Linear Optical Activity Research Articles

Mueller-matrix reconstruction of parameters of phase and amplitude anisotropy in diagnostics of endometriosis and infertility

A new azimuthally stable polarimetric method for processing microscopic images of optically anisotropic structures for different biological layers of histological sections has been proposed. A new model that enables to determine phase anisotropy of biological tissues by using superposition of Mueller matrices of linear birefringence and optical activity has been proposed. The matrix element M44 has been chosen as the main information parameter, which value is independent of rotation angle of both sample and probing beam polarization plane.

Vibrational study, molecular properties and first-order molecular hyperpolarizability of Methyl 2-amino 5-bromobenzoate using DFT method

The molecular structure of Methyl 2-amino 5-bromobenzoate (M2A5B) was investigated by density functional theory employing Becke’s three parameter hybrid exchange functional with Lee–Yang–Parr (B3LYP) co-relational functional involving 6-311++G(d,p) basis set. Harmonic vibrational wavenumber calculation along with the normal mode analysis has been carried out in order to obtain a complete description of molecular dynamics. A detailed interpretation of the Infrared and Raman spectra of M2A5B have been reported. Complete vibrational assignments of the vibrational modes have been done on the basis of the potential energy distribution (PED) in terms of internal coordinates. The scaled vibrational wavenumbers corrected by a recommended set of scaling factors were compared with the experimental results and a fairly good agreement was obtained. The molecular electrostatic potential mapped onto total density surface has been obtained. A study on the electronic properties, such as absorption wavelength, excitation energy and frontier molecular orbitals energy, was performed by time dependent DFT (TD-DFT) approach. Additionally, major contribution from molecular orbitals to the electronic transition was investigated theoretically. The stability of the molecule arising from hyper conjugative interactions and accompanying charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The theoretical 1H and 13C NMR chemical shifts have been calculated by GIAO method and compared with experimentally measured ones. The polarizability and first order hyperpolarizability of the title molecule were calculated and interpreted. The energy gap between frontier orbitals has been used along with electric moments and first order hyperpolarizability, to understand the non linear optical (NLO) activity of the molecule. The prominent vibrational modes contributing to the NLO activity have been identified and examined from the concurrent IR and Raman activity. Thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound at different temperatures have been calculated.

Configuration of singular optical cones in gyrotropic crystals with dichroism

Optical conic singularities in crystals with linear dichroism and natural optical activity at the point of intersection of dispersion curves for the main refractive indices are considered. The possible existence of singularities like a nodal point, tangency point, triple point, and cusps of the first and second order is demonstrated. Forty-nine different types of irreducible fourth-order optical cones obtained by sequential bifurcations of eight main singular cones are established. The classification is based on the concept of roughness of systems depending on parameters.

Synthesis, spectral characterization, single crystal X-ray diffraction and DFT studies of 4-((2,4,5-triphenyl-1H-imidazol-1-yl)methyl)pyridine derivatives

We have synthesized a series of novel 4-((2,4,5-triphenyl-1H-imidazol-1-yl)methyl)pyridine derivatives. The structures of these compounds were confirmed by IR, HR-MS, 1H and 13C NMR spectra. The compound 5g was also confirmed by single crystal XRD. The geometry of the synthesized compounds 5a–5g were examined by density functional theory (DFT) method at B3LYP/6-31G(d,p) level. The optimized geometrical parameters obtained by DFT calculation are in good agreement with single crystal XRD data. The HOMO–LUMO energies describes charge transfer takes place within the molecule. Furthermore, Mulliken and NBO charges were also calculated. The stability and charge delocalization of the molecule were also studied by natural bond orbital (NBO) analysis. Compound 5g exhibited good non linear optical activity and was 20 times greater than that of urea. In addition, molecular electrostatic potential map (MEP) was studied for predicting the reactive sites.

Splitting of cones of optical axes in gyrotropic crystals in the presence of dichroism

Features of the appearance of conical singularities in the presence of linear dichroism and natural optical activity at the point of intersection of dispersion curves of the principal refractive indices of a crystal have been considered. It has been shown that even insignificant dichroism results in the splitting of cones of optical axes into cones of singular optical axes (in a partial case, cones are degenerate into planes) between which a “gap” with identical velocities of proper waves appears. The splitting angle for the AgGaS2 crystal is estimated at about 5°.

