Nonpolarizing guided-mode resonant grating filter for oblique incidence

A new type of guided-mode resonant grating filter is described. The filter is independent of polarization state for oblique incidence. The filter has a crossed grating structure, and the plane of incidence on the filter contains the symmetric axis of the grating structure. Theoretical considerations and numerical calculations using two-dimensional rigorous coupled-wave analysis show that a rhombic lattice structure is suitable to such filters. In this configuration an incident light wave is diffracted into the waveguide and is divided into two propagation modes whose directions are symmetric with respect to the plane of incidence. In particular, when the propagation directions of the two modes are perpendicular to each other, the fill factor of grating structure can be approximately 50%. The filter was designed for an incident angle of 45 degrees. Tolerances of setting errors and fabrication errors for this filter were estimated by numerical calculations.     

Suppression of pH effect on the electrochemical deformation in polyaniline film

pH effect on the electrochemical deformation of freestanding polyaniline (PANi) film was investigated by means of electrochemomechanical deformation (ECMD) measurement. The maximum anodic expansion was found in PANi at around pH = 1.5 in aqueous acid consisted of HCl and NaCl. The deformation vs. redox charge (D−Q) plots revealed the critical differences in the deformation characteristics below and above pH = 1.5. The similar pH dependences were also observed in other acidic media. Against these results, we investigated the surface coating effect of PANi film on deformation behaviors. It was revealed that the PPy coating on PANi film successfully reduced the pH dependence of the PANi/PPy film deformation. The results indicate that the buffer layer coated on the PANi film surface decreases the ion concentration effects on the PANi deformation. The result indicates the extensive usage of PANi actuator in wide pH aqueous media.     

Fabrication of diffractive optical elements inside polymers by femtosecond laser irradiation

Bragg-type gratings were prepared by irradiation inside a series of optical polymers with femtosecond laser pulses and the preparation conditions of the grating were examined. Repeated scanning irradiation with femtosecond laser pulses formed gratings due to refractive index changes inside polymers. Among the polymers examined in the present study, polymethylpentene (PMP) showed the highest diffraction efficiency, which was an order of magnitude higher than those of other optical polymers. The density of PMP was the lowest among the polymers evaluated in the present study, and the large volume contraction based on its low density was responsible for the larger refractive index change of PMP. Furthermore, we fabricated large-area diffractive optical elements (DOEs) in PMP measuring 15 × 25 mm² by widening the scanning area.     

Optical properties of microfabricated fully-metal-coated near-field probes in collection mode

A study of the optical properties of microfabricated, fully-metal-coated quartz probes collecting longitudinal and transverse optical fields is presented. The measurements are performed by raster scanning the focal plane of an objective, focusing azimuthally and radially polarized beams by use of two metal-coated quartz probes with different metal coatings. A quantitative estimation of the collection efficiencies and spatial resolutions in imaging both longitudinal and transverse fields is made. Longitudinally polarized fields are collected with a resolution approximately 1.5 times higher as compared with transversely polarized fields, and this behavior is almost independent of the roughness of the probe's metal coating. Moreover, the coating roughness is a critical parameter in the relative collection efficiency of the two field orientations.     

Preparation and magnetic properties of electrospun CuO/NiO bimetallic nanofibers via sol–gel electrospinning

We report the fabrication and magnetic properties of the CuO/NiO bimetallic composite nanofibers prepared by sol–gel electrospinning and followed by calcination. The added precursors (copper nitrate trihydrate (CuNT) and nickel chloride hexahydrate (NiCH)) significantly influenced the fiber formation and its morphologies during electrospinning. The magnetic properties were investigated by Vibrating Sample Magnetometer and Electron Spin Resonance (ESR) curves. After calcination for the production of the metallic nanofibers, the fiber morphologies were dramatically changed depending on the added amounts of precursors ranging from 2.5 to 7.5 wt%. From the magnetic hysteresis loop (M-H curve) and ESR analysis of the calcined electrospun CuO/NiO bimetallic nanofibers, it was found that the magnetization of the calcined electrospun CuO/NiO bimetallic nanofibers with various weight ratio of CuNT:NiCH = 9:1, 1:1, and 1:9 at an applied magnetic field of 10 kOe was 0.480, 0.402, and 0.337 emu/g, respectively, indicating that the calcined electrospun CuO/NiO bimetallic nanofibers have magnetic properties.     

Selection of eutectic systems in AI2O3–Y2O3 ceramics

There are two eutectic reactions in the Al₂0₃–rich portion of the AI₂O₃-Y₂O₃ pseudo–binary system; one is the equilibrium A1₂0₃–YAG eutectic reaction at 1826%C, and the other is the metastable A1₂0₃–YAP eutectic reaction at 1702%C. Selection of the A1₂0₃–YAG and the A1₂0₃–YAP eutectics was examined in terms of cooling rate, nucleation temperature and maximum melt temperature. When the melt was cooled from 2100%C at any cooling rate, it always nucleated below the Al₂0₃–YAP eutectic temperature, therefore the Al₂0₃–YAP eutectic was selected. The Al₂0₃–YAG eutectic was selected when the melt was cooled from 1900%C at a cooling rate of less than 1 K s^-1. The selection of the two eutectic systems was determined by the nucleation temperature, although the maximum holding temperature of the melt and the cooling rate significantly affected the nucleation temperature. The structure of the melt, such as coordination of oxygen and chemical order when being heated to 2100%C may affect the nucleation behavior.