Study Of Optical Anisotropy Research Articles

(X, T)-phase diagram of TlIn(S1–xSex)2 solid solutions (x = 0, 0.02, 0.06, 0.10, 0.15 and 0.25). Temperature dependences of thermal expansion and optical anisotropy parameters

ABSTRACT Basing on dilatometric and optical anisotropy studies, we have obtained (x, T)-phase diagram for TlIn(S1–xSex)2 solid solutions in the range 0 ≤ × ≤ 0.25 of selenium concentrations. It has been found that increasing selenium concentration leads to decrease in almost all of phase transition (PT) temperatures. At the same time, the temperature Ti of PT into incommensurate phase for the polytype c = c 0 increases at the selenium concentrations higher than 0.1, and we observe a tendency to broadening of the temperature region where the incommensurate phase exists. The incommensurate–ferroelectric PT reveals a notably diffuse character. We have also demonstrated that the TlIn(S1–xSex)2 solid solutions have a polytype structure. It manifests itself in availability of additional PT in the solid solutions with 0 ≤ × ≤ 0.05. Most probably, the latter corresponds to ferroelectric transformation in the polytype with c = 16c 0.

Optical anisotropy studies of silver nanowire/polymer composite films with Mueller matrix ellipsometry

Silver nanowire (AgNW)/photosensitive polymer composite film fabricated by roll-to-roll die coating exhibits optical and electrical anisotropy, depending on the coating conditions. To clarify the relation between the optical anisotropy, the electrical anisotropy and the orientation of AgNWs, the orthogonal optical constants of the composite films were determined by Mueller matrix spectroscopic ellipsometry. Multiple-sample analysis of reflection mode Mueller matrix and polarized transmission data was performed assuming a three-layer model consisting of substrate/polymer layer/conductive layer. The effective optical constants of the conductive layer revealed that the localized surface plasmon resonances, which arise from electric oscillation of along the short axis of AgNW, are large in the crosswise direction where the sheet resistance is large. On the other hand, the surface plasmon resonance associated with the electric oscillation along the long axis of the AgNW is large in the lengthwise direction where the sheet resistance is small. It seems the optical and electrical anisotropy reflects the morphology of the composite film, where the long axis of AgNW is preferably oriented in the direction lengthwise to the coated film.

A high-accuracy universal polarimeter study of optical anisotropy and optical activity in laminated collagen membranes.

A novel method for fabricating anisotropic collagen membranes, which regulate the preferred orientation, is developed. The high-accuracy universal polarimeter (HAUP) method is used for simultaneous and quantitative evaluations of the optical anisotropy and optical activity. The evaluation of these optical quantities, enabled by the HAUP method, is beneficial to the field of tissue engineering.

Crystallization of Poly(γ-benzyll-glutamate) in Thin Film Solutions: Structure and Pattern Formation

We have investigated the formation of poly(γ- benzyl L-glutamate) (PBLG) crystals from semidilute thin film solutions. Crystallization was initiated by adding methanol, a nonsolvent. After drying, each PBLG crystal possessed an internal domain structure exhibiting a zigzag pattern consisting of parallel stripes of alternating orientations between domains. X-ray scattering and electron diffraction revealed within these crystals a pseudohexagonal packing of the PBLG α-helices with their axis oriented parallel to the plane of the substrate. On the basis of optical anisotropy studies, it could be shown that the orientation of the helix axis was parallel to the stripes. While forming in solution, the objects are assumed to consist of a hexagonal columnar liquid crystalline phase. Upon drying, lateral packing density of the helices increased and resulted in a net dilative strain perpendicular to the columns, which is supposed to cause the formation of zigzag patterns.

