the evaporating water, above micropillars can successfully assemble into highly‐ordered chiral structures. Simulation coupling with fundamental hydrodynamics enables to shed light on the light steering principle over pillar's actuations. Last, on the basis of vortical dichroism spectra analysis, the chiral characteristics of light‐regulated self‐assembly including the chiral as well as the achiral self‐assembled microstructures are successfully deployed. This strategy provides an avenue for fabricating the localized controllable self‐assembly at the microscale and will bloom the field over metamaterials, microsensors, chiral optics, and so on. [ABSTRACT FROM AUTHOR]

Nanostructures represent a frontier where meticulous attention to the control and assessment of structural dimensions becomes a linchpin for their seamless integration into diverse technological applications. However, determining the critical dimensions and optical properties of nanostructures with precision still remains a challenging task. In this study, by using an integrative and comprehensive methodical series of studies, the evolution of the depolarization factors in the anisotropic Bruggeman effective medium approximation (AB‐EMA) is investigated. It is found that these anisotropic factors are extremely sensitive to the changes in critical dimensions of the nanostructure platforms. In order to perform a systematic characterization of these parameters, spatially coherent, highly‐ordered slanted nanocolumns are fabricated from zirconia, silicon, titanium, and permalloy on silicon substrates with varying column lengths using glancing angle deposition (GLAD). In tandem, broad‐spectral range Mueller matrix spectroscopic ellipsometry data, spanning from the near‐infrared to the vacuum UV (0.72–6.5 eV), is analyzed with a best‐match model approach based on the anisotropic Bruggeman effective medium theory. The anisotropic optical properties, including complex dielectric function, birefringence, and dichroism, are thereby extracted. Most notably, the research unveils a generalized, material‐independent inverse relationship between depolarization factors and column length. It is envisioned that the presented scaling rules will permit accurate prediction of optical properties of nanocolumnar thin films improving their integration and optimization for optoelectronic and photonic device applications. As an outlook, the highly porous nature and extreme birefringence properties of the fabricated columnar metamaterial platforms are further explored in the detection of nanoparticles from the cross‐polarized integrated spectral color variations. [ABSTRACT FROM AUTHOR]

Here we report on the Magneto‐Chiral Dichroism (MChD) detected through visible and near‐infrared light absorption of two enantiomeric pairs of ErIII and TmIII chiral complexes featuring a propeller‐like molecular structure. The magnetic properties show typical features of isolated paramagnetic ions associated with 4I15/2 and 3H6 ground state terms. MChD spectroscopy shows high gMChD dissymmetry factors of ca. 0.12 T−1 and 0.05 T−1 (T=4.0 K and B=1.0 T) for ErIII and TmIII, respectively, associated with the magnetic‐dipole allowed 4I13/2 ← 4I15/2 and 3H5 ← 3H6 transitions. MChD signals of the two complexes were detected up to room temperature and under magnetic fields up to 5.0 T. For the first time, the MChD results are discussed in the context of the Richardson theory of lanthanide optical activity and provide clear indications on the strongest MChD‐active electronic transitions of lanthanide complexes. [ABSTRACT FROM AUTHOR]

A thin film of thiophene block copolymer composed of 3-dodecylthiophene and 3-benzenesulfonato–thiophene was fabricated by using the friction-transfer method. The benzenesulfonato moiety was transformed by heating to the corresponding sulfonic acid, which induced self-doping. The obtained friction-transfer film showed different morphology from the related cast film. It was also revealed that the film indicated anisotropy parallel/perpendicular toward the drawing direction, which induced absorption dichroism and anisotropy of electric conductivity. [ABSTRACT FROM AUTHOR]

Rotational circular dichroism (RCD) has not been observed yet, but it is expected to deliver information about chiral molecules useful in many branches of chemistry. In the past, rather weak RCD intensities were predicted for model diamagnetic molecules and a limited number of rotational transitions. Here, we review quantum-mechanical foundations and simulate entire spectral profiles, including larger molecules, open-shell molecular radicals, and high-momentum rotational bands. Contribution of the electric quadrupolar moment was considered, but it turned out that it does not contribute to field-free RCD. Two conformers of a model dipeptide provided clearly distinct spectra. The dissymmetry Kuhn parameter gK predicted for the diamagnetic molecules even for high-J transitions rarely exceeded 10−5, and the simulated RCD spectra were often biased to one sign. In the radicals, the coupling of the rotational angular momentum with the spin for some transitions raised gK to about 10−2, and the RCD pattern was more conservative. In the resultant spectra, many transitions had negligible intensities due to small populations of the involved states, and a convolution with a spectral function made the typical RCD/absorption ratios about 100-times smaller (gK ∼ 10−4). This is still comparable with values typical for electronic or vibrational circular dichroism, and paramagnetic RCD is thus likely to be measurable relatively easily. [ABSTRACT FROM AUTHOR]

