Papers by Keyword: Optical Anisotropy

Abstract: A copolymer liquid crystal with a coumarin side group is synthesized and investigated. Under different exposure energy, the thin film of copolymer is irradiated by linearly polarized ultraviolet light (LPUV). Moreover, through changing exposure temperature and annealing temperature to investigate its photoreaction properties and reorientation performance. It is made clear that the value of optical anisotropy appears maximum with the increase of exposure energy. However, with the exposure temperature increasing, the Photo-Fries rearrangement tend to be occurred and the degree of the cyclo-addition reaction is reduced. Finally, dealing the exposed film with the liquid crystal temperature, the optical anisotropy of the film has cyclical change, but the maximum anisotropy remains nearly unchanged.

Abstract: PET/PTT bicomponent filament composed of PTT and PET arranged side-by-side often manifest high curliness after being thermally stimulated at different temperature. In this article, we report an investigation of the effect of thermal stimuli on the performances of PET/PTT bicomponent filament under various temperatures. Both the original and the thermally stimulated ones were characterized by mechanical, thermal, thermo-mechanical and optical methods. The changes of other relevant properties were also discussed.

Abstract: We present a novel numerical model that simulates the anisotropic Bragg diffraction in optically anisotropic (uniaxial) acousto-optical devices. We use a non-paraxial vectorial beam propagation method adapted to optically inhomogeneous medium and arbitrary optical field distribution. The principal idea of our solving method is that since the amplitude of the spatial variation of the refractive index caused by the acoustic wave is relatively small, we can consider it as a perturbation and iterate to the exact solution of the wave equation describing the propagation of the optical field distribution. To describe anisotropic diffraction with polarization rotation, we use a fully vectorial beam propagation method (BPM) where the accuracy depends on the relative step size. The results converge rapidly to fulfill energy conservation (up to 10–3 with less than an hour of computational time). We show that the calculated angles, the space dependent intensity and polarization variations of the diffracted beams agree accurately with those predicted by theory and experiment, under Bragg diffraction condition, in various acousto-optic configurations.

Abstract: Rheo-optical and mechanical properties of Cyclic Olefin Copolymers(COC’s) with different composition have been investigated across the glass transition temperature. Accurate measurement of stress or strain-optical coefficients and elastic modulus data across the glass transition are essential for predicting optical anisotropy in many optical products like pickup lenses and waveguides in LCD backlight unit since the material of these products have both flow and thermal history from the melt to glass. To obtain stress-optic behavior in the wide frequency region including rubbery, glassy and glass transition regime, extensional bar-type device was used. A shear-sandwich tool was used in the melt region. Master curves for modulus, stress-optical and strain-optical coefficients have been obtained in wide frequency region. The stress-optical coefficients of COC’s with mol fraction of norbornene, 60 ~ 70%, showed almost constant between -8 and -9 Br at glassy region and between +920 and +1,160 Br in the melt region. Even though the glass transition temperature showed the difference of 35
, the stress-optical coefficients of COC’s with different composition showed almost same extreme values

Abstract: The complete optical gyration tensor of monoclinic pure L-arginine phosphate monohydrate (LAP) and deuterated LAP (d-LAP) crystals has been determined. Variation of the optical activity in the presence of birefringence of d-LAP crystal with pure LAP is found from the high-accuracy universal polarimeter (HAUP) method at a wavelength of 632.8 nm. The gyration tensor components in terms of rotatory power were found to be r11 = -6.6(3) º/mm, r22 = 19(2) º/mm; r33 = 49.7(7) º/mm; and r13 = -43.7(8) º/mm for the LAP, and r11 = -1.2(1) º/mm, r22 = 5.0(4) º/mm; r33 = 41.4(3) º/mm; and r13 = -38.0(4) º/mm for d-LAP at room temperature.

Abstract: The in-plane optical anisotropy of three groups of GaAs/AlGaAs quantum well structures has been studied by reflectance-difference spectroscopy (RDS). For GaAs/Al0.36Ga0.64As single QW structures, it is found that the optical anisotropy increases quickly as the well width is decreased. For an Al0.02Ga0.98As/AlAs multiple QW with a well width of 20nm, the optical anisotropy is observed not only for the transitions between ground states but also for those between the excited states with transition index n up to 5. An increase of the anisotropy with the transition energy, or equivalently the transition index n, is clearly observed. The detailed analysis shows that the observed anisotropy arises from the interface asymmetry of QWs, which is introduced by atomic segregation or anisotropic interface roughness formed during the growth of the structures. More, when the 1 ML InAs is inserted at one interface of GaAs/AlGaAs QW, the optical anisotropy of the QW can be increased by a factor of 8 due to the enhanced asymmetry of the QW. These results demonstrate clearly that the RDS is a sensitive and powerful tool for the characterization of semiconductor interfaces.