Chiral Media Research Articles

Yield enhancement of elliptical high harmonics driven by bicircular laser pulses

We theoretically investigate the yield enhancement of elliptical high harmonics in the interaction of molecules with bicircular laser pulses by solving the time-dependent Schrödinger equation. It is shown that by adjusting the relative intensity ratio of the two bicircular field components in specific ranges the yield of the molecular high harmonics for the plateau and cutoff regions can be respectively enhanced. To analyze this enhancement phenomenon, we calculate the weights of the electron classical trajectories. Additionally, we also study the ellipticity distribution of harmonics for different intensity ratios. We find that these enhanced harmonics are elliptically polarized, which we mainly attribute to the recombination dipole moment of the major weighted trajectories. These enhanced elliptical extreme ultraviolet and soft x-ray radiations may serve as essential tools for exploring the ultrafast dynamics in magnetic materials and chiral media.

Phase control of pulses distortions through induced circular birefringent chiral atomic medium

Phase control of pulses distortions through induced circular birefringent chiral atomic medium

Anomalous Chiral Transfer: Supramolecular Polymerization in a Chiral Medium of a Mesogenic Molecule.

Here, we report a medium-to-polymer anomalous chiral transfer in the supramolecular polymerization of a tetraphenylporphyrin-based achiral hydrogen-bonding monomer (TPP) in a chiral medium of 5-cyanobiphenyl CB*. A mixture of TPP in (R)-CB* ([TPP]=7.7 mol %) at 40 °C gave a columnar oblique LC mesophase, where the individual columns were composed of an optically active helical supramolecular polymer of TPP as a consequence of a successful medium-to-polymer chiral transfer. Meanwhile, upon dilution of CB* with achiral 5-cyanobiphenyl CB, the optical activity of the system showed an anomalous bell-shaped dependency on the composition of CB*/CB, where the gabs value of 0.049 at CB*/CB=50/50 was 6.0 times larger than the gabs value of CB* alone. Such anomalous chiroptical amplification in CD is most likely due to a change in the stacking geometry of TPP in the oblique columnar LC upon lateral compression.

Topological structures in chiral media: Effects of confined geometry.

We theoretically study orientational structures in chiral magnetics and cholesteric liquid crystal (CLC) nanosystems confined in the slab geometry. Our analysis is based on the model that, in addition to the exchange and the Dzyaloshinskii-Moriya interactions, takes into account the bulk and surface anisotropies. In CLC films, these anisotropies describe the energy of interaction with external magnetic/electric field and the anchoring energy assuming that magnetic/electric anisotropy is negative and the boundary conditions are homeotropic. We have computed the phase diagram and found that the ground state of the film is represented by various delocalized structures depending on the bulk and surface anisotropy parameters, κ^{b} and κ^{s}. These include the z helix and the z cone states, the oblique, and the x helicoids. The minimum energy paths connecting the ground state and metastable helicoids and the energy barriers separating these states are evaluated. We have shown that there is a variety of localized topological structures such as the skyrmion tube, the toron, and the bobber that can be embedded in different ground states including the z cone (conical phase) and tilted fingerprint states. We have also found the structure called the leech that can be viewed as an intermediate state between the toron and the skyrmion tube.

On the direct and inverse electromagnetic scattering by chiral media

Consider the direct and inverse electromagnetic scattering problems by a penetrable cylindrical chiral medium in a homogeneous achiral background medium. The scattering problem can be modeled by a pair of the two-dimensional Helmholtz equations with coupled transmission boundary conditions. The boundary integral equation method is applied to solve the direct scattering problem in a suitable Sobolev space. Then we investigate the linear sampling method for recovering the unknown scatterer from far-field pattern of the scattered field. The coupled boundary conditions bring new challenges during the procedure, and some novel techniques are needed in the theoretical analysis. Finally, we perform several numerical experiments to demonstrate the efficiency and effectiveness of this method.

