Dichroism Parameters Research Articles

DIFFERENTIAL MUELLER-MATRIX MAPPING OF THE POLYCRYSTALLINE COMPONENT OF BIOLOGICAL TISSUES OF HUMAN ORGANS

The article presents the materials of diagnostic application of the method of differential Mueller-matrix mapping of optically anisotropic architectonics of the layers of soft matter of the female reproductive sphere – histological sections of uterine biopsy. The efficiency and accuracy of differential diagnostics of benign and precancerous conditions of endometrial tissue are considered using statistical analysis of algorithmically reproduced maps of average values of linear and circular birefringence and dichroism parameters of optically anisotropic architectonics of representative samples of native histological sections of the uterine wall. The values of the balanced accuracy of differential diagnostics are presented by using the technique of statistical analysis of coordinate distributions of the mean values of the optical anisotropy parameters.

Multi-functional device: manipulating linear and circular-polarization conversion in a terahertz chiral metamaterial.

We propose a terahertz chiral metamaterial as a multi-functional device to manipulate asymmetry transmission of linear polarized waves, linear-to-elliptical polarization conversion and circular dichroism in transmission mode while asymmetry reflection of circular polarized waves. For incidence of linear polarized waves, dual-band asymmetry transmission is shown around 0.42 THz and 1.04 THz where asymmetry transmission factors reach up to two peak values: ∼0.51 and ∼0.55, respectively. Intense linear-to-elliptical polarization conversion occurs at 0.81 THz and 0.97 THz, respectively. For incidence of circular polarized waves, a strong circular dichroism appears at 0.36 THz where circular dichroism parameter reaches to ∼0.64 and asymmetry reflection is displayed around 0.36 THz with the maximum of asymmetry reflection factors approaching to 0.55.

Characterization of collagen response to bone fracture healing using polarization-SHG

In this study, we extend on the three parameter analysis approach of utilizing a noninvasive dual-liquid–crystal-based polarization-resolved second harmonic generation (SHG) microscopy to facilitate the quantitative characterization of collagen types I and II in fracture healing tissues. The SHG images under various linear and circular polarization states are analyzed and quantified in terms of the peptide pitch angle (PA), SHG-circular dichroism (CD), and anisotropy parameter (AP). The results show that the collagen PA has a value of 49.26° after 2 weeks of fracture healing (collagen type II domination) and 49.05° after 4 weeks (collagen type I domination). Moreover, the SHG-CD and AP values of the different collagen types differ by 0.05. The change tendencies of the extracted PA, SHG-CD, and AP parameters over the healing time are consistent with the collagen properties of healthy nonfractured bone. Thus, the feasibility of the proposed dual-liquid–crystal-based polarization-SHG method for differentiating between collagen types I and II in bone fracture healing tissue is confirmed.

A giantly chirality tunable terahertz metasurface based on 3D folded structure with vanadium dioxide

Compared with ordinary chiral materials, chiral metamaterials possess giant chiral optical response, which have been widely used in many optical applications, such as circular polarizers, chiral light imaging and asymmetric transmission. Here, a tunable 3D folded metasurface based on vanadium dioxide (VO2) is proposed to achieve giant chiral optical effect in the terahertz band. The 3D folded metasurface comprises of two folded antisymmetric rectangular split rings resonators (SRRs). By folding the SRRs at a certain angle, the mirror symmetric structure was broken. The results shows that the circular dichroism (CD) parameter reaches a maximum of 0.83 at the folding angle of 45° and the spin-selective transmission is up to 0.89. The designed 3D folded metasurface can operate in a wide incident angle range of 0–55°. What’s more, by adjusting the conductivity of VO2, the dynamic tuning of CD can be realized, achieving the switch between the “ON” and “OFF” states. The proposed 3D folded metasurfaces provides an approach to realize the giant CD, which shows potential application in many fields, such as chiral sensing, polarization control, spin optical communication, and optical imaging.

Visible-Light-Prompted Synthesis and Binding Studies of 5,6-Dihydroimidazo[2,1-b]thiazoles with BSA and DNA Using Biophysical and Computational Methods.

