Hideyuki Inouye

Ultrafast Optical Switching in a Silver Nanoparticle System

An ultrafast response of a silver nanoparticle system, as fast as 360 fs, was observed in a femtosecond optical-Kerr-shutter experiment. The ultrafast response is attributed to a self-diffraction of a pump pulse due to transient grating. We estimated χ(3) of the silver nanoparticle system to be 1.5 × 10-7 esu in the femtosecond region.

Three-Dimensional Microscopic Crystallization in Photosensitive Glass by Femtosecond Laser Pulses at Nonresonant Wavelength

We investigated three-dimensional microscopic crystallization by irradiation of femtosecond and nanosecond laser pulses at a nonresonant wavelength of 630 nm in a photosensitive glass containing Ag+ and Ce3+. The pulse widths of the lasers were 150 fs and 3 ns, respectively. By focusing the femtosecond laser beam and following heat-treatment, spot crystallization within the glass of about 10 ?m successfully occurred without surface crystallization, while the use of the nanosecond laser beam produced no crystallization. By using the femtosecond laser, it is possible to create three-dimensional structured crystallization because of the use of transparent light and the presence of a threshold for crystallization.

Optical properties of structurally modified glasses doped with gold ions

We report on the optical properties of a structurally modified silicate glass doped with Au ions. The area in the vicinity of the focal point of an 800-nm femtosecond laser in a glass sample became gray as a result of the formation of color centers after laser irradiation and turned red because of precipitation of Au nanoparticles after further annealing at 550 degrees C for 30 min. When the glass was excited by UV light at 365 nm, yellowish-white and orange-yellow emissions were observed in the laser-irradiated and the Au-nanoparticle-precipitated area, respectively. An optical Kerr shutter experiment showed that the Au nanoparticle-precipitated glass had an ultrafast nonlinear optical response, and the third-order nonlinear susceptibility was estimated to be approximately 10(-11) esu.

Optical properties of a total-reflection-type one-dimensional photonic crystal

We produced an asymmetric Fabry-Perot microcavity using total reflection, and its optical properties were investigated. The structure is considered to be a total-reflection-type 1-D photonic crystal. An electric-field enhancement of incident light in a defect layer installed inside the photonic crystal was observed by fluorescence emission from dye molecules doped into the defect layer division. We confirmed that the incident light intensity was strengthened by about 63 times in the defect layer.

Mechanism of a Terahertz Optical Kerr Shutter with a Gold Nanoparticle System

We observed an ultrafast response as fast as 240 fs in a gold nanoparticle system, in a femtosecond optical Kerr shutter experiment. We successfully demonstrate 2.5 THz optical switching. The ultrafast response of the Kerr signal is explained by a simple model taking into account the self-diffraction of the pump pulse by the generated transient grating.

PREPARATION AND FEMTOSECOND THIRD-ORDER NONLINEAR OPTICAL PROPERTIES OF CU/SIO2 COMPOSITE THIN FILMS

A multitarget sputtering method was applied to embed Cu particles in SiO2 glass thin films (Cu/SiO2 films) with a high concentration of Cu particles (18 at.%). In the optical-absorption spectra of the as-deposited Cu/SiO2 films, the absorption peak due to the surface plasmon resonance of Cu particles was observed around 580 nm. The imaginary part of the third-order nonlinear susceptibility, | Im [χ(3)]|, exhibited a peak at the absorption peak, and the maximum value was estimated to be 1.8×10-10 esu in the femtosecond time region. The nonlinear response time derived from the recovery time of the nonlinear absorption of the film was estimated to be 1.4 ps at the absorption peak of the surface plasmon.

Diffusive torsional dynamics of malachite green molecules in solid matrices probed by fluorescence decay

The torsional dynamics of phenyl rings of malachite green molecules in the excited state is studied in polymeric and monomeric glass matrices by measuring the fluorescence decay time as a function of temperature. It is shown that the phenyl rings rotate diffusively in solid polymers (polymethyl methacrylate and polyvinyl alcohol) quite rapidly even at low temperatures. To analyze the experimental results, we used the concept of microviscosity which controls the diffusive rotational motion of phenyl rings of malachite green molecules in solid matrices. By using the reaction‐rate theory, we show that a horizontal excited‐state potential surface rather than a downhill potential surface for the rotation of phenyl rings can more reasonably explain the rotational motion in polymers. If we assume that the potential is horizontal, the temperature dependence of the microviscosity can be described by Andrade equation with a definite activation energy which is known to be valid for many liquids over a wide range of temperatures. This implies that the microscopic dynamics of small molecular rotations in a solid polymer resembles the behavior in many liquids. By monitoring the fluorescence decay of malachite green molecules doped in ethanol monomeric glass during its phase transition, we show that the effects of phase transition are well represented in the fluorescence decay time. We then propose to use malachite green molecules as sensitive optical microprobes of local dynamics in various solid matrices and their phase transitions, etc.

Wavelength dependence of photoreduction of Ag+ ions in glasses through the multiphoton process

We have investigated the wavelength dependence of the photoreduction of Ag+ ions in glass irradiated by visible femtosecond pulses. These pulses, issued at wavelengths ranging from 400 to 800 nm, were nonresonant with the glass absorption. In this article, a relationship between threshold powers, wavelengths, and linear and nonlinear refractive indices is described. The nonlinear refractive index of Ag+-doped glass was measured by an optical Kerr shutter method. The wavelength dependence of threshold powers of the photoreduction is explained by considering linear and nonlinear refractive indices. The mechanism of the photoreduction is also discussed.

Femtosecond Two-Photon Response Dynamics of Photomultiplier Tubes

An intermediate state of two-photon photoemission processes in a photomultiplier tube was found and relaxation with a time constant of 270 fs was observed by time-correlated measurements using 15 fs, 800 nm optical pulses. Optical Bloch equation analysis of the signal intensity was carried out using a perturbation method.

Femtosecond Optical Kerr Effect in the Gold Nanoparticle System

We observed an ultrashort response of the gold nanoparticle system that was as fast as 240 fs in a femtosecond optical-Kerr-shutter experiment. The ultrafast response is attributed to the self-diffraction of the pump pulse due to the transient grating. We estimated χ(3) of the gold nanoparticle system to be 2.0 ×10-8 esu in the femtosecond region.