A novel chiroptical sensing technique was recently introduced that utilized the helical phase of the structured light as a chiral reagent instead of polarization of light to differentiate enantiopure chiral liquids. The unique advantage of this non-resonant, nonlinear technique is that the chiral signal can be scaled and tuned. In this paper, we extend this technique to enantiopure powders of alanine and camphor by dissolving them in solvents of varying concentrations. We show the differential absorbance of helical light to be an order of magnitude higher relative to conventional resonant linear techniques and is comparable to nonlinear techniques that use circularly polarized light. The origin of helicity dependent absorption is discussed in terms of induced multipole moments in nonlinear light–matter interaction. These results opens up new opportunities in using helical light as a primary chiral reagent in nonlinear spectroscopic techniques. [ABSTRACT FROM AUTHOR]

Circular dichroism (CD) spectra play a crucial role in recognition, separation and detection of chiral molecules. Due to the inherent weak CD response of natural chiral molecules, researchers have endeavored to enhance CD signals through various artificial nanostructures. In this study, combining the advantages of both the dielectric and metal materials, we propose a hybrid dielectric-metal nanostructure consisting of a chiral Si nanorod dimer coupled with a symmetric Au cylinder to achieve robust CD responses. Owing to the plasmon resonance of the Au cylinder, the scattering-CD and absorption-CD of the hybrid system have been enhanced, which result in the enhanced extinction-CD response. Furthermore, the distributions of electric field, magnetic field and displacement current density of both the Si dimer and hybrid nanostructure have been meticulously crafted to elucidate the physical mechanisms underlying amplified CD signals. The synergistic coupling between the magnetic fields of dielectric materials and the electric fields of the Au cylinder leads to an increase in the electric field strength and the asymmetry of near-field distributions. Additionally, spatial overlaps between electric and magnetic fields occur. These factors contribute to the enhanced chiral response of the hybrid system. Meanwhile, the CD signal can be flexibly tuned by adjusting the size of the Au cylinder and Si nanorods. This design offers a versatile approach to enhancing the chiral response of dielectric nanostructures. [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]

Emerging miniaturized optically pumped magnetometers (OPMs) are becoming one of the most desirable approaches for biomagnetic imaging, especially for OPM with elliptically polarized light, which promises single‐light optical pumping and detection with high sensitivity. However, conventional schemes of this kind require a set of bulk polarization optics and tedious adjustment procedures, which compromise the system's compactness and practicality. In this paper, a novel chip‐scale OPM scheme that leverages the monolithic elliptical meta‐polarizer is presented and experimentally demonstrated. The meta‐polarizer with a side length of 3 mm is laid out on a 2 × 2 cm2 glass wafer. It offers the capability to convert arbitrary incident polarization into the desired elliptical polarization and exhibits a tailorable elliptical dichroism (ED) of ≈0.77 at the wavelength of 795 nm. A 4 × 4 × 4 mm3 vapor cell containing 87Rb and N2 is combined with this elliptical meta‐polarizer to construct a miniaturized OPM. The sensitivity of this sensor reaches approximately 13 fT/Hz1/2 in a four‐layer magnetic shield with a dynamic range near zero magnetic field ≈ ±0.55 nT. By exploiting the advantages of planar integrated optics, reduced footprints and scalability are promised. And this work paves the way for the integration of emerging quantum sensors on a chip. [ABSTRACT FROM AUTHOR]

This paper reports on advanced instrumentation for high pressure research developed for the ESRF beamline ID12 which is dedicated to polarization-dependent X-ray absorption spectroscopy at photon energies from 2 to 15 keV. Emphasis is laid on X-ray optics, the design of diamond anvil cell adapted for tender X-ray range and compatible with low temperatures and with high magnetic field as well as a highly efficient X-ray fluorescence detection system. Several examples have been selected to illustrate the performance of the beamline and show what type of advanced spectroscopic techniques can be used to study the local electronic and magnetic properties of materials under pressure. [ABSTRACT FROM AUTHOR]

The optical properties of Microcellular Polyethylene Terephthalate (MCPET) towards light and terahertz waves were compared. Within the measurement range of 0.3–1.3 THz and 30 K to room temperature, the refractive index remained nearly constant at approximately 1.15, close to 1. It was observed that MCPET with a thickness of 0.5 mm transmits over 70% of terahertz waves, while blocking more than 99.9% of light in the 300–2000 nm range. These findings present significant advantages for the design of optical devices using MCPET, highlighting its potential for selective dichroism and high opacity in specific applications. [ABSTRACT FROM AUTHOR]