Study of optical anisotropy in thin molecular layers by total internal reflection ellipsometry

Variable angle total internal reflection ellipsometry (TIRE) has been utilized to reveal anisotropy in the optical response of fragmented antibody (frag-Ab) monolayer. Optical anisotropy has been taken into account in determination of optical constants of an organic layer. The orientation of frag-Ab on the surface has been characterized by using the uniaxial model in the analysis of TIRE data. Regression results have shown that the largest dimension of frag-Ab molecule (11.5nm) is oriented parallel to the gold surface with a slight tilt (13°). Due to the tilt, the distance between the recognition sites of frag-Ab and the gold surface increases resulting in an enhanced reactivity of the molecules and better steric accessibility.

Study of optical anisotropy in nonpolar and semipolar AlGaN quantum well deep ultraviolet light emission diode

This paper analyzes the optical polarization characteristics and internal quantum efficiency (IQE) of an AlGaN based polar, nonpolar, and semipolar deep ultra-violet (UV) light emitting diode (LED). A one dimensional model is used to solve drift-diffusion, Poisson equations, and 6 × 6 k·p Schrodinger equations to investigate band structure and emission characteristics. The light emission polarization ratios of c-plane, nonpolar, and semipolar AlGaN based deep UV LEDs with different Al compositions and injection current were studied. The study shows that the optical polarization of the c-plane AlGaN based deep UV LED is dominated by the out-plane polarization as the Al composition increases. For nonpolar and semipolar structures, the light polarization direction is mainly dominated by the in-plane polarized light which is good for the surface emitting. Finally, influences of the IQE by changing the p-type activation energy, growth orientation, and nonradiatve lifetime are studied in this paper.

Reversible Optical Storage Properties of Nanostructured Epoxy-Based Thermosets Modified with Azobenzene Units

Azo-containing polymers are of particular interest in the design of materials for applications in optical recording. The aim of this contribution was the synthesis and characterization of optically active epoxy-based nanostructured thermosets obtained using epoxidized poly(styrene-b-butadiene-b-styrene) (SBS) as templating agent and modified with azobenzene groups. Morphological analysis by means of atomic force microscopy, as well as an investigation about the anisotropic optical properties of the developed materials was carried out. Different types of morphologies from micelles without long-range order to nanostructures with long-range order were achieved depending on the content of epoxidized block copolymer and azobenzene, and on the extent of epoxidation of butadiene blocks. In addition, the study of optical anisotropy showed a clear dependence of the optical storage properties upon the concentration of azo-chromophore in the samples. In particular, a thermoset containing 12.3 wt % of azo-dye and 5 phr of SBS with 46 mol % of butadiene blocks epoxidized revealed a spherical micellar morphology with maximum birefringence in the order of 1.8 × 10–2 and residual fraction of birefringence of around 0.3 after several weeks of turning off the writing beam. Besides, numerous writing-erasing cycles could also be performed without photodegradation of the materials. Furthermore, comparing parent thermosets and nanostructured systems, similar birefringence values were obtained with the advantage that the latter can also be used as templates for the development of multifunctional advanced thermosetting materials with optical properties.

Studies of optical anisotropy in opals by normal incidence ellipsometry

Anisotropy of thin opal films was studied by ellipsometric technique in a visible spectral range. At normal light incidence, the ellipsometric data were directly related to anisotropy parameters measured by polarization modulation technique. In the (111)-oriented thin films, the optical anisotropy was mainly caused by internal strain-induced birefringence with anisotropy axes oriented along [110] and [-112] directions. The deviation from 180°-symmetry, which has been observed for ellipsometric parameters in the in-plane sample rotation experiments at normal incidence, was enhanced at oblique incidence and assigned to particular properties of opal. Experimental data were discussed in the model of stacked anisotropic layers.

Study of optical anisotropies in benzocyclobutene thin films for the efficient design of optical waveguide devices

We study the in-plane/out-of-plane anisotropies in refractive indices (n) and in thermo-optic coefficients (dn/dT) of benzocyclobutene (BCB) thin film on a substrate. Both nonoxidized and oxidized films are investigated. Aside from the stress-induced effects, oxidation has significant influence on the refractive index anisotropy. The dependence of the anisotropy on each of the thermal stress and the oxidation is determined quantitatively. The anisotropies in the dn/dT values are mainly caused by the thermal stress and are independent of oxidation. However, the original (stress-free) thermo-optic coefficients are obtained as isotropic and significantly different than the measured dn/dT values. Our findings have the potential to optimize the design of polarization insensitive and/or athermal BCB optical waveguide devices.

