Ring beam shaping optics fabricated with ultra-precision cutting for YAG laser processing

In this study, a method for generating ring intensity distribution at a refraction-type lens with an aspheric element was proposed, and the beam shaping optical element was finished using only ultra-precision cutting. The shape of the optical element and its irradiance pattern were determined from numerical calculation based on its geometrical and physical optics. An ultra-precision lathe was employed to fabricate beam shaping optical elements, and acrylic resin was used as the material. The transmittance of an optical element (a rotationally symmetrical body) with an aspheric surface fabricated using a single-crystal diamond tool was over 98%, and its surface roughness was 9.6 nm Ra. The method enabled the formation of a circular melting zone on a piece of stainless steel with a thickness of 300 μm through pulse YAG laser (λ 1:06 μm) processing such that the average radius was 610 μm and the width was 100–200 μm. Circular processing using a ring beam shaping optical element can be realized by single-pulse beam irradiation without beam scanning.     

Optical properties of arrays of Si nanopillars on the (1 0 0) surface of crystalline Si

We studied Si nanopillars arrays interesting for potential applications in both photonics and electronics. Two types of the Si nanopillars arrays were investigated. The first type is a regular array (square lattice with the spacing of 270 nm) made up of nanopillars with diameters of 60–70 nm (non-quantum nanopillars). Polarized reflection spectra displaying photonic band gap features and the corresponding photonic band structures were studied. The second type is a non-regular array made up of nanopillars with diameters of 10–20 nm (quantum nanopillars). Enhancement of the optical phonon Raman band, change of selection rules and a low-frequency shift of 0.5 cm⁻¹ of the band corresponding to the quantum size effect in Si cylinders with average diameter 15 nm were observed for the quantum nanopillars.     

Classification of minimal actions of a compact Kac algebra with amenable dual on injective factors of type III

We classify a certain class of minimal actions of a compact Kac algebra with amenable dual on injective factors of type III. The structural analysis of type III factors and the canonical extension of endomorphisms introduced by Izumi are our main technical tools.     

Surface plasmon resonance immunosensor for histamine based on an indirect competitive immunoreaction

The use of a surface plasmon resonance immunosensor for the analysis of histamine (β-imidazole ethylamine) is described. The method is based on an indirect competitive reaction of an anti-histamine antibody in a sample solution with histamine immobilized on a sensor chip and with histamine in the sample solution. A sensor chip immobilized with histamine was prepared using a self-assembly monolayer of 11-mercaptoundecanoic acid (11-MUA) as an anchor membrane, followed by an amino-coupling reaction with histamine after activation of the 11-MUA layer on the sensor chip by treatment with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide and N-hydroxysuccinimide. The sensor chip can be reused, after regeneration with a 10 mM HCl solution, which dissociates the anti-histamine antibody complex from histamine on the sensor chip. The affinity constants for the immunocomplex of the anti-histamine antibody with histamine in the solution and for that of the anti-histamine antibody with histamine immobilized on the sensor chip were calculated to be 1.5 × 10⁷ and 7.2 × 10⁵ M⁻¹, respectively, by assuming a Langmuir-type adsorption of the anti-histamine antibody to histamine immobilized on the sensor chip. The detection limit of the method was determined to be 3 ppb.     

A palm-sized surface plasmon resonance sensor with microchip flow cell

A small-sized surface plasmon resonance (SPR) sensor with a microchip flow cell has been developed for the purpose of enhancing the sensitivity of the SPR detector for low molecular weight compounds. This portable differential SPR detector consisted of an LED, two cylindrical lenses, a round prism, a divided mirror, a CCD, electronics, and a polydimethylsiloxane/gold microchip with two flow paths (10 mm long, 1 mm wide, 20-100 μm deep). 3-Mercaptopropyltrimethoxysilane was used for sealing the microchip. The performance of the on-site orientated SPR detector was estimated using sucrose and IgA. A drastic change in the SPR intensity appeared. The depth of the flow cell was in inverse proportion to the SPR intensity. Compared to a conventional flow cell having the size of 10 mm (L) × 1 mm (W) × 1 mm (D), its sensitivity to 10% sucrose and 0.9 nM IgA increased about 11 and 39 times, respectively. This phenomenon seemed to be due to the increase in the substance on the SPR sensor based on its size effect. These results showed that the application of the microchip sensor for SPR measurement has the possibility for improvement of the SPR intensity for low molecular substances.     