Fused heterocyclic systems containing a bridgehead nitrogen atom have emerged as imperative pharmacophores in the design and development of new drugs. Among these heterocyclic moieties, the imidazothiazole scaffold has long been used in medicinal chemistry for the treatment of various diseases. In this study, we have established a simplistic and environmentally safe regioselective protocol for the synthesis of 5,6-dihydroimidazo[2,1-b]thiazole derivatives from easily available reactants. The reaction proceeds through in situ formation of the α-bromodiketones ensuing trap with imidazolidine-2-thione to provide these versatile bicyclic heterocycles in excellent yields. The synthesized compounds were screened through the molecular docking approach for the most stable complex formation with bovine serum albumin (BSA) and calf thymus deoxyribonucleic acid (ctDNA). The selected compound was further studied using ex vivo binding studies, which revealed moderate interactions with BSA and ctDNA. The binding studies were performed using biophysical approaches including UV-visible spectroscopy, steady-state fluorescence, circular dichroism (CD), and viscosity parameters.

Parity‐Violation Studies with Partially Stripped Ions

AbstractA theoretical study of photoexcitation of highly charged ions from their ground states, a process which can be realized at the Gamma Factory at CERN, is presented. Special attention is paid to the question of how the excitation rates are affected by the mixing of opposite‐parity ionic levels, which is induced both by an external electric field and the weak interaction between electrons and the nucleus. In order to reinvestigate this “Stark‐plus‐weak‐interaction” mixing, well‐known in neutral atomic systems, we employ relativistic Dirac theory. Based on the developed approach, detailed calculations are performed for the 1s 2s1/2and (M1 + parity–violating–E1) transitions in hydrogen‐ and lithium‐like ions, respectively. In particular, we focus on the difference between the excitation rates obtained for the right‐ and left‐circularly polarized incident light. This difference arises due to the parity violating mixing of ionic levels and is usually characterized in terms of thecircular–dichroismparameter. We argue that future measurements of circular dichroism, performed with highly charged ions in the SPS or LHC rings, may provide valuable information on the electron–nucleus weak–interaction coupling.

Elliptic dichroism in strong-field ionization of atoms subjected to tailored laser fields.

The differential ionization rate for strong-field ionization by tailored laser fields of atomic systems averaged over the magnetic quantum number satisfies particular inversion and reflection symmetries. The symmetries of the elliptic-dichroism parameter, which is related to the change of sign of the ellipticity of the laser field, are considered in detail, with particular emphasis on high-order above-threshold ionization. The general results are illustrated by the examples of an elliptically polarized laser field and a bi-elliptical orthogonally polarized two-color (BEOTC) field. For the BEOTC field the differential ionization rate and the elliptic-dichroism parameter are investigated for the ω-2ω and ω-3ω field combinations and for various relative phases between the laser-field components. The inversion and reflection symmetries of the photoelectron momentum distribution in the polarization plane of the field depend on the parities of r and s in the rω--sω BEOTC field combination and on the relative phase between the field components. We suggest that, by analyzing the symmetry properties of the measured momentum distribution of the elliptic-dichroism parameter, one can identify the mechanism of strong-field ionization. If the rescattering mechanism is dominant one can use these distributions to obtain information about the atomic and molecular structure and dynamics.

Skin carcinogenesis in mice using UVB radiation

Ultraviolet B (UVB) radiation is directly related to sunburn and other visible changes on the skin surface, including discoloration and skin carcinoma. This study investigates the influence of UVB rays (wavelength from 290-320nm) on the formation of cancerous tissues and also shows the differences between abnormal and normal tissue. The mice were stimulated with DMBA chemical protocol and exposure to UVB radiation for skin carcinogenesis. Normal and cancerous skin tissue were stained with Hematoxylin and Eosin, then were measured to obtain optical properties by applying Mueller-Matrix Decomposition, which is considered as an effective skin structure analysis method. Long term exposure to UVB radiation caused skin inflammation and the appearance of crystal bumps. Histopathology results clearly indicate the increasing number of papilloma cells, and prolonged damage by UVB radiation. Skin structural analysis was specified with the optical parameters by Mueller Matrix Decomposition method. The extension of skin carcinoma significantly lessened the values of Linear Birefringence (LB) and Circular Birefringence (CB), as well as the variation of Linear Dichroism (LD) and Circular Dichroism (CD) parameters help validate the differences between normal and squamous cell skin sample.