Origins of optical anisotropy in artificial atoms

The author report on a theoretical study of optical anisotropy in quantum dots. The mechanisms how shape anisotropy and strain field lead to optical anisotropy are identified by an empirical tight-binding approach. The anisotropic structure of quantum dots is shown to impose stronger confinement for the localized p orbitals aligning along the short axis. In self-assembled quantum dots, these orbitals are also seen in a higher potential produced by the strain field. As a result, the valence-band electrons prefer to occupy the orbitals aligning along the long axis, which leads to stronger optical emission polarized along that direction.

Light figure studies of optical anisotropy induced by nanoscale spatial modulation in TlInS2

Abstract The incommensurate material, TlInS 2 , with layer structure was studied by light figure spectroscopy techniques in spectral range 400–700 nm in temperature interval 80–350 K. Evolution of light figures with temperature in phase transition region was reliably established. The optic angle of TlInS 2 was found to be sample-dependent with essentially two types of critical behavior with temperature; peak-like behavior that was ascribed to a pure incommensurate phase and peak-free behavior that was attributed to the influence of the domains or defects. In latter case the samples showed symmetry forbidden rotation of optic plane with temperature. As a whole, the obtained results allow for a conclusion that incommensurate spatial modulation with correlation length at the nanoscale was contributing to biaxial anisotropy of TlInS 2 to a level of 10 −3 versus 10 −4 for basic lattice.

Optical Anisotropy of ZnSe/BeTe Superlattices Probed by Excitonic Spectroscopy

A number of publications devoted to studies of optical anisotropy of heterostructures with no-common atom at interfaces (InAs/GaP, etc.) has been published recently [1-3]. This effect is attributed to a low local syinmetry of a single interface between two different zinc-blende type structures. In heterostructures CA/C'A' (001) with no-common cations (C ≠ C') and anions (A ≠ A'), an interface consists of the two atomic planes with A—C' or A'—C bonds. In this case there exist four different types of quantum-well structures (QWs) and superlattices (SLs). The structures with similar interfaces have the D2d point symmetry and are optically isotropic in the plane of interfaces. If the bonds at the left and right interfaces are different, an ideal structure with no-common atom is characterized by the in-plane anisotropy with the principal axes [110] and [110]. The microscopical reason for this in-plane anisotropy is a mixing of heavy hole and light hole states at the interfaces [3, 4]. In this paper we present an experimental study of the in-plane optical anisotropy in novel ZnSe/BeTe type-II quantum-well structures. Samples were grown by MBE on (100)-oriented GaAs substrates with controlling the type of interfaces. Three types of ZnSe/BeTe (100/50 Α) x 20 samples were grown: with BeSe...BeSe, ZnTe. . .ZnTe and BeSe...ZnTe interfaces. Basic optical properties of excitonic transitions in the ZnSe/BeTe quantum well structures were reported recently in Refs. [5, 6]. The observed two photoluminescence lines with energy positions at ,^s 2.8 eV and 2.0 eV were related to a

Toward Level-to-Level Energy Transfers in Photosynthesis: The Fenna−Matthews−Olson Protein