Chiral metamaterials possess unique optical chiral responses, and the attainment of remarkable intrinsic chirality typically necessitates the disruption of their mirror symmetry to facilitate cross‐coupling between electric and magnetic dipoles. However, achieving such symmetry breaking in a flexible and controllable manner remains challenging due to the limited range of applications afforded by available methodologies. Here, a method is proposed for fabricating robust three‐dimensional (3D) chiral metamaterials by projecting arbitrary planar chiral metasurfaces onto on‐demand height‐tunable 3D silicon structures, thereby effectively modulating their optical chiral responses through continuously tuning the degree of cross‐coupling between dipoles. Experimental and simulation results demonstrate this approach's ability to precisely control circular dichroism (CD) from a non‐chiral state to various activated and enhanced chirality. Enhancing CD with high precision and continuous control manners can naturally provide an advanced opportunity and platform for the future design and actual applications of chiral optical systems. [ABSTRACT FROM AUTHOR]

Understanding the impact of the relativistic motion of a chiral molecule on its optical response is a prime challenge for fundamental science, but it also has a direct practical relevance in our search for extraterrestrial life. To contribute to these significant developments, we describe a multi–scale computational framework that combines quantum chemistry calculations and full–wave optical simulations to predict the chiral optical response from molecules moving at relativistic speeds. Specifically, the effect of a relativistic motion on the transmission circular dichroism (TCD) of three life–essential biomolecules, namely, B–DNA, chlorophyll a, and chlorophyll b, is investigated. Inspired by previous experiments to detect interstellar chiral molecules, we assume that the molecules move between a stationary observer and a light source, and we study the rotationally averaged TCD as a function of the speed of the molecule.We find that the TCD spectrum that contains the signatures of the molecules shifts with increasing speed to shorter wavelengths, with the effects already being visible for moderate velocities. [ABSTRACT FROM AUTHOR]

Time‐dependent density functional theory (TDDFT) simulations are conducted on a series of chiral gold/silver alloy nanowires to explore whether silver doping can produce an enhancement of circular dichroism at the plasmon resonance in these systems, and to identify the quantum‐mechanical origin of the observed effects. We find a strong plasmonic dichroism when one or two helixes of gold atoms are substituted by silver in a linear chiral nanotube, whose pure gold counterpart does not display any plasmonic dichroism, and we rationalize this finding in terms of "decoupling" the destructive interference of excitations in the pure gold nanotube via alloying. However, further attempts to increase the plasmonic dichroism by considering multi‐shell gold nanowires in which one entire shell is doped with silver did not produce the desired effect, but rather a decrease in circular dichroism. We show that this latter result is due to a more severe destructive interference in the dipole excitation contributions, and suggest that further amplification should be possible in principle by properly tuning simultaneously the nanowire structure and chemical ordering. [ABSTRACT FROM AUTHOR]

Plasmonic nanoparticles serve as nonfading pigments for vibrant outdoor glasses and smart windows, offering vivid colors under sunlight with exceptional spatial resolution. However, simultaneously achieving the desired plasmonic coloration in both reflection and transmission with a full‐color gamut remains a formidable challenge, especially when using a single fabrication method. Here, a facile physical triple co‐deposition method to construct scalable plasmonic superstructures, optimal for dichroic color engineering is demonstrated. A key feature of such all‐in‐one plasmonic superstructures lies in extensive color performance in transmission and reflection modes, spanning from transparent invisibility to vivid full colors across the wavelength range of over 600 nm. This exceptional coloration fidelity stems from their 3D‐stacked nanocomposite where plasmonic nanoparticles incorporate a random but uniform distribution within a glass matrix. Wafer‐scale rich and dynamic color images useful for colorful data storage and steganography, as demonstrated through layer‐by‐layer color painting with combinatorial plasmonic superstructures are shown. [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]

Polarization of femtosecond laser radiation influence on the windings of ellipsoidal silver nanoparticles and their orientation in zinc oxide sol-gel films was studied, which caused the appearance of dichroism in the films of the irradiation field. Unlike silver-containing glasses, where this mechanism was discovered, it has hardly been studied in thin sol-gel films before. Femtosecond laser pulses with a high degree of repetition and linear polarization controlled the shape, size and orientation of silver nanoparticles which was oriented horizontally along and across the direction. For dichroism to occur, it is necessary to ensure high-quality separation of laser transducers by Ag nanoparticles and the absence of differences in the zinc oxide matrix. Dichroism in such ZnO:Ag films was investigated by optical microscopy and spectrophotometry away from light. Analysis of the size, content, shape and location of nanoparticles in the film was conducted taking into account electron microscopy. It has been shown that the relationship between dichroism as a result of exposure of the film to laser radiation with energy density ranging from 43 to 99 mJ/cm2 per pulse and flow velocity of 1 mm/s. It was investigated that at given fluence, the interruption of ellipsoidal nanoparticles, most of which are simply oriented along the polarization line of the femtosecond transformation, occurs depending on the direction of the transformation. As a result of laser treatment, modified areas of the film acquired dichroism. When the polarization axis of the incident light was parallel to the direction of linear polarization of the femtosecond radiation with which the regions were recorded, the plasmon resonance peak shifted to the long-wavelength deflection region. When the changed zones were rotated by 90°, the peak of the plasmon resonance shifted to a shorter wavelength region relative to. At fluence above 99 mJ/cm2, dichroism remained, but it decreased sharply, the size of nanoparticles decreased and began to gradually destroy the film matrix with the formation of nanoscale pores and cracks. Obtained results can be used to register polarization-sensitive elements of small sizes, the spectral transmission of which will depend on the orientation of the linear polarization vector of the light incident on them. The proposed method allows adjustment of plasmon resonance peak position in the spectral range from 450 to 650 nm, which can also be used to increase the sensitivity of photodetectors in the specified spectral range.