3D Mueller Matrix Reconstruction of the Optical Anisotropy Parameters of Myocardial Histopathology Tissue Samples

Diseases affecting myocardial tissues are currently a leading cause of death in developed nations. Fast and reliable techniques for analysing and understanding how tissues are affected by disease and respond to treatment are fundamental to combating the effects of heart disease. A 3D Mueller matrix method that reconstructs the linear and circular birefringence and dichroism parameters has been developed to image the biological structures in myocardial tissues. The required optical data is gathered using a Stokes polarimeter and then processed mathematically to recover the individual optical anisotropy parameters, expanding on existing 2D Mueller matrix implementations by combining with a digital holography approach. Changes in the different optical anisotropy parameters are rationalised with reference to the general tissue structure, such that the structures can be identified from the anisotropy distributions. The first to fourth order statistical moments characterising the distribution of the parameters of the optical anisotropy of the polycrystalline structure of the partially depolarising layer of tissues in different phase sections of their volumes are investigated and analysed. The third and fourth order statistical moments are found to be the most sensitive to changes in the phase and amplitude anisotropy. The possibility of forensic medical differentiation of death in cases of acute coronary insufficiency (ACI) and coronary heart disease (CHD) is considered as a diagnostic application. The optimal phase plane (θ∗=0.7rad) has been found, in which excellent differentiation accuracy is achieved ACI and CHD -Ac(ΔZ4(θ∗,ΦL,ΔL))=93.05%÷95.8%. A comparative analysis of the accuracy of the Mueller-matrix reconstruction of the parameters of the optical anisotropy of the myocardium in different phase planes (θ=0.9radandθ=1.2rad), as well as the 2D Mueller-matrix reconstruction method was carried out. This work demonstrates that a 3D Mueller matrix method can be used to effectively analyse the optical anisotropy parameters of myocardial tissues with potential for definitive diagnostics in forensic medicine.

Im{χ(3)} spectra of 110-cut GaAs, GaP, and Si near the two-photon absorption band edge

Spectra of the degenerate two-photon absorption coefficient β(ω), anisotropy parameter σ(ω), and dichroism parameter δ(ω)=[σ(ω)+2η(ω)]/2 of crystalline 110-cut GaAs, GaP, and Si, at 300 K were measured using femtosecond pump–probe modulation spectroscopy over an excitation range in the vicinity of each material’s half-bandgap Eg/2 (overall 0.62<ℏω<1.91 eV or 2000>λ>650 nm). Together, these three parameters completely characterize the three independent components of the imaginary part of the degenerate third-order nonlinear optical susceptibility tensor Im{χabcd(3)(ω)}. In direct-gap GaAs, these components peak at ℏω≈0.78Eg, which is close to the peak at ℏω=0.71Eg predicted by the Jones–Reiss phenomenological model. The dispersion is comparable with ab initio calculations. In indirect-gap GaP and Si, these components tend to increase with ℏω over our tuning range. In Si, the dispersion differs significantly from predictions of semi-empirical models, and ab initio calculations do not account for transitions below the two-photon direct bandgap, motivating further investigation. Kleinman symmetry was observed to be broken in all three materials. We also note anomalies observed and their possible origins, emphasizing the advantages of a 2-beam experiment in identifying the contribution of various nonlinear effects.

Coupling effects among elementary polarization properties

In this work, we propose that there exist coupling effects among birefringence, dichroism and off-diagonal depolarization parameters of differential Mueller matrix of random anisotropic media. An anisotropic spatial correlation function of anisotropic random medium is proposed to explain this phenomenon. The consequences of these effects are then pointed out. The idea in this work is very helpful for accurate interpretation of the measured Mueller matrices of optically anisotropic depolarizing medium. In addition, the concept of the anisotropic spatial correlation function of anisotropic random medium will open a new door and will play a central role for analyzing polarized light scattering by anisotropic random media.

Ghost polarimetry with unpolarized pseudo-thermal light.

We present an experimental implementation of the ghost polarimetry concept in unpolarized light, which allows obtaining complete information on the spatial distribution of polarization properties of objects with linear dichroism. It is theoretically shown that it is possible to restore the spatial distribution of the azimuth and a value of anisotropy of such objects. The developed technique allows us to free up the object arm from all additional optical elements, including polarizers. The experimental results of measuring the dichroism parameters of a test four-sectional sample are presented, which demonstrate the efficiency of the method and confirm the correctness of the developed theoretical model.

