Kouhei Fukumi

Fabrication of a mid-IR wire-grid polarizer by direct imprinting on chalcogenide glass

A mid-IR wire-grid polarizer with a 500 nm pitch was fabricated on a low toxic chalcogenide glass (Sb-Ge-Sn-S system) by the thermal imprinting of periodic grating followed by the thermal evaporation of Al metal. After imprinting, deposition of Al on the grating at an oblique angle produced a wire-grid polarizer. The fabricated polarizer showed polarization with TM transmittance greater than 60% at 5-9 μm wavelengths and an extinction ratio greater than 20 dB at 3.5-11 μm wavelengths. This polarizer with a high extinction ratio can be fabricated more simply and less expensively than conventional IR polarizers.

High pressure densification of lithium silicate glasses

Abstract We have carried out neutron diffraction and Raman scattering measurements on the lithium disilicate glass densified by the application of high pressure. The density of the glass increased monotonically with applied pressures up to 6 GPa. A shift of the first sharp diffraction peak (FSDP) toward larger Q vectors was found in the total structure factor S ( Q ) of the neutron diffraction spectra. The Si–O bond length in an SiO 4 tetrahedron elongated by about 0.001 nm after densification under 6 GPa, while the nearest O–O distance did not change. However, an increase in distribution of the O–O distance was found after the densification. A low energy shift of 1080 cm −1 band, which is assigned to Si–O stretching mode, was observed in Raman scattering spectra of the densified glasses. It is consistent with the increase of Si–O bond length. We deduced from these results that the densification is caused by an increase of packing density of SiO 4 tetrahedron, which is accompanied by a distortion of the tetrahedron.

ELECTRONIC STRUCTURE OF POLYCRYSTALLINE AMOO3 (A=SR OR BA)

Two strong peaks were observed in the electron energy loss spectra of polycrystalline AMoO3 (A=Sr and Ba) perovskites with metallic conductivities. One, observed at 1.7 eV, was attributed to plasmon loss originating from conduction electrons. This explains the reddish color observed. The other, located at ∼5 eV, was attributed to the charge transfer transition from the Mo4d–O2p bonding band to an unoccupied t2g band through photoemission, ultraviolet inverse photoemission, and x-ray absorption near edge structure spectra. No intense peaks were detected in the energy region between the two absorption bands (2.5<hν<3.5 ev), indicating the possibility of application in transparent conductors for the ultraviolet region.

Relationship between refractive index and density of synthetic silica glasses

The effect of impurity and density on refractive index was studied for silica glasses synthesized with direct, sol-gel, and vapor phase axial deposition (VAD) processes. Linear relationships between the refractive index and density n=Cρ+D were found in a wide wavelength region from ultraviolet to infrared. The correlation coefficient C decreased from 0.081±0.007cm3∕g at 1.707μm to 0.061±0.008cm3∕g at 0.238μm. The relationship was different from those of the VAD or direct glasses formed by high-pressure densification, that is, the coefficient increased from 0.200±0.011cm3∕g at 1.707μm to 0.229±0.012cm3∕g at 0.238μm for VAD glass. Chlorine and hydroxyl impurities affected the refractive index; however, these impurities did not cause the linear relationship. After adjusting the index according to the chlorine related effect and the effect of the sample density, the difference between the sample’s refractive indices Δ(n2−1) showed a similar dispersion relation irrespective of the synthetic process. An analysi...

Infrared wire-grid polarizer with Y2O3 ceramic substrate.

Using two-beam interference lithography and dry etching, we fabricated a mid-IR wire-grid polarizer consisting of a 350 nm pitch WSi grating on an Y(2)O(3) ceramic substrate, which has wider transparency than sapphire. The transmittance of TM polarization was greater than 70% in the 3-7 μm wavelength range without antireflection films, and the extinction ratio was over 20 dB in the 2.5-5 μm wavelength range. The wire-grid polarizer with the Y(2)O(3) ceramic substrate provides high durability and good IR transparency.

