Naoyuki Kitamura

Temperature dependence of refractive index of SiO2 glass

Abstract The refractive index of silica glass has been measured in the UV and visible regions from −165.4 to 83.3°C. The wavelength dispersion at each temperature was fitted by the three-term Sellmeier equation. Analysis of the Sellmeier equation shows that the temperature dependence of the refractive index originates from the temperature shift of the observed shift of the exciton peak at around 10.4 eV.

Intermediate range structure and low-energy dynamics of densified vitreous silica

Abstract The structure and low-energy dynamics of densified vitreous silica are studied with high accuracy by neutron scattering over a wide range of momenta and energy space. The structure factors (S(Q)) indicate that the change of the SiO4 tetrahedron (the short range order) by compaction is very small, but the intermediate range structure (IMRS) represented by the first sharp diffraction peak is strongly affected. This mainly attributed to a deformation of the sixfold ring structure. The low-energy dynamics the boson peak, BP also has a strong correlation with the change of IMRS. A reduction of the intensity of the boson peak by densification, however, cannot be explained by simple models such as phonon dumping or an eigenmode of IMRS. A shrinkage of the void space, surrounded by the sixfold ring structure, is related to the suppression of the low-energy dynamics. We consider that the origin of the boson peak can be attributed to a soft mode composed of an additional degree of freedom such as the void space.

Refractive index of densified silica glass

Abstract Silica glass with OH content around 1200 ppm was densified by hot isostatic pressing (HIP) to about 1%. The wavelength dispersion of the refractive index of the densified glass was measured in the region 0.238–1.71 μm. The wavelength dispersion is well explained by the three-term harmonic oscillator model modified by the extended point dipole theory, which has two terms with resonance wavelengths in the UV region and one term in the IR region. The model suggests that the resonance wavelengths depend on the density. In the present experiment, it is deduced that the resonance wavelengths in the UV region shift to the longer-wavelength with increasing density.

Peculiar suppression of the specific heat and boson peak intensity of densified SiO2 glass

Abstract Low-energy dynamics of normal and densified vitreous silica was investigated by neutron scattering combined with the specific heat measurements. A large evolution of the Boson peak was clarified to be a suppression of the density of states at low energy, but not a peak shift as observed by Raman scattering. These results are inconsistent with a scenario based on a phonon scattering by a local density fluctuation, but consistent with soft potential model and a recent model by Nakayama.

Formation of Au Colloid Particles in Silica Glass by Ion Implantation.

Formation of Au colloid particles and their optical property have been investigated in silica glasses implanted with Au + ions at an acceleration energy of 1.5MeV and fluence levels of 10 16 -10 17 ions/cm 2 . The Au colloid particles are formed in the as-implanted glasses. It is inferred that the average radius of Au colloid particles depends on the fluence level, although the fluence level does not affect the distribution of Au atomic concentration. The heat-treatment little affects the Au atomic distribution. The Au colloid particles grow to 4.3nm in average radius during heat treatment. It is revealed that the large nonlinear optical property of the Au + -ion-implanted silica glass is attributed to the high concentration of the Au colloid particles in the narrow region.

Formation of CuCl ultrafine particles in silica glass by ion implantation

Abstract Silica glass dispersed with CuCl ultrafine particles is prepared by the implantation of 3 MeV 6 × 10 16 Cl 2+ ions cm −2 and 3 MeV6 × 10 16 Cu 2+ ions cm −2 . It is deduced that the implanted Cu ions form mainly ultrafine Cu metallic particles in the as-implanted silica glass. The ultrafine Cu metallic particles react with Cl atoms to form CuCl ultrafine particles by heating up to 900–1000°C. The number of Cu and Cl ions forming the CuCl ultrafine particles is consistent with the fluence levels of these ions. A large number of CuCl ultrafine particles can be dispersed in silica glass.

Optical properties of fluoroaluminate glasses in the UV region

Abstract Transmittance and refractive index in the ultraviolet (UV) region have been measured for glasses in the systems MgF 2 ue5f8CaF 2 ue5f8AlF 3 and BaF 2 ue5f8CaF 2 ue5f8AlF 3 . Cutoff wavelengths of these glasses are about 160 nm. Refractive index at 248 nm is 1.43 for a 20MgF 2 ·50CaF 2 ·30AlF 3 glass and 1.45 for an 18BaF 2 ·37CaF 2 ·45AlF 3 glass. Wavelength dispersion (−d n /d λ ) of these glasses at 248 nm is 0.6 times that of a silica glass. Under irradiation by 248 nm light by a KrF excimer laser, the glasses show no decrease in transmission to an accumulated dose of 5 × 10 3 J/cm 2 . These optical properties assure that the glasses can be used as lens materials in the UV region.

Laser ablation process of quartz material using F2 laser

An investigation on the laser ablative shaping (LAS) of the quartz glass has been made experimentally. F2 laser was used as the laser light source for efficient ablation of quartz material. The output beam of F2 laser was focused on to the surface of quartz plate. The ablation rate was about 10 micron m/pulse at the irradiation fluence of 2 J/cm2. A uniform ablation of quartz plate has been demonstrated using F2 laser. The waveform of incident and transmitted laser light was measured by high speed photo-tubes to observe the time dependence of the absorption. The measured waveform indicates that the absorption was small at the leading edge of the laser pulse, and a strong absorption was induced at the end of laser pulse due to the excited state absorption. These phenomena are quite similar to both in F2 and ArF laser light. We have developed a simple model in which the instantaneous absorption is proportional to the absorbed energy prior to the moment. The calculated absorption was in good agreement with the measured wave- form. The change of transmittance in UV and VUV region was measured after the irradiation of F2 laser for samples of different concentrations of impurities.

Density and Refractive Index of Densified Silica Glass

Silica glasses with the OH content about 1200ppm and 100ppm have been densified with a HIP apparatus at temperatures of 1000-1300°C under pressures of 100-200MPa for 2 hours. The density of both glasses increases in proportion to the pressure at a fixed temperature. Under a fixed pressure, the density increases with the increase of temperature up to about 1100°C and reaches at constant values. The temperature to attain the constant density is slightly lower in the high-OH glass than in the low-OH glass, because the OH species decrease the viscosity of glass. Refractive index increases almost linearly with the increase in density with the same slope for both glasses. The relationship is explained well by the extended point dipole theory.