Jun Sasai

Relaxation behavior of nonlinear optical response in borate glasses containing gold nanoparticles

The relaxation time of nonlinear optical response has been obtained by femtosecond pump–probe measurements for borate glasses containing gold nanoparticles prepared by conventional melt-quenching and heat treatment techniques. Size effects of gold nanoparticles on the relaxation process were investigated. The relaxation time of a fast relaxation component increases with a decrease of the particle radius. The tail of the decay curve due to a slow relaxation component increases with an increase of the particle size. These results indicate that the particle size is an important factor for relaxation processes. In addition, the tail component is very small and is not affected by the pump intensity. This shows that the borate glass matrix has superior properties in the slow relaxation process.

Crystallization effect on non-linear optical response of silicate glass and glass-ceramics containing gold nanoparticles

Abstract Silicate glasses and glass-ceramics containing gold nanoparticles have been prepared by a conventional melt-quenching method and the subsequent two-step heat treatment processes. The relaxation time of non-linear optical response of the gold nanoparticles has been evaluated from femtosecond pump–probe measurements. The gold nanoparticles are precipitated through a heat treatment. A second heat treatment leads to the precipitation of Li 2 SiO 3 nanocrystals on the gold nanoparticles. The relaxation of non-linear optical response consists of two components; one is a fast relaxation within a few picoseconds, which originates from an electron–phonon coupling process, and the other is a slow relaxation due to a thermal diffusion of excess heat from nanoparticles to the glass matrix. Crystallization does not affect the relaxation of the fast component, while the relaxation time of the slow component decreases with an increase in the degree of crystallinity. We propose that the increased thermal conductivity in precipitated crystals, i.e., Li 2 SiO 3 nanocrystals, leads to the increase in the speed of the relaxation process which works by thermal diffusion from metal particles to the matrix.

Optical second-order nonlinearity of poled borosilicate glass containing CuCl

The effect of surface etching on second-harmonic (SH) intensity and Maker fringe pattern have been examined for poled borosilicate glasses containing CuCl. A drastic decrease in the SH intensity was observed with anode-side surface etching, while such a decrease did not appear when the cathode-side surface etching was carried out. However, after 20 μm etching of the anode-side surface, a decrease in SH intensity with the cathode-side etching was observed. For some samples, the theoretical Maker fringe pattern derived on the assumption that the SH wave is generated from a thin layer near the anode-side surface is in good agreement with the experimental one. On the other hand, other samples show oscillation in the fringe, which originates from the interference of SH waves generated from both surfaces. These results suggest that the nonlinear layer is present at both surfaces, although it is much weaker near the cathode. It is thought that the origin of the nonlinearity is attributable to migration of Cu+ an...

DC-electric-field effect on CdSe nanocrystal embedded in Indium tin oxide film and its second-order nonlinearity

Abstract The effect of DC-electric-field on crystal-growth and second-order nonlinearity of CdSe nanocrystals embedded in amorphous indium tin oxide (ITO) films prepared by r.f. sputtering has been investigated. The current-voltage curves of the as-deposited films exhibit common characteristics; with raising voltage the current increases following the Ohmic law, and shows an abrupt decrease at around 36 V/cm. When samples were electrically-treated by applying a DC electric field of 50 V/cm, CdSe nanocrystals grew with the initial orientation kept unchanged as indicated by the X-ray diffraction patterns. Considering the fact that temperature of the sample surface was raised up to 250°C during the treatment, the crystal-growth occurred as a result of an increase in temperature due to the Joule heat. On the other hand, when the as-deposited films were heat-treated without applying voltage, CdSe crystallites grew with random orientations, accompanied by crystallization of ITO matrix at 400°C. From the difference in crystallization bahavior between the electrically- and heat-treated films, we infer that the preferential crystal-growth of CdSe in the electrically-treated film can be attributed to the electric field as well as the Joule heat. The second-harmonic intensity for the electrically-treated films was enhanced by two orders of magnitude compared with the as-deposited films and was twice as large as that of the heat-treated samples.

Second-Harmonic Generation in CuCl Nanocrystal-Embedded Amorphous Indium Tin Oxide Thin Film

Second-harmonic generation has been observed in CuCl-embedded amorphous indium tin oxide thin film prepared by the sputtering method even though poling has not been carried out. The incident angle dependence and polarization dependence of the intensity of the second-harmonic wave suggest that the direction of anisotropy is predominantly perpendicular to the film surface, although the anisotropy the direction of which is parallel to the film surface is also present. The latter is ascribable to the laser-induced structural change of the film.

Structure and second-order nonlinear optical properties of CuCl nanocrystal-doped thin films prepared by rf sputtering

Second-order nonlinearity of CuCl nanocrystal-doped silica and indium tin oxide (ITO) films were examined by utilizing Maker fringe method. The films were prepared by means of the rf sputtering method with silica or ITO target on which CuCl pellets were placed. X-ray diffraction patterns of the films indicate that the mean crystallite size of CuCl nanocrystals was 20 - 30 nm based on the Sherrers equation. The films exhibit second-harmonic generation. As for the films prepared at a substrate temperature of room temperature, the dependence of second-harmonic intensity on incident angle shows that the films have an optical uniaxial anisotropy with an axis perpendicular to the film surface. An orientation of CuCl nanocrystals was confirmed by X-ray diffraction patterns, but the direction of orientation depends on the sputtering condition. In contrast, the films prepared at a substrate temperature higher than 200 degree(s)C shows different incident angle dependence of second-harmonic intensity; a maximum of second-harmonic intensity appears at the incident angle of 0 degree(s). The spacings of (111), (220), and (311) planes estimated from X-ray diffraction patterns are smaller than the values of the bulk cubic structure.