Nano Optical Science
Advanced Energy Conversion Division Nano Optical Science Research Section
Professor : Kazunari MATSUDA
Associate Professor : Yuhei MIYAUCHI
Assistant Professor : Keisuke SHINOKITA
Program-Specific Assistant Professor : Taishi NISHIHARA
We are studying about development of novel optical science and its application for energy based on nano-science from the viewpoint of solid state physics, material science, and device engineering.
Development of Novel Optical Science and its Application for Energy
The research objectives in our group are "development of novel optical science and its application for energy based on nano-science". We are trying to open new horizon on the energy science by introduction of nano-materials, quantum optical physics, and device application. The understanding of physics of emerging quantum optical phenomena in extreme low-dimensional materials are important issues toward next generation light energy sciences.
1) Photophysics and Applications of Nanomaterials
Our research focuses on photophysical properties and applications of nanomaterials including carbon nanotubes, graphene, and atomically thin semiconductors in which distinct quantum effects dominate their physical properties. We make use of advanced optical spectroscopic techniques to clarify the physical properties of nanomaterials for developing novel energy-efficient information processing, bioimaging, and photon energy conversion technologies.
Images of optical experiment
(a), schematic of exciton dynamics in carbon nanotube with an artificially-introduced localized state (b), up-conversion luminescence image of an ensemble carbon nanotube sample (c), wavelengths of excitation and emission (d, upper), micro-photoluminescence image of an individual carbon nanotube (d, lower), comparison of the Stokes and up-conversion luminescence spectra from an individual nanotube (e).
2) Ultrafast phenomena in atomically thin-layered materials
Atomically thin-layered material including graphene comprising from monolayer carbon atoms has attracted much interest for both fundamental research and practical application because of exotic quantum states. We have investigated two dimensional transition metal dichalcogenides (MX2; M = Mo, W, X = S, Se, Te) as the layered material with coupled spin and valley indices of charge carriers (valley-pseudospin) mainly by ultrafast spectroscopy based on femtosecond laser: Generation and relaxation dynamics of electron-hole pairs, neutral excitons and charged exciton, was revealed and control of optical properties by field effect transistor (FET) device fabrication was achieved. Now the ultrafast spectroscopic technique with device fabrication is engaged in ultrafast control of valley-pseudospin phenomena in the two dimensional transition metal dichalcogenides.
A setup of ultrafast transient reflection spectroscopy based on femtosecond laser (left) and ultrafast carrier dynamics in two-dimensional transition metal dichalcogenides (right)
The ultrafast spectroscopy system based on femtosecond laser with high-repetition rate can measure time-resolved optical properties including transient reflection with femtosecond time resolution and high signal-to-noise ratio. Right figure shows ultrafast optical response of two-dimensional transition metal dichalcogenides MoSe2 measured with the ultrafast spectroscopy system. It allows us to reveal physical mechanism underlying ultrafast dynamics including generation and relaxation process of the electron-hole pair, neutral exciton and charged exciton.