Papers by Author: Yasuhiko Benino

Abstract: We investigated the crystallization behavior of langasite-type phases in the stoichiometric corresponding glasses, i.e., Na2CaGe6O14, Na2SrGe6O14 and Pb3Ga2Ge4O14. The langasite-type phases singly were formed by heat-treatment in the glasses. Raman spectroscopy revealed the structural similarity on the scale of short-/medium-range order between the langasite-type phases and the corresponding glasses. Furthermore, we also examined the temperature dependence of second-harmonic (SH) intensity of the langasite-type phases. The SH-temperature curves exhibited an anomalous behavior, implying a structural change, e.g., isomorphous phase transition.

Abstract: Transparent nano-crystallized glass fibers with 300μm diameter were successfully fabricated in tellurite (TeO2) based glass systems. Structure of crystallized glass fibers and orientation of nano-size crystals were quantitatively investigated by microscopic Raman spectroscopy and X-ray diffraction. Second harmonic generation was measured in the nano-crystallized optical fibers.

Abstract: Homogeneous crystal lines were fabricated at the surface of 8Sm2O3.37Bi2O3.55B2O3 glass by irradiations of cw Nd: YAG laser (λ=1064 nm) with laser powers of 0.7-0.9 W and laser scanning speeds of 3-5 μm/s. It was confirmed from micro-Raman scattering spectra that the lines consist of nonlinear optical SmxBi1-xBO3 crystals showing second harmonic generations. The curved crystal lines with bending angles of 0∼90° were successfully written by just changing laser scanning directions. The light (λ=632.8 nm) transmission was confirmed for a crystal line (length: 850 μm) with two bending angles of ±30o, where significant light scattering losses were not observed at the bending points. We propose that the curved crystal lines written by YAG laser irradiations have a high potential for applications in optical waveguides.

Abstract: A high magnetic field of H = 10 T was applied to 30BaO-15TiO2-55GeO2 glass through its crystallization process. It was found that the c-axis of Ba2TiGe2O8 optical nonlinear/ferroelectric crystals oriented along the magnetic field. The second harmonic intensity of crystallized glass which the high magnetic field was applied perpendicular to the surface of glass was enhanced compared with a conventional crystallization in no magnetic field. Transparencies, photorefractive indices and thicknesses were also measured. As a result, crystal orientation of Ba2TiGe2O8 in glass matrix induced by a high magnetic field causes improvement of transparency and low value of photorefractive index.

Abstract: New crystallized glasses with nonlinear optical properties are developed by various thermal processes for glassy materials which involve the precisely controlled heat-treatment and the novel crystallization patterning using laser spot heating technique. The nonlinear optical functions and their applications are discussed based on the morphologies of the precipitated crystalline phases. The enhancement of the nonlinear optical properties can be expected by introduction of internal stress during the thermal process.

Abstract: Investigations for space-selected structure ordering from nano-particles to single-crystal patterning in glasses will be described. Transparent crystallization in glass must be the best material solution to obtain novel functional glasses with a permanent second-order optical nonlinearity. We focus on the new functions created by structure ordering in glass by means of laser micro-fabrication for space-selected crystallization. Two topics in our recent experimental results of space-selected structure ordering in glass will be presented as follows: 1) Single crystalline patterning by atom heat laser processing in Sm-doped glasses for optical waveguides with second-order optical nonlinearity, 2) structure ordering of domains in crystallized glass fibers for possible photonic fiber-type devices with active signal processing.