Complex degree of mutual anisotropy of linear birefringence and optical activity of biological tissues in diagnostics of prostate cancer

We present theoretical fundamentals of polarization and correlation analysis of the optical anisotropy of biological tissues. Results of measurements of coordinate distributions of the complex degree of mutual anisotropy (CDMA) that are formed by birefringent structures of the prostate tissue with benign and malignant changes are compared. Magnitudes and ranges of variation of statistical (the firstto fourth-order distribution moments) and correlation (excess of autocorrelation functions) parameters of the coordinate CDMA distributions of histological sections of the prostate postoperative bioptic material are studied. Objective criteria of the diagnostics of the appearance of pathology and of the differentiation of the degree of its severity are determined.

Spatial-Frequency Azimuthally Stable Cartography of Biological Polycrystalline Networks

A new azimuthally stable polarimetric technique processing microscopic images of optically anisotropic structures of biological tissues histological sections is proposed. It has been used as a generalized model of phase anisotropy definition of biological tissues by using superposition of Mueller matrices of linear birefringence and optical activity. The matrix elementM44has been chosen as the main information parameter, whose value is independent of the rotation angle of both sample and probing beam polarization plane. For the first time, the technique of concerted spatial-frequency filtration has been used in order to separate the manifestation of linear birefringence and optical activity. Thereupon, the method of azimuthally stable spatial-frequency cartography of biological tissues histological sections has been elaborated. As the analyzing tool, complex statistic, correlation, and fractal analysis of coordinate distributions ofM44element has been performed. The possibility of using the biopsy of the uterine wall tissue in order to differentiate benign (fibromyoma) and malignant (adenocarcinoma) conditions has been estimated.

Numerical solution of Maxwell equations by a finite-difference time-domain method in a medium with frequency and spatial dispersion

We propose an alternative method of integration of Maxwell equations. This method is the generalization of a finite-difference time-domain method with an auxiliary differential equation for the case of a linear optical medium with a frequency dispersion and an arbitrary source of spatial dispersion. We apply this method to the problem of the propagation of short plane-wave linearly polarized light pulses in such a medium. It is shown that some features of their propagation are completely different from those that are generally recognized for the linear optical activity phenomenon. For example, in some cases an initially linearly polarized light pulse becomes elliptically polarized during the propagation. This effect is more prominent in the front part of the pulse.

Pure nonlinear optical activity in metamaterials

We demonstrate a type of meta-atom for creating metamaterials with giant nonlinear optical activity but vanishing linear optical activity in a wide frequency range. Such properties are not found in any natural materials, and we call this regime as pure nonlinear optical activity. We further extend our design concept and show that the metamaterial can be tuned dynamically to exhibit either positive or negative polarization rotation.

Thermotropic poly(azomethine-urethane)s with non linear optical properties: Synthesis and characterization

Two series of the thermotropic main chain poly(azomethine-urethane)s were synthesized by the polyaddition of azadiol, 1,8-octandiol with methylene bis(phenyl isocyanate) (MDI) and tolylene 2,4-diisocyanate (TDI) respectively. The mesomorphic properties and phase transition temperature of the polymers were characterized by differential scanning calorimetry and hot stage polarizing microscopy. These polymers showed nematic messophase. The non linear optical (NLO) activity of the polymers was also investigated.

Theoretical and experimental studies of chiral polyurethanes

The theoretical and experimental design strategies of chiral polyurethanes with good second harmonic generation efficiencies are discussed. The noncentrosymmetry of the polymers was broken by means of chiral and chemical poling. Different varieties of main chain chiral polymers are obtained by varying the composition of chiral and amido diol monomers using DBTDL catalyst. The designed chiral polymer architecture gives rise to high molecular weight polymers by the polyaddition polymerization with good thermal stability, linear and nonlinear optical activity. The polymer with isomannide as chiral moiety and CED (obtained by the aminolysis of e-Caprolactone with 1, 2 diamino ethane) as amido diol monomer is found to possess high second harmonic generation efficiency. Both theoretical and experimental studies based on second order nonlinearity indicated that the designed chiral polyurethanes are useful for various nonlinear optical applications.

Formulation of rigorous coupled-wave theory for gratings in bianisotropic media

A formulation of rigorous coupled-wave theory for diffraction gratings in bianisotropic media that exhibit linear birefringence and/or optical activity is presented. The symmetric constitutive relations for bianisotropic materials are adopted. All of the incident, exiting, and grating materials can be isotropic, uniaxial, or biaxial, with or without optical activity. The principal values of the electric permittivity tensor, the magnetic permeability tensor, and the gyrotropic tensor of the media can take arbitrary values, and the principal axes may be arbitrarily and independently oriented. Procedures for Fourier expansion of Maxwell's equations are described. Distinctive polarization coupling effects due to optical activity are observed in sample calculations.

