Masatoshi Nara

Numerical analysis of thermal lens effect for sensitive detection on microchips.

Thermal lens microscope (TLM) is a sensitive detection method for nonfluorescent molecules and widely applied to detection in a capillary or on a microchip. In this paper, we developed a flexible design tool for TLM systems to meet various applications utilizing a microspace. The TL effect was modeled, including signal processing, and calculated by combining fluidic dynamics and wave optics software. The coincidence of the calculations and experiments was investigated by measuring the effects of optical path length or focus positions of the excitation beams on TL signals which are quite difficult to calculate by a conventional method. Good agreement was shown and the applicability of the TLM design tool was verified.

Limits of DWDM with gratings and Fabry-Perots and alternate solutions

High resolution DWDM devices based on the principles of gratings (planar, Bragg, AWG, etc.) and Fabry-Perots (etalon, Lummer-Gehrke plate, etc.) suffer from inherent limitations due to (i) temporal pulse stretching of data, and (ii) broadening of time integrated spectral (demuxed) fringes. While the relation, dνFdt >1, can account for these limitations, our analysis imply that dnF does not represent real, physical frequencies. We explain the broader implications of this interpretation in designing DWDM devices based on gratings and Fabry-Perots and illustrate how to use prisms, photonic crystals and non-linear devices for very high data rate per channel.

Anisotropic nanometal particles on TiO2 film using sol-gel method

Recently, people have become interested in fine metal particles such as Au,Ag,Pt and Pd because of their importance in applications such as optical devices, electronic devices and heterogeneous catalysis. (1 to approximately 3) In particular, anisotropic fine metal particles have been researched as one of the key technologies to light control. We propose a new technique for preparation of anisotropic Au fine particles. SiO2 film dispersed Au fine particles was prepared by sol-gel method on TiO2 film made by sputtering. Silicon alkoxides and Au salts were used as raw materials for SiO2 film dispersed Au fine particles. The gel film was given heat- treatment at 300 degrees Celsius, and then Au salts we decomposed into Au fine particles. It was identified by TEM (transmission electron microscope) observation that anisotropic Au fine particles were trapped at the interface between SiO2 film and TiO2 film. In addition, compositional distribution in depth direction was investigated. It was confirmed by X-ray photoelectron spectroscopy that Au was distributed on the interface between TiO2 film and SiO2 film and the SiO2 film surface. Furthermore, the polarized light spectrum of Au fine particles separated out on the interface between TiO2 film and SiO2 film were measured, and as a result a polarized absorption spectrum caused by a minor axis and a major axis of Au fine particles were observed.