Hideaki Kano

Formation of GaAs ridge quantum wire structures by molecular beam epitaxy on patterned substrates

A ridge quantum wire structure has been successfully fabricated on a patterned (001) GaAs substrate by first growing a (111)B facet structure with a very sharp ridge and then depositing a thin GaAs quantum well on its top. Electron microscope study has shown that a GaAs wire with the effective lateral width of 17–18 nm is formed at the ridge top. Photoluminescence and cathodoluminescence measurements indicate that one of the luminescence lines comes from the wire region at the ridge and its blue shift (∼60 meV) agrees with the quantum confined energy calculated for the observed wire structure.

Vibrationally resonant imaging of a single living cell by supercontinuum-based multiplex coherent anti-Stokes Raman scattering microspectroscopy

Supercontinuum-based multiplex coherent anti-Stokes Raman scattering (CARS) microspectroscopy has been applied to vibrational imaging of a living fission yeast cell. We have successfully extracted only a vibrationally resonant CARS image from a characteristic spectral profile in the C-H stretching vibrational region. Using our simple but sensitive analysis, the vibrational contrast is significantly improved in comparison with a CARS imaging at a fixed Raman shift. The CARS image of a living yeast cell indicates several areas at which the signal is remarkably strong. They are considered to arise from mitochondria.

Ultrabroadband (>2500cm−1) multiplex coherent anti-Stokes Raman scattering microspectroscopy using a supercontinuum generated from a photonic crystal fiber

We have developed ultrabroadband multiplex coherent anti-Stokes Raman scattering (CARS) microspectroscopy using a coherent supercontinuum in the near-infrared region generated from a photonic crystal fiber. Owing to the ultrabroadband Stokes radiation obtained from the supercontinuum, multiple vibrational modes can be excited simultaneously in the wave-number range of more than 2500cm−1. A CARS imaging of a lipid vesicle is demonstrated with a high vibrational contrast.

Quantitative coherent anti-Stokes Raman scattering (CARS) microscopy.

The ability to observe samples qualitatively at the microscopic scale has greatly enhanced our understanding of the physical and biological world throughout the 400 year history of microscopic imaging, but there are relatively few techniques that can truly claim the ability to quantify the local concentration and composition of a sample. We review coherent anti-Stokes Raman scattering (CARS) as a quantitative, chemically specific, and label-free microscopy. We discuss the complicating influence of the nonresonant response on the CARS signal and the various experimental and mathematical approaches that can be adopted to extract quantitative information from CARS. We also review the uses to which CARS has been employed as a quantitative microscopy to solve challenges in material and biological science.

Time-resolved fluorescence and absorption spectroscopies of porphyrin J-aggregates

Dynamics of excited states in porphyrin J-aggregates has been investigated using femtosecond time-resolved fluorescence and absorption spectroscopies. An ultrafast relaxation process due to internal conversion (IC) from the S2-exciton state to the S1-exciton state is observed as an S2-fluorescence and a recovery from a bleaching of the S2-exciton state. The S2-fluorescence shows a sharp spectrum with almost no Stokes shift with a decay-time constant of 360±70 fs. In the transient absorption spectrum, the bleaching of the S2-exciton state disappears with a time constant of about 300 fs, which is in agreement with the result of the time-resolved fluorescence data. Relaxation dynamics of the S1-exciton following S2→S1IC is also studied and several relaxation processes such as an intra-aggregate vibrational energy redistribution, vibrational and phase-space coolings are investigated.

Quantitative CARS Molecular Fingerprinting of Single Living Cells with the Use of the Maximum Entropy Method

This work was supported by the SENTAN project (Program-S) of the Japan Science and Technology Agency (JST). H. Kano gratefully acknowledges financial support from the Precursory Research for Embryonic Science and Technology (PRESTO) program of JST. The authors thank C. Onogi for providing the spontaneous Raman spectrum of yeast mitochondria, Leukos and Horus Laser companies for technical support, and Dr. F. Omura and H. Yomo (Suntory Co., Ltd.) for providing us with the yeast sample. We gratefully acknowledge J. Ukon (HORIBA, Ltd.) for assisting in the collaboration between the Japanese and French groups.

Femtosecond coherent anti-Stokes Raman scattering spectroscopy using supercontinuum generated from a photonic crystal fiber

Femtosecond time-resolved coherent anti-Stokes Raman scattering (CARS) spectroscopy is demonstrated using a Ti:Sapphire oscillator and a photonic crystal fiber. A spectrally dispersed CARS signal of cyclohexane exhibits well-defined beats with a period of 430fs, which agrees well with a frequency difference between the symmetric and antisymmetric CH2-stretching vibrational modes.

Surface diffusion processes in molecular beam epitaxial growth of GaAs and AlAs as studied on GaAs (001)‐(111)B facet structures

Mechanisms of molecular beam epitaxy have been investigated for GaAs and AlAs by growing and analyzing the shapes of facet structures consisting of an (001) top surface and two (111)B side surfaces. It is found that all of the Ga flux on the three facet planes is incorporated into the film, but the growth rates on (111)B and (001) depend strongly on the As flux and are mainly determined by the diffusion of Ga ad‐atoms between the two planes. In contrast, the diffusion of Al is found to be almost negligible, irrespective of the As flux. By analyzing the shape of the facet, the diffusion length, λ, of Ga on a (001) surface is estimated to be about 1 μm at 580 °C, while that of Al is about 0.02 μm. On (111)B, λ of Ga is found to be several μms. The reflectivity of diffusing Ga atoms is found to be far less than 1 for the (001)‐(111)B boundary, and almost unity at facet boundaries where the (111)B side surfaces are bound by the (110) side walls.

Enhanced crystallographic selectivity in molecular beam epitaxial growth of GaAs on mesas and formation of (001)‐(111)B facet structures for edge quantum wires

The crystallographic selectivity of molecular beam epitaxial growth of GaAs on mesas consisting of a (001) surface and (111)B facets is studied systematically. It was found that the growth rate on (111)B facets can be drastically reduced to ∼1/30 of the growth rate on (001) surface by the reduction of As flux on the (111)B facets. This enhanced selectivity results from the enhanced intersurface migration, and strongly indicates a feasibility of forming microheterostructures needed for the fabrication of edge quantum wires on (001)‐(111)B mesas.

In-vivo multi-nonlinear optical imaging of a living cell using a supercontinuum light source generated from a photonic crystal fiber

A supercontinuum light source generated with a femtosecond Ti:Sapphire oscillator has been used to obtain both vibrational and two-photon excitation fluorescence (TPEF) images of a living cell simultaneously at different wavelengths. Owing to an ultrabroadband spectral profile of the supercontinuum, multiple vibrational resonances have been detected through coherent anti-Stokes Raman scattering (CARS) process. In addition to the multiplex CARS process, multiple electronic states can be excited due to the broadband electronic two-photon excitation using the supercontinuum, giving rise to a two-photon excitation fluorescence (TPEF) signal. Using a living yeast cell whose nucleus is labeled by green fluorescent protein (GFP), we have succeeded in visualizing organelles such as mitochondria, septum, and nucleus through the CARS and the TPEF processes. The supercontinuum enables us to perform unique multi-nonlinear optical imaging through two different nonlinear optical processes.