The trimeric Fenna−Matthews−Olson (FMO) protein is a bacteriochlorophyll (BChl) a antenna complex, whose X-ray structure is now known at the atomic level for two green sulfur bacterial species (Prosthecochloris aestuarii and Chlorobium tepidum). Its steady-state Qy absorption spectrum at low temperature exhibits considerable structure, with at least eight bands attributable to well-defined (groups of) BChl a exciton levels. The low-temperature absorption difference spectra of Cb. tepidum trimers excited at 789 nm are correspondingly multifeatured, and they show rich spectral evolution due to femtosecond and picosecond electronic energy transfers. Global analyses of these time-dependent ΔA spectra lead to a phenomenological scenario for cascading and branching among exciton level groups responsible for specific steady-state absorption bands. The missing link in our understanding of structure−function causality in this protein stems from a lack of an ab initio theory for the effects of known protein environments on BChl a transition energies; this problem still limits our insights into the workings of spectrally heterogeneous antennas with multiple nonequivalent pigment sites. Optical anisotropy studies strongly suggest that FMO excitations are typically localized to the 7 BChl a pigments within one protein subunit, rather than delocalized over the whole trimer. This localization occurs because the resonance couplings between BChls belonging to different subunits (<20 cm-1) are several times smaller than the diagonal energy disorder (∼70 cm-1). Strong oscillations appear in the anisotropies (∼220 fs period) for pump−probe wavelengths that simultaneously overlap both of the exciton level groups responsible for the 825 and 815 nm bands in the Qy spectrum. These are not vibational coherences, but arise from quantum beating between levels with nearly perpendicular transition moments.

Optical Anisotropy Studies of Sapphire by Raman Scattering and Spectroscopic Transmission Ellipsometry

ABSTRACTOptical anisotropy of sapphire have been studied by both polarized Raman scattering and transmission variable angle spectroscopic ellipsometry (TVASE). The polarized Raman effect was measured on both c-plane (0001) and a-plane (2110) sapphire substrates. Two TO phonons (379 and 431 cm−l) and four LO phonons (418, 450, 577, and 750 cm−1) were observed when the optical axis &lt;c&gt; is perpendicular to the polarization of the incident laser beam (for both c-plane and a-plane). While only two TO phonons (379 and 431cm−1) and two LO phonons (418 and 645 cm−1) can be seen when the optical axis is parallel to the polarization for an a-plane sapphire. The optical axis of the a-plane sapphire can then be quickly determined by either maximizing or minimizing the 645 LO peak intensity with about ±10° error. TVASE measurements were carried out in the energy range of 0.75eV to 5.8eV at room temperature. Sizable off-diagonal Jones matrix elements Apst, and Aspt can be detected even with the optical axis 1° off the X-axis. This indicates that TVASE has a high sensitivity to optical anisotropy. By minimizing these off-diagonal elements and combining the Raman analysis, the optical axis orientation of an a-plane or m-plane (0110) sapphire can therefore be fully determined with an error of less than 1°.

Dipole Moment and Optical Anisotropy Studies of Mesogenic Twin Compounds, .alpha.,.omega.-Bis[(4,4'-cyanobiphenyl)oxy]alkanes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDipole Moment and Optical Anisotropy Studies of Mesogenic Twin Compounds, .alpha.,.omega.-Bis[(4,4'-cyanobiphenyl)oxy]alkanesHidemine Furuya, Satoshi Okamoto, Akihiro Abe, George Petekidis, and George FytasCite this: J. Phys. Chem. 1995, 99, 17, 6483–6486Publication Date (Print):April 1, 1995Publication History Published online1 May 2002Published inissue 1 April 1995https://doi.org/10.1021/j100017a031RIGHTS & PERMISSIONSArticle Views75Altmetric-Citations19LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (480 KB) Get e-Alerts

Optical anisotropy and spontaneous ordering in Ga0.5In0.5P: An investigation using reflectance-difference spectroscopy.

