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The effect of light beams of various structures (TEM 00 , TEM 01 , annular, vortex) on films of the photochromic azobenzene-containing polymethacrylates is studied. To analyze induced anisotropy, the methods of polarization microscopy and aberrational self-action were used. The latter is convenient non-destructive method for determining induced phase profiles and the anisotropy sign. Under the influence of the polarized light in the visible range, initially amorphous polymer samples become optically anisotropic, the induced anisotropy obeys the dose law in a wide range of light powers and illumination times. The induced anisotropy can be rewritten upon re-exposure to light or erased by heating above the transition point to the isotropic state. The direction of the induced optical axis depends on the type of light polarization. By controlling the polarization and structure of a light beam, it is possible to obtain regions with a refractive index higher or lower than the original one, as well as complex distributions, including similar to those in phase converters for vortex generation. High photosensitivity in the UV and visible ranges, local response and rewritability make these materials promising for photopatterning and light-beam diagnostics. Light beams of various types induce optical anisotropy in initially amorphous polymer layer in accordance with beam polarization structure and intensity distribution. The modified regions acts as a phase converters and are visualized with polarization optical microscopy. [Display omitted] • PMDCN shows effective and local light-rewritable relief-free light-induced anisotropy. • Aberrational self-action is a convenient way to study induced anisotropy in polymers. • Light beams of various types record spatially inhomogeneous optical-phase structures. • Vortex beam can transfer anisotropy structure from converter into polymer. [ABSTRACT FROM AUTHOR]

This article is devoted to studying the optical properties of a novel single-crystal LiTi 2 O 4 thin film. A high-quality (011)-oriented LiTi 2 O 4 single-crystal thin film was prepared on a MgAl 2 O 4 (011) substrate by pulsed laser deposition. The weak in-plane optical anisotropy is discovered by Mueller-matrix spectroscopic ellipsometry, which can be attributed to the cooperative Jahn-Teller distortion in the Ti–O octahedrons. The pseudo-dielectric functions were determined in the photon energy of 1.24–5.06 eV using the ellipsometric spectra. The optical conductivity, plasma frequency, effective mass, scattering time and other dielectric-related factors are also discussed. The critical points obtained in the pseudo-dielectric functions are originated from the charge-transfer transitions of the Ti related pairs. The results demonstrate that the enhanced effective mass is responsible for the high optical transparency of LiTi 2 O 4 rather than the large high frequency dielectric constant ε ∞. • The weak in-plane optical anisotropy was first observed by MMSE. • The optical transitions in LTO are originated from charge transfer transitions of Ti related pairs or isolated Ti ions. • The optical transparency of LTO is dominantly originated from the enhanced effective mass rather than large ε ∞ . [ABSTRACT FROM AUTHOR]

Additive manufacturing has been used to fabricate photoelastic models for several years. In the 3D-printing techniques that use photosensitive resins, models are built layer by layer, and the influence of these layers on light propagation and photoelastic fringes is still ambiguous. In this study, a plane polarization arrangement is used to examine the influence of thin layers on light propagation using three disks printed along different directions. The influence of the layers on the light intensity is negligible for the disk where the layer planes are perpendicular to the direction of light propagation. Identical light polarization is observed for the disks where the layer planes are parallel to the direction of light propagation. This is consistent with a polarizer. The evaluation of the thin layers using scanning electron microscopy indicated that the influence of the microstructures on light propagation is the potential cause of these phenomena. The influence of light polarization on photoelastic fringes was presented by comparing the fringes of different disks under circularly polarized light. The results can improve the application of the 3D-printed models in photoelasticity and the understanding of the optical anisotropy of 3D-printed polymer. • The optical anisotropy caused by thin layers in the 3D-printed material was examined. • The microstructures as the potential cause of the optical anisotropy was discussed. • The influence of the optical anisotropy on photoelastic fringes was studied. [ABSTRACT FROM AUTHOR]

Langmuir films of polystyrene-block-poly(4-vinylpyridine) (PS- b -P4VP) with an azo dye, 4-[4-(phenylazo)-1-naphthylazo]phenol (Disperse Orange 13, DO13), hydrogen-bonded to the pyridine group of P4VP blocks were investigated. The surface pressure isotherms were considerably different for the copolymer dissolved in a nonselective (chloroform) and selective (toluene) solvents. The Langmuir–Blodgett (LB) and Langmuir–Schaefer (LS) films produced with PS- b -P4VP(DO13) copolymers displayed higher optically induced birefringence than the cast films owing to their nanostructured nature. The photoinduced birefringence properties were particularly enhanced when toluene was used owing to the confinement of azo chromophores in micelles consisting of a P4VP core and a PS corona. [ABSTRACT FROM AUTHOR]