Differential Mueller matrix imaging of partially depolarizing optically anisotropic biological tissues

Since recently, a number of innovative polarization-based optical imaging modalities have been introduced and extensively used in various biomedical applications, with an ultimate aim to attain the practical tool for the optical biopsy and functional characterization of biological tissues. The techniques utilize polarization properties of light and Mueller matrix mapping of microscopic images of histological sections of biological tissues or polycrystalline films of biological fluids. The main drawback of currently developed laser polarimetry approaches and Mueller matrix mapping techniques is poor reproducibility of experimental data. This is due to azimuthal dependence of polarization and ellipticity values of most matrix elements to sample orientation in respect to incidence light polarization. Current study aims to generalize the methods of laser polarimetry for diagnosis of partially depolarizing optically anisotropic biological tissues. A method of differential Mueller matrix mapping for reconstruction of linear and circular birefringence and dichroism parameter distributions of partially depolarizing layers of biological tissues of different morphological structure is introduced and practically implemented. The coordinate distributions of the value of the first-order differential matrix elements of histological sections of brain tissue with spatially structured, optically anisotropic fibrillar network, as well as of parenchymatous tissue of the rectum wall with an “islet” polycrystalline structure are determined. Within the statistical analysis of polarization reproduced distributions of the averaged parameters of phase and amplitude anisotropy, the significant sensitivity of the statistical moments of the third and fourth orders to changes in the polycrystalline structure of partially depolarizing layers of biological tissue is observed. The differentiation of female reproductive sphere connective tissue is realized with excellent accuracy. The differential Mueller matrix mapping method for reconstruction of distributions of linear and circular birefringence and dichroism parameters of partially depolarizing layers of biological tissues of different morphological structures is proposed and substantiated. Differential diagnostics of changes in the phase (good balanced accuracy) and amplitude (excellent balanced accuracy) of the anisotropy of the partially depolarizing layers of the vagina wall tissue with prolapse of the genitals is realized. The maximum diagnostic efficiency of the first-order differential matrix method was demonstrated in comparison with the traditional methods of polarization and Mueller matrix mapping of histological sections of light-scattering biological tissues.

Phenomenological model for mixed multiphoton absorption in bialkali photocathode and application to ultrafast pulse characterization

We propose a phenomenological model composed of concise formulas to describe mixed multiphoton absorption (MPA), revealing its quasi-exponent-function in relation to intensity, complicated spectral features, and polarization dependence, and then demonstrate it perfectly by experiments on a bialkali-cathode photomultiplier-tube (PMT) single-photon detector. The dichroism parameter is obtained based on polarization dependent visibility. Accomplishing MPA-based autocorrelation, we manifest that the peak-to-baseline contrast ratio is determined by the mixture exponent. After extracting the pure two-photon absorption, we obtain the ultrafast pulse width which agrees well with that of the standard autocorrelator. Furthermore, we put forward the mutual-correlation scheme and acquire accurately the time jitter of a femtosecond-pulse train. Our results pave the way for analyzing high-order complex MPAs and characterization of ultrafast pulses with super accuracy by a widely used bialkali PMT.

Application of two-dimensional intensity maps in high-accuracy polarimetry.

We propose the analysis of 2D intensity contour maps which is based on the optical transmission function for the polarizer-specimen-analyzer system. A small modification of the high-accuracy universal polarimeter (HAUP) technique was used to measure the intensity maps (HAUP maps) and determine the phase retardation, linear dichroism (LD) parameters, and multiple light reflection contribution in uniaxial crystals. We have performed measurements in a direction perpendicular to the optical axis on pure birefringent LiNbO3, birefringent optically active SiO2, and two birefringent optically active dichroic galogermanate crystals doped with Mn3+ and Cr3+ ions. We have obtained good agreement of the experimental data for 532, 633, and 650nm wavelengths with analytical values. These results extend the capabilities of high-accuracy polarimetry to anisotropic crystal studies.

Modeling Electronic Circular Dichroism within the Polarizable Embedding Approach.

We present a systematic investigation of the key components needed to model single chromophore electronic circular dichroism (ECD) within the polarizable embedding (PE) approach. By relying on accurate forms of the embedding potential, where especially the inclusion of local field effects are in focus, we show that qualitative agreement between rotatory strength parameters calculated by full quantum mechanical calculations and the more efficient embedding calculations can be obtained. An important aspect in the computation of reliable absorption parameters is the need for conformational sampling. We show that a significant number of snapshots are needed to avoid artifacts in the calculated electronic circular dichroism parameters due to insufficient configurational sampling, thus highlighting the efficiency of the PE model.