The interaction between chiral molecules and circularly polarized light is largely influenced by the local optical chirality density. This interaction prompts substantial demand of the design of nanophotonic platforms capable of enhancing such effects across large and accessible volumes. Such a magnification requires nanostructures that provide strong electric and magnetic field enhancements while preserving the phase relation of circular light. Dielectric nanostructures, particularly those able to support resonances, are ideal candidates for this task due to their capacity for high electric and magnetic field enhancements. On the other hand, efficient third harmonic generation requires strong electric field resonances within dielectric materials, a feature often boosted by incorporating plasmonic materials into hybrid systems. In this work, we numerically propose a coupled silicon disk-gold ring system that can exploit the anapole-induced field confinement to provide a broadband magnified circular dichroism under realistic conditions, reaching values up to a 230-fold enhancement. We also demonstrate that this structure can be employed as an efficient third harmonic generator, which, when integrated with chiral media, enables an 800-fold enhancement in circular dichroism. Furthermore, we show that pulsed illumination at intensities up to 10 GW/cm2 does not induce temperature increments that could potentially damage the samples. These findings suggest that this system can be a promising and versatile approach toward ultrasensitive chiral sensing. [ABSTRACT FROM AUTHOR]

This study demonstrates that the magnetic quadrupole (MQ) can make an indispensable contribution to helical dichroism (HD), which is distinct from HD caused by electric quadrupole (EQ). Specifically, the established multipole expansion theory of the light–matter interaction reveals that EQ‐induced HD belongs to the pure electric dipole–quadrupole (E1‐E2) excitation, while newly discovered MQ‐induced HD belongs to the pure magnetic dipole‐quadrupole (M1‐M2) excitation. Metallic propeller meta‐molecules are used to elaborate on this novel physical mechanism and demonstrate that HD can be significantly enhanced and flexibly tuned by increasing stereo twist of propeller meta‐molecules or slightly focusing the linearly polarized vortex beam to improve the orbital angular momentum number. Importantly, the aforementioned intriguing phenomena are validated by fabricating stereo twisted propeller meta‐molecules via nano‐kirigami method. The findings reveal a paradigm‐shift approach to manipulate the chiroptical response of a single metallic nanostructure via photonic orbital angular moment, opening prospects for optical encryption, communication, next‐generation chiroptical spectroscopy, and chiral vortex optical devices. [ABSTRACT FROM AUTHOR]

The rotavirus capsid protein VP6 forms the middle of three protein layers and is responsible for many critical steps in the viral life cycle. VP6 as a structural protein can be used in various applications including as a subunit vaccine component. The head domain of VP6 (VP6H) contains key sequences that allow the protein to trimerize and that represent epitopes that are recognized by human antibodies in the viral particle. The domain is rich in ß-sheet secondary structures. Here, VP6H was solubilised from bacterial inclusion bodies and purified using a single affinity chromatography step. Spectral (far-UV circular dichroism and intrinsic tryptophan fluorescence) analysis revealed that the purified domain had native-like secondary and tertiary structures. The domain could maintain structure up to 44C during thermal denaturation following which structural changes result in an intermediate forming and finally irreversible aggregation and denaturation. The chemical denaturation with urea and guanidinium hydrochloride produces intermediates that represent a loss in the cooperativity. The VP6H domain is stable and can fold to produce its native structure in the absence of the VP6 base domain but cannot be defined as an independent folding unit. [ABSTRACT FROM AUTHOR]

Helical dichroism (HD), which is defined as the difference in optical absorption between chiral pairs of lights involving left-handed (LH) and right-handed (RH) optical vortices (OVs) carrying orbital angular momentum (OAM), is a promising way to characterize chiral materials. In the current major methods of OV generation using spatial light modulators (SLMs), the speed of OAM switching is typically as slow as 100 Hz, which is comparable to low-frequency noise, making precise chiral detection difficult. Here, we theoretically propose and experimentally demonstrate a rapid modulation of the LH and RH OVs at around 50 kHz. This modulation is achieved through a rapid modulation of circularly polarized lights carrying spin angular momentum (SAM), combined with a SAM–OAM conversion technique. We establish a theory not only for rapid OV modulation but also for HD measurements using the modulated OVs. We experimentally verify the theory using helical phase holograms drawn on a SLM as a pseudo-HD active sample. Our work addresses the limitations of current methods and offers a new avenue for precise HD measurements, paving the way for the development of sensitive chiral-optical spectroscopy techniques. [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]