Fabrication of Achromatic Infrared Wave Plate by Direct Imprinting Process on Chalcogenide Glass

An achromatic infrared wave plate was fabricated by forming a subwavelength grating on the chalcogenide glass using direct imprint lithography. A low toxic chalcogenide glass (Sb?Ge?Sn?S system) substrate was imprinted with a grating of 1.63-?m depth, a fill factor of 0.7, and 3-?m period using glassy carbon as a mold at 253 ?C and 3.8 MPa. Phase retardation of the element reached around 30? at 8.5?10.5 ?m wavelengths, and the transmittance exceeded that of a flat substrate over 8 ?m wavelength. Fabrication of the mid-infrared wave plate is thereby less expensive than that of conventional crystalline wave plates.

High pressure effect on optical properties of cerium ion in fluoroaluminate glass

Abstract High pressure effects on optical properties of Ce3+ doped ternary fluoroaluminate (18BaF2·37CaF2·45AlF3) glass have been investigated in terms of ligand field around cerium ion. Five bands due to the 4f–5d transitions were observed in ultraviolet absorption spectra for the glass. A photoluminescence band was observed at around 300 nm under excitation at each band. The photoluminescence band shifted toward smaller energies by densifying the glass using high pressures and temperatures. An energy shift of the band was also found in in situ photoluminescence measurement under high pressure using a sapphire anvil cell. However, the shift observed under high pressure was large compared with that of the densified glass. We deduced that the large peak shift under high pressure is mainly due to a local elastic contraction around cerium ion.

Bismuth nano-particle dispersed organic composite for optical components

Bismuth is a half metal having anisotropic susceptibility and optical constants. Therefore, the crystal axis of bismuth particle can be oriented by magnetic torque under magnetic fields. Recently, bismuth nano-particles, which have spherical, plate-like and rod-like shapes, have been prepared by some chemical methods. Orientation of bismuth nanospheres in a viscous liquid was demonstrated by using in-situ observation system of x-ray diffraction under high magnetic field in this study. The anisotropic susceptibility determined from the orientation behavior was slightly smaller than that of the bulk bismuth crystal. We have successfully introduced oriented-bismuth nano-spheres into the transparent polymethyl metacrylate under high magnetic fields up to 8 T. The composite showed a difference in transmittance depending on the direction of propagation of light being parallel or perpendicular to the applied field, indicating an anisotropic nature of optical constants of the nano-particles. Transmission spectra, which were simulated on the nano-spheres oriented composite by rigorously coupled wave analysis (RCWA), indicated that the nano-sphere has larger anisotropy in optical constants than bulk bismuth.

Design and fabrication of an achromatic infrared wave plate with Sb–Ge–Sn–S system chalcogenide glass

We designed and fabricated an achromatic infrared wave plate. To examine its phase retardation characteristics, the birefringence was calculated using the effective medium theory. A wave plate with a subwavelength grating was fabricated by direct imprint lithography on a low toxic chalcogenide glass (Sb-Ge-Sn-S system) based on calculated results. As a result of imprinting onto chalcogenide glass by a glassy carbon mold, a grating with 1.63 μm depth, a fill factor of 0.7, and a 3 μm period was obtained. The phase retardation of the elements reached around 30° in the 8.5-10.5 μm wavelength range. The fabrication of the infrared wave plate is less costly compared with conventional crystalline wave plates.

Sequential implantation of halogen and copper ions in silica glass

Abstract Halogen ions (Cl, Br and I) and copper ions have been implanted in silica glass at the same dose and at energies of the order of MeV, sequentially. The coordination structure of implanted copper atoms has been studied by X-ray absorption fine structure spectroscopy. It was found that implanted Cu atoms were coordinated with two oxygen atoms in all the as-implanted glasses. Heat treatment in air caused the formation of copper–halogen bonds without the formation of halide crystals. Further heat-treatment caused the formation of halide crystals in the glasses.