Ratio of ellipticities between 192 and 208 nm (R1 ): An effective electronic circular dichroism parameter for characterization of the helical components of proteins and peptides.

Circular dichroism (CD) spectroscopy represents an important tool for characterization of the peptide and protein secondary structures that mainly arise from the conformational disposition of the peptide backbone in solution. In 1991 Manning and Woody proposed that, in addition to the signal intensity, the ratio between [θ]nπ* and [θ]ππ*ǁ ((R2 ) ≅ [θ]222 /[θ]208 ), along with [θ]ππ*⊥ and [θ]ππ*ǁ ((R1 ) ≅ [θ]192 /[θ]208 ), may be utilized towards identifying the peptide/protein conformation (especially 310 - and α-helices). However, till date the use of the ratiometric ellipticity component for helical structure analysis of peptides and proteins has not been reported. We studied a series of temperature dependent CD spectra of a thermally stable, model helical peptide and its related analogs in water as a function of added 2,2,2-trifluoroethanol (TFE) in order to explore their landscape of helicity. For the first time, we have experimentally shown here that the R1 parameter can characterize better the individual helices, while the other parameter R2 and the signal intensity do not always converge. We emphasize the use of the R1 ratio of ellipticities for helical characterization because of the common origin of these two bands (exciton splitting of the amide π→ π* transition in a helical polypeptide). This approach may become worthwhile and timely with the increasing accessibility of CD synchrotron sources.

Parent, Unsubstituted Hemiporphycene: Synthesis and Properties.

Among seven possible nitrogen-in constitutional isomers of porphyrin only one, porphycene, has been obtained so far in the free, unsubstituted form. Herein, the synthesis of another isomer, parent hemiporphycene (HPc), and its thorough structural, spectral, photophysical, electrochemical, and theoretical characterization are reported. Most of the properties of HPc are intermediate between those of porphyrin and porphycene, as evidenced by the values of inner-cavity dimensions, orbital-energy splittings, absorption coefficients, magnetic circular dichroism parameters, NH-stretching frequencies, fluorescence quantum yields, tautomerization rates, and redox potentials. The largest differences arise with respect to tautomerism, due to the low symmetry of HPc and inequivalence of the four nitrogen atoms that define the inner cavity. Two trans tautomers are observed, separated in energy by about 1 kcal mol-1 . Tautomerization from the higher- to the lower-energy form is detected in the lowest-excited singlet state and occurs at a rate that is about four orders of magnitude lower than that observed for porphycene. Hemiporphycene is a very good model for the investigation of inequivalent intramolecular H-bonds present in one molecule; two such bonds in HPc reveal unusual characteristics, and the bond strength results from the interplay between the N⋅⋅⋅N distance and the N-H-N angle.

Linearly dichroic plasmonic lens and hetero-chiral structures.

We present an experimental study of Hetero-Chiral (HC) plasmonic lenses, comprised of constituents with opposite chirality, demonstrating linearly dichroic focusing. The lenses focus only light with a specific linear polarization and result in a dark focal spot for the orthogonal polarization state. We introduce the design concepts and quantitatively compare several members of the HC family, deriving necessary conditions for linear dichroism and several comparative engineering parameters. The HC lenses were experimentally investigated using aperture-less near field scanning microscope collecting the amplitude of the plasmonic near-field. Our results exhibit an excellent match to the simulation predictions. The demonstrated ability for linearly dichroic functional focusing could lead to novel sensing applications.

Study of Photo-Induced Dichroism in Sudan III Doped in Poly(Methyl Methacrylate) Thin Films

Linear dichroism, dichroic ratio, contrast ratio and order parameters of Sudan III/PMMA guest host thin lms have been investigated with visible polarized laser light. Dichroism increased in an exponential fashion with increase of the pump intensity. Light-induced dichroism and polar order of the dye molecules within the polymer network were reversible. These parameters showed fast increase in their values in an exponential fashion as the pumping process takes place. Also, they decay rapidly in an exponential fashion when the pump light is cut o . Photoisomerisation and polar orientation are dependent on both the molecular structure of the dye and polymer. Two forms of Sudan III molecules (trans and cis) are responsible for the interaction with laser light and forming an anisotropic structure inside the PMMA/Sudan III lms. However, there is another set of forms of the dye (keto and enol) has to be considered, which may contribute to dichroism.