Single-layer transition-metal dichalcogenides provide an unique intrinsic entanglement between the spin/valley/orbital degrees of freedom and the polarization of scattered photons. This scenario gives rise to the well-assessed optical dichroism observed by using both steady and time-resolved probes. In this paper, we provide compact analytical modeling of the onset of a finite Faraday/Kerr optical rotation upon shining with circularly polarized light. We identify different optical features displaying optical rotation at different characteristic energies, and we describe in an analytical framework the time-dependence of their intensities as a consequence of the main spin-conserving and spin-flip processes. [ABSTRACT FROM AUTHOR]

Although more than 10% of the human genome has the potential to fold into non- B DNA, the formation of non-canonical structural motifs as part of long dsDNA chains are usually considered as unfavorable from a thermodynamic point of view. However, recent experiments have confirmed that non-canonical motifs do exist and are non-randomly distributed in genomic DNA. This distribution is highly dependent not only on the DNA sequence but also on various other factors such as environmental conditions, DNA topology and the expression of specific cellular factors in different cell types. In this study, we describe a new strategy used in the preparation of DNA minicircles containing different non-canonical motifs which arise as a result of imperfect base pairing between complementary strands. The approach exploits the fact that imperfections in the pairing of complementary strands thermodynamically weaken the dsDNA structure at the expense of enhancing the formation of non-canonical motifs. In this study, a completely different concept of stable integration of a non-canonical motif into dsDNA is presented. Our approach allows the integration of various types of non-canonical motifs into the dsDNA structure such as hairpin, cruciform, G-quadruplex and i-motif forms but also combinations of these forms. Small DNA minicircles have recently become the subject of considerable interest in both fundamental research and in terms of their potential therapeutic applications. [ABSTRACT FROM AUTHOR]

In this paper, based on a simplified dermis model of cylinder-birefringence, the variation of polarization properties of human skin with its structural parameters was studied. To the best of our knowledge, for the first time, the birefringence parameters of human skin measured by polarization-sensitive optical coherence tomography system was used to analyze the changes of birefringence, dichroism and depolarization with the change of structural parameters. The results of this study are important for interpreting the results of polarization experiments, diagnosing human skin diseases and monitoring the effects of treatment in vivo. [ABSTRACT FROM AUTHOR]

The intermetallic compound Fe 1 − x Co x Si has a helical magnetic order for 0.05 < x < 0.8 , whereas its orbital angular momentum contributing to the occurrence of a Dzyaloshinskii–Moriya interaction has not yet been verified. We applied soft x-ray magnetic circular dichroism spectroscopy on the Fe L 2 , 3 and Co L 2 , 3 edges below T c for Fe 0.75 Co 0.25 Si such that their orbital magnetic moments m orb were evaluated independently. The dichroic signals provide direct experimental evidence that m orb for both Fe and Co is coupled in a parallel manner with each spin counterpart m spin . The ratio of m orb to m spin is independently estimated as m orb / m spin ∼ 3 % for Fe and 9% for Co. By comparing the average of the two m spin values with the saturated magnetization using a commercial superconducting quantum interference device (SQUID) magnetometer, the hole number in the d bands for both Fe and Co is roughly estimated as approximately 1.5. This suggests that Fe and Co should be arranged closely for stabilizing the ferromagnetic moments. [ABSTRACT FROM AUTHOR]

Chiral metamaterials play vital roles in manipulating the circular polarization of electromagnetic waves. Although planar chiral metamaterials are believed to have no true/intrinsic chirality, the design of structural anisotropy can still create enormous circular dichroism, while the mechanism is fully explored. Here, for the first time, it is observed that strong near‐field coupling induces less chiral response in chiral metamaterials. Selective exposure methods to manipulate the near‐field coupling strength, and experimentally validate the circular dichroism difference from tailored near‐field coupling effect are leveraged, which provides strong evidence for the assumption and can be utilized for the structural design framework. Besides, using the enhanced near‐field (over 750‐fold), surface‐enhanced vibrational circular dichroism (SEVCD) for glucose enantiomers, which shows a larger‐than‐one normalized sensitivity compared with metamaterials with chiral response is demonstrated. Furthermore, The potential of SEVCD by detecting a broadband signal using arrayed metamaterials is explored. These findings pave the way toward chiroptical nanophotonic designs for potential biomedical and healthcare applications. [ABSTRACT FROM AUTHOR]