Tunable control of internet of things information hacking by application of the induced chiral atomic medium

Tunable control of internet of things information hacking by application of the induced chiral atomic medium

Plasma Concept of the Origin of Life under Mete-orite Impact in the Process of Earth Formation and Mass Accumulation

Abstract: An original Plasma Concept of the origin of simplest forms of living matter during the expansion of the plasma forming in the process of a hypervelocity meteorite impact onto the Earth surface is proposed. The concept uses the fact that meteorite bodies were the main contributors to the accumulation of the Earth mass. The feasibility of the concept is confirmed by the results of direct impact experiments and experiments with laser modeling of hypervelocity impact processes involving the generation of plasma identical to impact one. It is shown that during the adiabatic explosive expansion and cooling of the plasma the conditions form that ensure the possibility of stochastic synthesis of simplest and complex molecular structures including those with chirality. Constant unidirectional ring-shaped magnetic field is shown to form in the process of the impact plasma expansion, and that this field interacts with the UV radiation of the plasma to form local physical chiral medium causing moderate breaking of mirror symmetry of enantiomers synthesized in the plasma with the predominant formation of L amino acids and D sugars. At the final stage of this expansion the impact plasma reached both anomalously high catalytic activity and the peak rate of plasma processes, making possible the assembly and ordering of high-molecular structures that could contribute to achieving enantioenrichment or even enantiopurity with the growth of the characteristic size of the plasma region. The earlier proposed protoviroid – a hypothetical virus-like organism – is used as the model of the most primitive living being. The mass of the protoviroid, which consisted of 300 nucleotides and 100 amino acids, did not exceed 100 kDa. The estimates obtained showed that the crust- and meteorite-material plasma processed during the accumulation of the nominal Earth mass could ensure no less than 1047 statistical trials required for the synthesis of a “correct” sequence of a protoviroid monomers. It is also shown conclusively, based on experimental results, that abiogenous processes accompanying the expansion of meteorite plasma and crater formation satisfied all the requirements needed to ensure the emergence of a protoviroid and formation of a medium allowing the survival of the first living being in the geological history of the Earth. Keywords: life origin; meteorite impact; plasma; breaking mirror symmetry; homochirality; enantiopurity; stochastic synthesis; statistical sampling

Surface sum-frequency generation from chiral medium by elliptically polarized light beyond plane-wave approximation and coplanar geometry of incidence

Aiming to study the nonlinear response of the surface of isotropic chiral medium, we obtained analytical expression relating the transverse amplitudes of the spatial Fourier-spectra of two incident arbitrary polarized fundamental beams and one signal reflected beam at the sum-frequency within the first-order approximation by their divergence angles. The calculations, carried out in paraxial approximation, simultaneously take into account the spatial dispersion of the bulk of the medium, its near-surface heterogeneity and the transverse finiteness of the three interacting light beams with arbitrary amplitude profiles and orientation in space. A special compact form for the final formulas was found, which makes use of effective nonlinear transformation tensors, the components of which are solely determined by the geometry of incidence of the beams and the material constants of the medium. A possibility of ‘switching off’ the certain mechanisms of nonlinear response by choosing the specific polarization states of the incident beams is discussed.

Plasmonic characteristics of the structure with double graphene layers immersed in chiral media and applications in detection of chirality.

The propagating behavior of surface plasmons in chiral media is different from that in achiral media. By comparing the propagation behavior of SPPs, the chirality of the environment can be evaluated. We theoretically reveal the features of SPPs in a structure with two individual graphene sheets surrounded by chiral environment. A more universal dispersion relation covering the achiral cases is obtained. The effects of the chirality of medium and the chemical potential of graphene on the SPPs are explored. Besides, a novel method of detecting the chirality of the environment based on the lateral optical force and torque is proposed. The characteristics of the structure may enrich the surface plasmonic wave theory on the waveguides with multiple graphene sheets and provide new opportunities for the design of more compact nanophotonic functional devices and novel biosensors.

Path integral study of the Casimir effect in a chiral medium

The Casimir effect is a remarkable macroscopic feature of QED, while recent lattice studies have also shown its potential nontrivial consequences in QCD. In light of having a better understanding of the Casimir effect, it is advantageous to have a self-contained path integral formulation of the phenomenon. I will show how the Casimir effect between two uncharged plates in the presence of a chiral medium, modeled with an axion term θF͂μvFμv, can be formulated in terms of the path integral, and how such a formulation leads to a 3D effective action of the restricted electromagnetic field.

Scattering Relations for Two-Dimensional Electromagnetic Waves in Chiral Media

We consider the scattering of time-harmonic plane waves by an infinitely long penetrable chiral cylinder. The electromagnetic scattering problem is reduced to a transmission problem for a system of two-dimensional Helmholtz equations. We prove the classical reciprocity principle, a general scattering theorem and an optical theorem in R2. Using Herglotz wave functions we define the corresponding far field operator. Applying the general scattering theorem useful relations are proved for the reconstruction of the scatterer. We also prove that for real chirality measure of the penetrable scatterer the far field operator has a countable number of eigenvalues which lie on a circle.