Chiroptical nature of two-exciton states of light-harvesting complex: Doubly resonant three-wave-mixing spectroscopy

Photosynthetic light-harvesting complex is a coupled multichromophore system. Due to electronic couplings between neighboring chlorophylls in the complex, the one- and two-exciton states are delocalized and they can be written as linear combinations of singly and doubly excited configurations, respectively. Despite that the chiroptical properties of one-exciton states in such a multichromophore system have been investigated by using linear optical activity measurement techniques; those of two-exciton states have not been studied before due to a lack of appropriate measurement methods. Here, we present a theoretical description on chiroptical chi((2)) spectroscopy and show that it can be used to investigate such properties of a photosynthetic light-harvesting system, which is the Fenna-Matthews-Olson complex, consisting of seven bacteriochlorophylls in its protein subunit. To simulate the doubly resonant sum- and difference-frequency-generation spectra of the complex, one- and two-exciton transition dipoles were calculated. Carrying out quantum chemistry calculations of electronically excited states of a model bacteriochlorophyll system and taking into account the dipole-induced dipole electronic transition processes between the ground state and two-exciton states, we could calculate the two-dimensional sum-frequency-generation spectra revealing dominant second-order chiroptical transition pathways and involved one- and two-exciton states. It is believed that the present computational scheme and the theoretically proposed doubly resonant two-dimensional three-wave-mixing spectroscopy would be of use to shed light on the chiroptical natures of two-exciton states of arbitrary coupled multichromophore systems.

Influence of the order of the constituent basis matrices on the Mueller matrix decomposition-derived polarization parameters in complex turbid media such as biological tissues

The influence of the multiplication order of the constituent basis matrices on the Mueller matrix decomposition-derived polarization parameters in complex tissue-like turbid media exhibiting simultaneous scattering and polarization effects are investigated. A polarization sensitive Monte Carlo (MC) simulation model was used to generate Mueller matrices from turbid media exhibiting simultaneous linear birefringence, optical activity and multiple scattering effects. Mueller matrix decomposition was performed with different selected multiplication orders of the constituent basis matrices, which were further analyzed to derive quantitative individual polarization medium properties. The results show that for turbid medium having weak diattenuation (differential attenuation of two orthogonal polarization states), the decomposition-derived polarization parameters are independent of the multiplication order. Importantly, the values for the extracted polarization parameters were found to be in excellent agreement with the controlled inputs, showing self-consistency in inverse decomposition analysis and successful decoupling of the individual polarization effects. These results were corroborated further by selected experimental results from phantoms having optical (scattering and polarization) properties similar to those used in the MC model. Results from tissue polarimetry confirm that the magnitude of diattenuation is generally lower compared to other polarization effects, so that the demonstrated self-consistency of the decomposition formalism with respect to the potential ambiguity of ordering of the constituent matrices should hold in biological applications.

Phase sensitive detection of vibrational optical activity free-induction-decay: vibrational CD and ORD

Optical activity is manifested by chiral molecules including natural products and drugs, so that circular dichroism (CD) and optical rotatory dispersion (ORD) measurements can provide invaluable information on their chiro-optical properties and structures. It is experimentally demonstrated that heterodyne-detected Fourier-transform spectral interferometry with a femtosecond infrared pulse can be used to fully characterize the phase and amplitude of vibrational optical activity free-induction-decay field. The measured spectral interferograms are then converted to the linear optical activity susceptibility whose imaginary and real parts correspond to vibrational CD and ORD spectra. Unlike the conventional differential measurement technique, the present method based on a heterodyned interferometry is shown to be quite robust and stable. We anticipate that the present vibrational optical activity measurement technique will be of critical use in elucidating chiro-optical properties and structural changes in biomolecules.

Quantitative determination of linear and second-harmonic generation optical effective responses of achiral or chiral materials in planar structures: Theory and materials

A theoretical formalism designed to quantify linear optical and second-order nonlinear optical responses of achiral or chiral anisotropic materials in planar structure is presented. In particular, the theory includes linear optical activity that is governed by the gyrotropic components and second-harmonic generation optical rotatory dispersion, the magnitude of which depends on the ratio of chiral and achiral chi((2)) components. Examples are given which reproduce complex interference effects and other subtle optical effects that are encountered in layered structures. Detailed experimental second harmonic generation studies of quartz and dihydrogen phosphate that quantify linear and nonlinear optical activities of these materials are reported.