We have applied reflectance-difference spectroscopy (RDS) to the study of optical anisotropy in spontaneously ordered Ga[sub 0.5]In[sub 0.5]P grown by metal-organic chemical-vapor deposition. The degree of order in Ga[sub 0.5]In[sub 0.5]P has been associated previously with a shift of the band-gap energy [Delta][ital E][sub 0] and a crystal-field valence-band splitting [Delta][sub [ital C]]. Theoretically, both quantities are, to first order, quadratic functions of the long-range order parameter [eta], which varies from 0 to 1 for disordered and perfectly ordered Ga[sub 0.5]In[sub 0.5]P, respectively. The main RD spectral feature in partially ordered Ga[sub 0.5]In[sub 0.5]P is a bulk-induced, asymmetric peak at [ital E][sub 0] with a long tail that extends well below [ital E][sub 0] and a sharp high-energy cutoff at [ital E][sub 0]+[Delta][sub [ital C]]. We find experimentally and theoretically that the intensity of this RD spectral feature is proportional to [radical]([Delta][ital E][sub 0]) and, therefore, is linear with the order parameter. This makes RDS particularly useful for measuring the optical anisotropy of high-band-gap Ga[sub 0.5]In[sub 0.5]P. We also compare heterostructures of GaAs and Al[sub 0.5]In[sub 0.5]P on Ga[sub 0.5]In[sub 0.5]P with uncoated Ga[sub 0.5]In[sub 0.5]P in an effort to separate bulk-, surface-, and interface-induced RD spectral features.

Investigation of spontaneous ordering in GaInP using reflectance difference spectroscopy

Reflectance difference spectroscopy (RDS) is applied to the study of optical anisotropy in spontaneously ordered GaInP grown by metalorganic chemical-vapor deposition. The degree of ordering in GaInP has been associated previously with a shift of the band-gap energy ΔE0, and a crystal-field valence-band splitting ΔC. Theoretically and experimentally, both quantities are approximately proportional to the square of the order parameter, which varies from 0 to 1 for disordered and perfectly ordered GaInP, respectively. In this study, we examined a number of GaInP layers grown under conditions that yield a wide range of band-gap energies. The main spectral feature in all samples is a bulk-related, asymmetric peak at E0 with a long tail that extends well below E0 and a sharp, high-energy cutoff at E0+ΔC. The intensity of this peak is proportional to √ΔE0 and is therefore linear with the order parameter. By annealing GaInP in PH3/H2 mixtures, we find that the RD spectral features for energies between E0+ΔC and 3 eV are mainly surface induced. Evidence for a bulk-related RDS peak at E1 is also found.

A polarimetric study of optical anisotropy in the rare-earth cuprates R2CuO4

The optical dielectric function of the ac plane of rare-earth cuprate (R2CuO4) single crystals in the energy range 1.2-2.7 eV is measured in reflection by a polarimetric method. The dispersion of optical anisotropy in insulating samples is described by two oscillators separated by 0.4 eV. Conducting samples can be identified by a Drude-like contribution. The sensitivity of the applied method allows us to test surface quality and the influence of electric transport properties on optical anisotropy.

The Chromatin Fiber: Structure and Conformational Transitions as Revealed by Optical Anisotropy Studies

Structure and conformational transitions of the chromatin fiber as revealed by optical anisotropy studies are reviewed. The data in the literature do not allow a definite interpretation; in fact some of them are contradictory. The major findings are reported here and an attempt is made to analyse them with respect to the internal dynamics and the various models suggested for the organization of the chromatin fiber.

Interferometric Studies of Optical Anisotropy and Radial Differences in Orientation in Polymer Fibers

Mathematical formulas are derived for the shape of two-beam interference fringes crossing a cylindrical multilayer fiber, as well as an equation to determine the mean refractive index at any point along the diameter of the fiber. Radial birefringence of a cylindrical fiber is also reported. The derived mathematical formulas are applied to determine the variation of the refractive indices and birefringence at any point along the diameter of two polypropylene samples with draw ratios of 4 and 5.2. Refractive index values, when light vibrates parallel and perpendicular to the fiber axis, and birefringence are larger at the edges than at the bulk of the fiber. The Lorentz-Lorenz equation is applied to calculate the polarizability of the polymer material per unit volume at different points along the diameter of the fiber. The results are illustrated by microinterferograms.