Poly(arylisocyanides) as Versatile, Enantiodiscriminating Alignment Media for Small Molecules.

Lyotropic liquid crystalline (LLC) phases of amino acid derived polyarylisocyanides were employed as chiral alignment media for the measurement of residual dipolar couplings (RDCs) of small chiral organic molecules. Anisotropic samples in CDCl3 displayed quadrupolar splittings of the deuterium signal in the range of several hundreds of Hertz. The LLC phases showed excellent orienting properties for a broad range of analytes bearing various functional groups. The precise extraction of RDCs in the range of up to ±40 Hertz from F2-coupled HSQC spectra was possible. Additionally, the chiral environment offers the opportunity for diastereomorphous interactions with the enantiomers of chiral analytes leading to two different sets of RDCs. This differential order effect was particularly pronounced with ketones and alcohols.

Deep Eutectic Solvents Formed by (+)-Dtta and L-Menthol as Novel Chiral Recognition and Separation Media for Enantioselective Extraction of Valsartan Enantiomers

Deep Eutectic Solvents Formed by (+)-Dtta and L-Menthol as Novel Chiral Recognition and Separation Media for Enantioselective Extraction of Valsartan Enantiomers

Transfer matrix method for light propagation in variable complex chiral media.

By taking a cholesteric liquid crystal (CLC) as an example and treating it as a multilayer stack of birefringent plates, we use a transfer matrix method to analyze light propagation in a common chiral medium in consideration of interlayer reflection and transmission. Based on the transfer matrix, the electric field distribution can be expressed in the form of linearly as well as circularly polarized components, so as to discuss the change of the polarization state of light in the transmission process. The transfer matrix of the same medium with different chirality can be converted by only changing the rotation matrix in the calculation process. Electric field distributions, band structure, transmission, and reflection spectra are calculated when circularly polarized light is incident normally on CLCs or on composite periodic structures of left- and right-handed CLCs. The results obtained by using this transfer matrix method are in good agreement with those obtained by the method based on solving the eigenvalues of Maxwell's equations. Finally, the transfer matrix method is used to calculate the dynamic transmission properties of CLCs under external magnetic field, which is of great significance for the research of noncontact controllable optical devices. The presented computational method saves computing time and can be used for constructing new photonic microstructures with different chiral media.

Tailoring Optical Vortical Dichroism with Stereometamaterials

AbstractChiroptical response, investigating the interaction between photonic angular momenta and chiral media, is widely applied in optics and material science. In photonic spin angular momentum (SAM) dimension, tailoring circular dichroism (CD) is realized by varying chiral metamaterials for compact circular polarizers and enantiomer sensing. However, in photonic orbital angular momentum (OAM) dimension, tailorable chiroptical property by artificial metamaterials at a fixed operating wavelength remains elusive. Here, it is proposed and demonstrated that twisted stereometamaterials can yield OAM‐dependent tailorable vortical dichroism (VD) ranging from −97% to +98%. Engineering the geometrical parameters and symmetry of the twisted stereometamaterials can flexibly control the spectral characteristics of VD measurements such as sign, magnitude, and position. The twisted stereometamaterials, managing the transmission behaviors of light with various OAM, holds great promise for developing miniaturized components in integrated photonics and chiroptical spectroscopy.

Advanced chiral molecular media for enantioselective electrochemistry and electroanalysis

An increasing number of strategies and tools have been proposed to endow the electrochemical interphase with chirality, to achieve enantiodiscrimination in analytical and/or preparative applications. So far, chirality has mostly been implemented not only at the electrode surface side but also on the medium one. Recently, the attractiveness of the latter approach has remarkably increased on account of the increasing availability of advanced chiral molecular media with intrinsic attractive features for electrochemistry applications, such as chiral ionic liquids, chiral ionic liquid crystals, and chiral deep eutectic solvents. With respect to solid layer/fixed chiral networks, advanced chiral media can still offer a reasonably high degree of local structuring, while being less demanding concerning preparation and management protocols, as well as less sensitive to fouling/regeneration issues. Different ways to implement chirality in advanced molecular media, including cases of powerful ‘inherent chirality,’ will be presented and discussed, particularly focusing on recent applications in the electrochemical field.