Using a minimallised approach,we designed and synthesized N‐terminal modified peptides W‐KRGNKWLA‐CONH2 (P1) and W‐ARGDGGNGRGA‐CONH2 (P2) using Fmoc‐Chemistry solid phase peptide synthesis protocol. High‐performance liquid chromatograms and mass spectrometry (LCMS and analytical HPLC) were employed to determine the purity and molecular weight of the peptide. Surface tension measurements are used to evaluate peptide surface activity. The primary structure of the peptideis anlaysed by NMR spectroscopy. Circular dichroism studies demonstrate that the secondary structure of the peptide changes minimally when it attached to anionic lipid bilayers (POPC : POPG). According to a steady‐state fluorescence experiment, peptides P1 and P2 preferentially interact with anionic (POPC : POPG) lipid bilayers rather than zwitterionic (POPC) lipid bilayers. The peptide P2 interacts preferentially with anionic lipid membranes and has an anticancer effect due to RGD and NGR binding motifs. The cytotoxicity of the MTT experiment demonstrated that both normal and cancerous cells could lower peptide concentrations below their IC50 levels. Molecular docking also supports in‐vitro anticancer research. Both peptides P1 and P2 were non‐toxic to vero cells and appeared to be more promising as it demonstrated wide spectrum anticancer activity. [ABSTRACT FROM AUTHOR]

Electron magnetic chiral dichroism (EMCD) is a high-resolution technique currently in development for quantitative magnetic measurements using transmitted electrons. However, the inevitable electron damage to materials can be a significant yet easily overlooked factor affecting the quantification accuracy. This work experimentally investigated the electron knock-on damage effects on EMCD of magnetic metals using metallic cobalt as a model. Three issues are involved in the metal-surface damage process. It was revealed that under sustained electron irradiation during spectra acquisition, gradual removal of the thin surface oxidation layer, rather than a simple continuous thickness reduction that changes the diffraction and plural scattering conditions, can lead to notable residual nonmagnetic components in EMCD spectra and may make the quantified result of the orbital-to-spin moment ratio remarkably higher than the actual value. It was, thus, proposed to pay great attention to the surface oxidation and to minimize the effect of the oxidation layer by performing electron irradiation on the target area prior to EMCD experiments. A further experiment was additionally proposed to quantify the impact of thickness reduction on the magnetic components of momentum-resolved electron energy-loss spectra and the EMCD quantification. This study advances the application of EMCD in magnetic metals. [ABSTRACT FROM AUTHOR]

Amorphous solids do not exhibit long-range order due to the disordered arrangement of atoms. They lack translational and rotational symmetry on a macroscopic scale and are therefore isotropic. As a result, differential absorption of polarized light, called dichroism, is not known to exist in amorphous solids. Using helical light beams that carry orbital angular momentum as a probe, we demonstrate that dichroism is intrinsic to both amorphous and crystalline solids. We show that in the nonlinear regime, helical dichroism is responsive to the short-range order and its origin is explained in terms of interband multiphoton assisted tunneling. We also demonstrate that the helical dichroism signal is sensitive to chirality and its strength can be controlled and tuned using a superposition of OAM and Gaussian beams. Our research challenges the conventional knowledge that dichroism does not exist in amorphous solids and enables to manipulate the optical properties of solids. Differential absorption of polarized light, called dichroism, does not exist in amorphous solids due to the disordered arrangements of atoms. Here, the authors demonstrate that dichroism is intrinsic to all solids and can be controlled using helical light beams carrying orbital angular momentum. [ABSTRACT FROM AUTHOR]

A series of uniaxially oriented polyimide (PI) films were fabricated via hot drawing at varying temperatures and draw ratios, and their orientation structure and thermal dimensional stability were investigated in detail. The infrared dichroism based on C = O symmetrical stretching was employed to effectively determine the orientation of chain segments. Other characteristic peaks, such as C = O asymmetric and C-N stretching, were highly sensitive to the geometric structure of chain segments, thereby providing a valuable means for comprehending their morphology. It has been observed that lower thermal expansion coefficient (CTE) can be achieved through low-temperature stretching, while high-temperature stretching is more effective in suppressing thermal shrinkage of the film. By quantitatively analyzing the orientation structure of infrared groups, the minimum structural unit highly associated with CTE was determined. These findings help to deepen our understanding of PI film performance and provide new ideas for studying thermal dimensional stability and draw processing. [ABSTRACT FROM AUTHOR]

Chiral metamaterials exhibit significant circular dichroism (CD) and chiral signal enhancement, which have the potential to be used in novel nano-optical devices. This work describes a bilayer resonant planar chiral metamaterial (PCM) composed of positive and negative Z-shaped gold nanoparticles. It is found that in the near-infrared region, the structure has obvious optical active and chiral near-field enhancement. To explore the origin of chirality, linear superposition method is applied to analyze chiral response intuitively and concisely. What's more, the dependence of the CD spectra on the PCM parameters was thoroughly explored, showing that the CD properties of the proposed PCM arrays strongly depend on the geometric parameters and material type. The bilayer PCM array proposed in this paper not only has a strong chiral signal but also is easy to prepare. More importantly, the spectrum of PCM can be adjusted by simply adjusting the particle rotation angle and changing the material of the dielectric layer, which has broad potential application prospects in the fields of chiral molecular biosensing and asymmetric information transmission. [ABSTRACT FROM AUTHOR]