Highlights: [•] Optical and structural investigation of (Lu0.4Gd0.55Sm0.05)2SiO5 single crystal. [•] Absorption and emission spectra highly influenced by optical anisotropy of material. [•] Cross-relaxation between samarium ions. [ABSTRACT FROM AUTHOR]

Abstract: Results of comparative study of the properties and potential possibilities of three polarization sensitive media are presented. Physical mechanisms of formation of optical anisotropy in these media under influence of polarized light are described. The main emphasis is made on realization of recording of the hologram of flat wave front in these media. Experimental investigations of such recording in new polymeric composites with azobenzene polycomplexes with coordinated metallic ions are done. Presence of the metallic ions in the polymeric composite provides with additional capability for control by external electric and/or magnetic fields. Conclusion about potential applicability of this medium for polarization holography is made. [Copyright &y& Elsevier]

Abstract: A wurtzite AlN epilayer grown on (0001) sapphire substrate was characterized by variable-angle spectroscopic ellipsometry. The asymmetries of the ellipsometric spectra caused by optical anisotropy were observed below and above the Brewster angle. Tanguy’s dispersion model is employed in order to determine the extraordinary and ordinary refractive indices and extinction coefficients in the spectral range of 1.5–6.5eV. In addition, the birefringence and dichroism were derived exhibiting near the band gap a maximum and a minimum, respectively. The anisotropy is attributed to the valence band ordering at the center of the Brillouin zone, in particular to the large negative crystal-field splitting, and the corresponding optical selection rules. [Copyright &y& Elsevier]

Abstract: The synthesis and properties of poly(methylmethacrylate) films containing new azobenzene materials with potential applications in eye and sensor protection devices are reported. These films offer both improved wavelength coverage and optically-induced anisotropy compared to a commercially available azo dye, disperse red-1. Films with added diethyl phthalate plasticizer exhibit enhanced optical characteristics, as evidenced by the relatively faster response time in a pump–probe experiment. Plasticized polymer films showed good mechanical, thermal and optical stability. [Copyright &y& Elsevier]

Abstract: The light-induced orientation of azobenzene side groups of a polybutadiene based liquid crystalline polymer was studied. The polymer is based on HO-terminated telechelic polybutadiene Krasol LBH 3000 grafted with 5-(4-{[4-(octyloxy)phenyl]azo}phenoxy)pentane-1-thiol units. Linearly polarized light of wavelengths 325, 365 and 488nm influenced the photoorientation process. While irradiation with the 325 and 488nm light generated optical anisotropy, UV light of 365nm resulted in isotropic films. Pre-irradiation with the 365nm light and subsequent irradiation with 325nm led to dichroic ratio of about R D =11. Further irradiation with 365nm erased the anisotropy again. [Copyright &y& Elsevier]

Substantial in-plane optical anisotropy in Y-type Langmuir–Blodgett multilayers of a hemicyanine dye interleaved with inert material arachidic acid due to dipping-induced and “substrate”-enhanced molecular orientation was demonstrated by polarized UV-visible absorption and rotation-angle second harmonic generation techniques. We gave the first direct evidence for a super-quadratic enhancement of the second harmonic intensity with increasing film thickness due to the additional in-plane polarization. [Copyright &y& Elsevier]

There are many works and interests focused on the development of optical sensors based on porous anodic aluminum oxide membranes (AAO). Normal incidence birefringence (BR) is present in AAO when is obtained from a monocrystalline aluminum substrate but his effect has been largely ignored since it is canceled out in a poly-crystalline substrate. Nevertheless, this averaging of BR limits the optical performance of AAO membranes in optical devices. In this work, we study normal incidence BR in AAO for different crystal orientations of the aluminium substrate using a polycrystalline substrate and a simple thermo-mechanical treatment to obtain millimeter size crystalline regions. We found that normal incidence BR is minimum at [100] and [111] orientations and reaches a maximum of ∼ 1.8 ⋅ 10−3 at intermediate orientations. In this case, the BR can be associated with a slight deformation of the structure perpendicular to the direction of the pores, confirmed through scanning electron microscope images. Furthermore, we propose a simple model of elliptical section pores that quantitatively explain the origin of normal incidence BR in AAO. Considering the effect of BR , the design of sensors could be improved to obtain higher quality factors or to incorporate new optical functionalities to these already versatile membranes. • Normal incidence birefringence is present in porous anodic aluminum oxide membranes. • Pretreatment to the aluminum substrate allows characterize this optical effect. • Layers of intermediate optical thicknesses produce the highest values of birefringence. • A model based on a lateral deformation of the structure explains the origin of this effect. [ABSTRACT FROM AUTHOR]