Efficient preparation of stereopure amphiphilic 1,2-amino alcohols by using preparative enantioselective HPLC.

Chiral amphiphiles are useful for controlling the structures and properties of supramolecular assemblies, but their stereocontrolled synthesis is generally difficult, because their long alkyl chains tend to bring unfavorable effects on the solubility, reactivity, and crystallinity of molecules. Typical examples are amphiphilic 1,2-amino alcohols (S)-1 and (1S,2S)-2 developed by our group, which were known to serve as chiral reaction media for controlling the stereochemistry of asymmetric photoreactions. We previously developed synthetic schemes for these 1,2-amino alcohols, but their synthetic efficiencies were unsatisfactory (13 steps with 2% overall yield for (S)-1; eight steps with 8% yield for (1S,2S)-2). As the main reason of such low efficiencies, the stereocontrolling methods we previously employed (diastereomer-salt crystallization for (S)-1; stereoselective reactions for (1S,2S)-2) were not ideal. Here, we report highly improved synthetic schemes for (S)-1 and (1S,2S)-2 based on the enantioselective high performance liquid chromatography (HPLC) separation of intermediates in preparative scales. Compared with the previous schemes, the new schemes are advantageous in fewer number of steps, higher overall yield, and lower risk of racemization (seven steps with 15% overall yield for (S)-1; seven steps with 26% overall yield for (1S,2S)-2).

Detecting Antibody–Antigen Interactions with Chiral Plasmons: Factors Influencing Chiral Plasmonic Sensing

Chiral near fields possessing enhanced asymmetry (superchirality), created by the interaction of light with (chiral) nanostructures, potentially provide a route to novel sensing and metrology technologies for biophysical applications. However, the mechanisms by which these near fields lead to the detection of chiral media is still poorly understood. Using a combination of numerical modeling and experimental measurements on an antibody–antigen exemplar system, important factors that influence the efficacy of chiral sensing are illustrated. It is demonstrated that localized and lattice chiral resonances display enantiomeric sensitivity. However, only the localized resonances show a strong dependency on the structure of the chiral media detected. This can be attributed to the ability of birefringent chiral layers to strongly modify the properties of near fields by acting as a sink/source of optical chirality, and hence alter inductive coupling between nanostructure elements. In addition, it is highlighted that surface morphology/defects may amplify sensing capabilities of localized chiral plasmonic modes by mediating inductive coupling.

Analogous Optical Activity in Free Space Using a Single Pancharatnam–Berry Phase Element

AbstractIt is commonly believed that optical activity (OA) is manifested mainly in chiral media, but rare in non‐chiral structures. Here, an analog of OA in free space is experimentally demonstrated by using a single liquid‐crystal Pancharatnam–Berry phase element (PBPE), for which the mechanism is highly consistent with that of the traditional OA. The specifically designed PBPE supports the direction‐dependent polarization rotation of a Bessel beam with controllable “rotatory power.” Such a polarization rotation can be revoked by another PBPE with the same structure. Unlike in a chiral medium, this scheme shows simultaneous realization of equivalent leverotation and dextorotation merely by switching the optical element orientation, promising for applications non‐magnetic optical devices such as optical isolators.

Anomalous Hall instability in the Chern-Simons magnetohydrodynamics

The Chern-Simons magnetohydrodynamics (CSMHD) is introduced using a Maxwell-Chern-Simons (MCS) Lagrangian including an axion-like field $\Theta$. The MCS equation of motion derived from this Lagrangian consists of a modified current, including a chiral magnetic (CM) and an anomalous Hall (AH) current, in addition to the ordinary Ohm current of resistive magnetohydrodynamics (MHD). The former consists of an axial chemical potential, which is given in terms of the temporal comoving derivative of $\Theta$, and the latter arises from the spatial gradient of $\Theta$. As it turns out, the existence of the axial chemical potential is a nonequilibrium effect that plays no role in the linear stability analysis, whereas the AH current arises as in the first-order linear perturbation of the thermal equilibrium. We analyze the linear stability and causality of the CSMHD in a resistive and chiral medium. We show that the Alfven modes propagating sufficiently close to the direction of the magnetic field are unstable but causal. They are also accompanied by a genuine nonhydro mode. A stable mode in a particular direction can correspond to an unstable mode propagating in the exact opposite direction. The AH instability is a manifestation of a breakdown of the parity. A numerical analysis of the phase velocity confirms these results.