Nanostructures with chiral features have a wide range of applications in circular polarizers, optical modulators, and optoelectronic devices. In this study, we designed a three-dimensional bilayer T-shaped chiral structure to investigate the circular dichroism of multilayer nanostructures. We simulated the designed chiral structure and results that showed the maximum circular dichroism value occurred when the lower layer T-shaped structure rotated to 40°. The spectral response of the proposed structure can be considered as a coupling between upper and lower resonances, and the mechanism of optical chirality is explored by simulating the internal current distribution in metal. The model revealed that different current oscillations were excited by incident light in the upper and lower layers. Our results provide insightful references for analyzing the physical mechanism of circular dichroism signals and improving the circular dichroism signals of metasurfaces. [ABSTRACT FROM AUTHOR]

The effect of post-growth isothermal annealing in vacuum and in air on the optical properties of Ca3TaGa3Si2O14 crystal samples of Z- and X-cuts is studied. The spectral dependences of the transmission coefficients are measured in the wavelength range (240–700) nm taking into account anisotropy and dichroism. On the Z-cut samples in the initial state an absorption band at λ = 360 nm in the ultraviolet range is observed; in the visible region, there are two absorption bands at λ = 460 nm and λ = 605 nm. Additionally, a band at λ = 290 nm is observed on the X-cut samples. When the sample is rotated around the direction of the light beam by 90 degrees, a change in the intensity of the absorption bands is observed. Annealing in vacuum leads to a decrease in the intensity of the absorption bands in the near ultraviolet and visible range, except for the absorption band at λ = 605 nm. Annealing in air leads to the opposite effect, i.e., an increase in the intensity of the absorption bands, except for the band λ = 605 nm. The value of the anomalous birefringence of the samples was estimated by the Mallard method. The degree of linear dichroism is calculated. It is shown that the degree of dichroism decreases as a result of annealing in vacuum and increases during annealing in air. [ABSTRACT FROM AUTHOR]

In this paper, a bi-layered ultra-thin multifunctional chiral metasurface is proposed to obtain asymmetric transmission (AT), cross-polarization conversion (CPC), and circular dichroism (CD). The multifunctional chiral metasurface realizes an AT with more than 70% efficiency over a Ku-band frequency range from 14.3 to 15.8 GHz, while in the operating frequency band from 13.5 to 16.2 GHz, the CPC ratio is above 90%. In addition, the metasurface exhibits CD in the K-band with a CD parameter of 0.6 at 24 GHz. Furthermore, the functionalities of AT and CPC are stable with changes in the incident angle of up to 60° for both transverse-electric and transverse-magnetic electromagnetic waves. For verification of the anticipated concept, the proposed chiral metasurface is fabricated and measured. The proposed design can be used for potential applications in the Ku- and K-bands for satellite communication and radar. [ABSTRACT FROM AUTHOR]

The advancements in chiroptics have propelled applications beyond traditional optics, expanding its reach into domains such as heat and fluid mechanics. The current research predominantly focused on utilizing plasmonic materials in the photothermal and photofluidic systems. However, these systems face limitations in circular dichroism due to inherent Ohmic loss associated with plasmonic materials. Herein, we introduce the concept of topological polarization singularity in an all-dielectric structure, which supports chiral bound states in the continuum. The introduction of topological polarization singularity gives the structure an impressive chiral light absorption response. The BICs resonant mode achieves a 147-fold field enhancement, significantly improving the photothermal conversion efficiency of dielectric material. Moreover, the g factors of photothermal and optical fluids reach 1.9, approaching the theoretical limit value. Consequently, an exceptionally high degree of circular dichroism is realized in multiple systems including light absorption, photothermal, and photofluidic systems. Our proposed structures can potentially be used in chiral photothermal and chiral nanoparticle capture, as well as photofluidic applications related to biochemistry and clinical biology. [ABSTRACT FROM AUTHOR]

A novel chiroptical spectrophotometer, Multichannel (MC)‐circular dichroism (CD), which does not require a wavelength scan and provides artifact‐free CD spectra in seconds, was developed by solving the incompatibility problem between data acquisition and modulation timescales. The design and instrumentation are compared with the Universal Chiroptical Spectrophotometer (UCS)‐1, which can measure artifact‐free CD spectra in the solid state. Enantiomeric single crystals composed of achiral components, α‐Ni(H2O)6・SO4, and achiral films with substantial macroscopic anisotropies were measured on both MC‐CD and UCS‐1 and compared. [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]