Synthesis and electrophoretic deposition of high-dielectric-constant SrTiO3 nanoparticles

We have investigated on the synthesis of SrTiO₃ nanoparticles whose bulk exhibits dielectric constant of 300, and their colloidal dispersion. As a result, we successfully synthesized SrTiO₃ nanoparticles with an average diameter of 134–485 nm measured by a scanning electron microscopic observation. The SrTiO₃ nanoparticles with a negative charge (ζ = −25 to −31 mV) can be dispersed as colloidal nanoparticles in water, and the average diameter in the dispersion were 138–356 nm measured by a dynamic light scattering technique. The colloidal dispersion of SrTiO₃ nanoparticles is promising for fabrication of low-voltage organic field-effect transistors (FETs) by a wet-processing fabrication. We have also successfully prepared SrTiO₃ films with a thickness of 1–10 μm on n-doped silicon substrates by an electrophoretic deposition technique. The SrTiO₃ films on the silicon substrates are likely used as dielectric gate insulator to low-voltage organic FETs after a sintering treatment.     

Magnetic circular dichroism near the Fermi level

We report the observation of enhanced magnetic circular dichroism (MCD) near the Fermi level using visible and ultraviolet lasers. More than 10% MCD asymmetry is achieved for a perpendicularly magnetized 12 ML (monolayer) Ni film on Cu(001). By changing the work function with the aid of cesium adsorption, the MCD asymmetry of is found to be enhanced only near the photoemission threshold and to drop down to 0.1% at the photon energy larger than the work function by 0.6 eV. A theoretical calculation also shows enhanced MCD near the photoemission threshold, qualitatively in agreement with the experimental results. Other ultrathin films of 6 ML Ni, 15 ML Co, and 3 and 15 ML Fe on Cu(001) are also investigated. It is found that the perpendicularly magnetized films show much larger MCD asymmetries than the in-plane magnetized films as in the Kerr effect.     

Conclusive evidence of an attosecond pulse train observed with the mode-resolved autocorrelation technique

We report on the direct observation of an attosecond pulse train with a mode-resolved autocorrelation technique. The chirp among the three harmonic fields is specified by analyzing two-photon above-threshold ionization spectra of electrons, resulting in a pulse duration that should be shorter than 450 as, which is, to our knowledge, the first determination of the chirp in the attosecond pulse train with an autocorrelation technique. These results will open the way to full characterization of an attosecond pulse train with its envelope.     

Focusing of light by negative refraction in a photonic crystal slab superlens on silicon-on-insulator substrate

We experimentally demonstrate the light focusing by negative refraction in a photonic crystal slab superlens at wavelengths lambda of 1.26-1.42 microm. The photonic crystal slab was fabricated on silicon-on-insulator substrate with an interface structure optimized for low reflection and diffraction losses. The light focusing in the photonic crystal slab was clearly observed through the intentional out-of-plane radiation or scattering of guided light in the slab. The minimum focused spot width was limited to 1.8 microm(1.4 lambda) owing to aberrations. The focusing characteristics were in good agreement with those obtained from photonic band and finite-difference time-domain analyses.     

Electronic transport properties of the Ising quantum Hall ferromagnet in a Si quantum well

Magnetotransport properties are investigated for a high mobility Si two-dimensional electron system in the vicinity of a Landau level crossing point. At low temperatures, the resistance peak having a strong anisotropy shows large hysteresis which is attributed to Ising quantum Hall ferromagnetism. The peak is split into two peaks in the paramagnetic regime. A mean field calculation for the peak positions indicates that electron scattering is strong when the pseudospin is partially polarized. We also study the current-voltage characteristics which exhibit a wide voltage plateau.