Mueller matrix decomposition for extraction of individual polarization parameters from complex turbid media exhibiting multiple scattering, optical activity, and linear birefringence

Linear birefringence and optical activity are two common optical polarization effects present in biological tissue, and determination of these properties has useful biomedical applications. However, measurement and unique interpretation of these parameters in tissue is hindered by strong multiple scattering effects and by the fact that these and other polarization effects are often present simultaneously. We have investigated the efficacy of a Mueller matrix decomposition methodology to extract the individual intrinsic polarimetry characteristics (linear retardance delta and optical rotation psi, in particular) from a multiply scattering medium exhibiting simultaneous linear birefringence and optical activity. In the experimental studies, a photoelastic modulation polarimeter was used to record Mueller matrices from polyacrylamide phantoms having strain-induced birefringence, sucrose-induced optical activity, and polystyrene microspheres-induced scattering. Decomposition of the Mueller matrices recorded in the forward detection geometry from these phantoms with controlled polarization properties yielded reasonable estimates for delta and psi parameters. The confounding effects of scattering, the propagation path of multiple scattered photons, and detection geometry on the estimated values for delta and psi were further investigated using polarization-sensitive Monte Carlo simulations. The results show that in the forward detection geometry, the effects of scattering induced linear retardance and diattenuation are weak, and the decomposition of the Mueller matrix can retrieve the intrinsic values for delta and psi with reasonable accuracy. The ability of this approach to extract the individual intrinsic polarimetry characteristics should prove valuable in diagnostic photomedicine, for example, in quantifying the small optical rotations due to the presence of glucose in tissue and for monitoring changes in tissue birefringence as a signature of tissue abnormality.

Polarized light propagation in multiply scattering media exhibiting both linear birefringence and optical activity: Monte Carlo model and experimental methodology

A Monte Carlo model for polarized light propagation in birefringent, optically active, multiply scattering media is developed in an effort to accurately represent the propagation of polarized light in biological tissue. The model employs the Jones N-matrix formalism to combine both linear birefringence and optical activity into a single effect that can be applied to photons as they propagate between scattering events. Polyacrylamide phantoms with strain-induced birefringence, sucrose-induced optical activity, and polystyrene microspheres as scattering particles are used for experimental validation. Measurements are made using a Stokes polarimeter that detects scattered light in different geometries, and compared to the results of Monte Carlo simulations run with similar parameters. The results show close agreement between the experimental measurements and Monte Carlo calculations for phantoms exhibiting turbidity and birefringence, as well as for phantoms exhibiting turbidity, birefringence, and optical activity. Other scattering-independent polarization properties can be incorporated into the developed Jones N-matrix formalism, enabling quantification of the polarization effects via an accurate polarization-sensitive Monte Carlo model.

A Dynamic Coupling Model for Sum Frequency Chiral Response from Liquids Composed of Molecules with a Chiral Side Chain and an Achiral Chromophore

A theoretical formulation for optically active sum frequency generation (OA-SFG) from isotropic chiral solutions was proposed for molecules with a chiral side chain and an intrinsically achiral chromophore. Adapting an electron correlation model first proposed by Höhn and Weigang for linear optical activity, we presented a dynamic coupling model for OA-SFG near the electronic resonance of the achiral chromophore. As a demonstration, we used this model to explain the observed OA-SFG spectra of a series of amino acids near the electronic resonance of the intrinsically achiral carboxyl group. Our model shows that the nonlinear chiroptical response comes about by the through-space correlative electronic interactions between the chiral side chain and the achiral chromophore, and its magnitude is determined by the position and orientation of the bonds that make up the chiral side chain. Using the bond polarizability values in the literature and the conformations of amino acids obtained from calculation, we were able to reproduce the relative OA-SFG strength from a series of amino acids.

Nonlinear optical spectroscopy of chiral molecules

We review nonlinear optical processes that are specific to chiral molecules in solution and on surfaces. In contrast to conventional natural optical activity phenomena, which depend linearly on the electric field strength of the optical field, we discuss how optical processes that are nonlinear (quadratic, cubic, and quartic) functions of the electromagnetic field strength may probe optically active centers and chiral vibrations. We show that nonlinear techniques open entirely new ways of exploring chirality in chemical and biological systems: The cubic processes give rise to nonlinear circular dichroism and nonlinear optical rotation and make it possible to observe dynamic chiral processes at ultrafast time scales. The quadratic second-harmonic and sum-frequency-generation phenomena and the quartic processes may arise entirely in the electric-dipole approximation and do not require the use of circularly polarized light to detect chirality. They provide surface selectivity and their observables can be relatively much larger than in linear optical activity. These processes also give rise to the generation of light at a new color, and in liquids this frequency conversion only occurs if the solution is optically active. We survey recent chiral nonlinear optical experiments and give examples of their application to problems of biophysical interest.