This study aimed to extract collagen‐I from lamb feet (LF) and examine the effects of ultrasound treatment on the structural and molecular characteristics of the collagen. Compared to ultrasonic bath treatment and conventional extraction methods, ultrasonic probe (USP) treatment significantly increased the collagen content of the extract (p < 0.05). The electrophoretic profiles confirmed the presence of α‐ and β‐chains, indicating it as type I. Furthermore, X‐ray diffraction, Fourier‐transform infrared spectroscopy, and circular dichroism spectra analyses revealed that the extraction method did not adversely affect the triple helix structure of the collagen. Moreover, the fibrillar structure of the collagen samples was verified through scanning electron microscopy analyses. Notably, the LF collagen exhibited a high thermal denaturation temperature owing to its elevated imino acid content. The collagen samples exhibited high solubility in acidic pH but low solubility in high salt concentrations. The present findings signified that sonication with USP can effectively enhance the yield of collagen from LF without compromising its quality. Practical Application: This study showed that ultrasonication enhanced the collagen concentration without disturbing the integrity of lamb feet collagen. We expect that lamb feet collagen can be used for industrial processes and consumer products thanks to unique product properties. [ABSTRACT FROM AUTHOR]

In this study, we aimed to investigate the effect of ultrasound (US) combined with different amounts of psyllium husk powder (PHP) (0 %, 0.5 %, 1 %, 2 %, 3 %) on the gelation and structure of goose myofibrillar protein (GMP). The analysis of circular dichroism, surface hydrophobicity and fluorescence spectroscopy showed that the combination of US and 2 % PHP could promote the development of myofibrillar protein (MP) secondary and tertiary structure, which could facilitate the exposure of active site and enhance the interaction between GMP and PHP. Meanwhile, the thermal stability was enhanced with US and PHP treatment. In addition, the analysis of rheology, Low field nuclear magnetic resonance (LF-NMR), Fourier transform infrared (FT-IR) spectroscopy and microstructure showed that US combined with 2 % PHP addition could make the gel network structure denser. Thus, these results suggested that the combination of US and 2 % PHP could promote the unfolding of GMP structure and improve its gel properties. This study provides new insights for the interaction of GMP and PHP under US treatment, improving the application of goose meat in practical production. [Display omitted] • The average particle size of goose myofibrillar protein (GMP) was decreased. • Ultrasound (US) and psyllium husk powder (PHP) improved the thermal stability of GMP. • The free water was converted into immobilized water in US/PHP-2 % group. • US/PHP-2 % gel has more uniform/denser microstructure and better gel properties. [ABSTRACT FROM AUTHOR]

Metamaterials with localized surface plasmon resonances have been the subject of intense research for a wealth of applications ranging from active photonic devices to analytical sensing units that utilizes the local field enhancement to improve sensitivity and decrease acquisition time. Herein, we focus on the modelled properties of a series of spiral metastructures that present multiple chiral plasmon modes in the 1–10 μm mid‐IR spectral range and that could be utilized to enhance vibrational circular dichroism measurements to further identify molecular, supramolecular and structural chirality centres. Finite‐difference time‐domain electromagnetic modelling was conducted to calculate the infrared spectra of the metastructures in response to a circularly polarized excitation. Several geometric parameters were altered to further tune the position of the resonances. In addition, the near‐field distribution of the optical resonances was calculated providing a spatial snapshot of the chiral modes. Preliminary spiral structures were fabricated using electron beam lithography and their vibrational circular response was measured. [ABSTRACT FROM AUTHOR]

Recently, high-throughput quantum cascade laser-based vibrational circular dichroism (QCL-VCD) technology has reduced the measurement time for high-quality vibrational circular dichroism spectra from hours to a few minutes. This study evaluates QCL-VCD for chiral monitoring using flow-through measurement of a changing sample in a circulating loop. A balanced detection QCL-VCD system was applied to the enantiomeric pair R/S-1,1′-bi-2-naphthol in solution. Different mixtures of the two components were used to simulate a racemization process, collecting spectral data at a time resolution of 6 min, and over three concentration levels. The goal of this experimental setup was to evaluate QCL-VCD in terms of both molar and enantiomeric excess (EE) sensitivity at a time resolution relevant to chiral monitoring in chemical processes. Subsequent chemometric evaluation by partial least squares regression revealed a cross-validated prediction accuracy of 2.8% EE with a robust prediction also for the test data set (error = 3.5% EE). In addition, the data set was also treated with the least absolute shrinkage and selection operator (LASSO), which also achieved a robust prediction. Due to the operating principle of LASSO, the obtained coefficients constituted a few discrete spectral frequencies, which represent the most variance. This information can be used in the future for dedicated QCL-based instrument design, gaining a higher time resolution without sacrificing predictive capabilities. Graphical abstract This is a visual representation of the abstract. [ABSTRACT FROM AUTHOR]