Moriaki Wakaki

Microlenses and microlens arrays formed on a glass plate by use of a CO 2 laser

Microlenses and microlens arrays were formed directly on a surface of a glass plate by use of a CO(2) laser. When the surface of a glass plate is heated locally to a working point of the glass material by use of a focused CO(2) laser beam, it tends to become a hyperboloid owing to surface tension, which results in a microlens. A profile of the microlens was measured with an ultrahigh accurate three-dimensional profilometer (Model UA3P, Matsusita Electric Industrial Company Ltd.) that utilizes a specially designed atomic force microscope. An intensity profile and a spot diameter at the focus of the microlens were measured with a microscope and a CCD system utilizing a He-Ne laser as a light source. The focused spot FWHM diameter of 1.35 mum was obtained, and the modulation transfer function was derived from the spot profile. Microlens arrays were also fabricated and characterized.

Magnetoabsorption in Single-Crystal HgCr2Se4

The optical absorption spectra of HgCr 2 Se 4 single crystals in the intrinsic transition region were measured as a function of magnetic field at a number of fixed temperatures. The absorption edge, 0.80 eV, at room temperature shifted to 0.27 eV at liquid helium temperature. The temperature dependence of the absorption edge was nonlinear and remarkable around the Curie temperature. The absorption edge also shifts to the lower energy side with the increasing magnetic field. The field dependence of the edge shift in weaker magnetic field was larger at the Curie temperature than it in the higher temperature region. The temperature and magnetic field dependence of the absorption edge was compared to a calculated spin correlation function in spinels with the nearest neighbour exchange interaction between localized Cr +3 ions. Other kind of exchange interaction would be required to explain the temperature dependence of the absorption edge.

Fiber-optic polarizer using birefringent crystal as a cladding

A new type of fiber-optic polarizer has been developed in which the birefringent material is formed around the core fiber as a cladding. A NaNO(3) single crystal is used as the birefringent material. The extinction ratios for the polarized light are measured for fibers with cores of various radii and claddings of various lengths. The extinction ratios obtained are typically 31.2 dB for a core diameter of 6 µm and a cladding length of 6 mm.

Development of high-dispersion grisms and immersion gratings for spectrographs of the Subaru Telescope

We show that a crystalline lithium niobate (LiNbO3 : LN) grism and a hybrid grism made of a LN transmission grating and a zinc sulfide (ZnS) prism, in spite of their birefringent properties, can be used as new and powerful dispersing elements with high refractive indices to realize high spectral resolution for optical to near infrared astronomical spectrograph with transmission optics. We also show new fabricating methods for grisms and immersion gratings with high index material and deep grooves.

Laser-induced forward transfer of TiO2–Au nanocomposite films for maskless patterning

Laser-induced forward transfer is investigated for maskless pattering of thin films. A 89TiO2–11Au (mol %) nanocomposite polycrystalline (100 nm thick) film fabricated by a sol-gel method shows a surface plasmon absorption produced by Au nanoclusters formed in the film. A second-harmonic generation sheet beam of a Q-switched Nd:YAG laser was irradiated on the film in air in contact with another glass substrate or with a 0.14 mm air gap. Regular stripe patterns of laser-induced transferred films were obtained. Transmittance spectra of laser-induced transferred films showed shifts of the surface plasmon absorption peak. Analysis of the spectra using the Mie scattering model revealed the porous character of transferred films.

Infrared Reflectivity Spectrum and Lattice Vibration of Spinel-Type Compound HgIn2S4

Indium thiospinel compound with normal spinel structure HgIn2S4 single crystal was synthesized by the Bridgman method, and far-infrared reflection and transmission spectra were measured in the wavelength region from 20 to 1000 cm-1. The dispersion parameters are calculated by dispersion analysis using classical oscillators. The strength of the four kinds of short-range force constant is calculated using the dynamical matrices proposed by Bruesch et al., and the effective charges for each ion are obtained under several assumptions.

Development of immersion grating for mid-infrared high dispersion spectrograph for the 8.2m Subaru Telescope

The mid-infrared high dispersion spectrograph (IRHS; tentative name) with a resolving power of 200,000 at 10 μm is a candidate of the second-generation instrument for the 8.2m Subaru Telescope. A germanium immersion grating will be employed as a dispersing element for this instrument. Germanium immersion gratings for the prototype IRHS were successfully fabricated by using a nano precision 3D profile grinding/turning machine and ELID grinding method on diamond machining. As a result, the fabricated gratings observed to have grooves with ideal saw-tooth shape, smooth surface and acceptable wave front error of a diffraction beam at 10μm. In the present paper, we characterized the performance of the developed immersion gratings.

DEVELOPMENT OF A MULTICHANNEL FOURIER TRANSFORM SPECTROMETER

We devised a novel type of multichannel Fourier transform spectrometer (MCFTS) that incorporates a Wollaston prism, polarizing interferometer combined with two Savart plates and a phase-retarding plate. This original MCFTS produces a number of lines of folded interferograms recorded with a two-dimensional imaging detector such as a CCD detector. In the present type of MCFTS, the total incident light is available except for a small amount of reflection loss. It is possible to enhance the signal-to-noise ratio. The enhancement of the resolving power is also expected by the connection of the interferograms with a newly developed method.

Optical and Electrical Properties of Inverse Spinel Compound MgIn2S4

A single crystal of MgIn2S4 was grown by Bridgman method. The crystal structure of the crystal was measured by powdered X-ray diffractometer. By comparison of integrated diffraction intensity between experimental and calculated, the partially inverse structure was best fit to the experimental. The fundamental absorption edge is positioned at 2.14 eV. By using interference fringes of thin sample and prism method, accurate dispersion curve was obtained over the wavelength range 2.5–16µ. Five vibrational modes were observed in the lattice vibration spectrum. High electrical resistivity and n type conduction was obtained at room temperature.

Optical Characteristics of Al2O3 Ceramics Doped with Cr at High Concentrations Prepared by Extrusion Molding Process

Polycrystalline Al2O3 ceramics doped with Cr (sintered ruby) up to high concentrations (0.66, 0.76 and 0.97 wt%) were fabricated with an extrusion molding process using Al2O3 and Cr2O3 powders. It was found from absorption spectra that a high concentration of Cr ions was optically activated. The fluorescence spectrum of Cr ions in the sintered ruby corresponded to that of a single crystal.