Shinichi Watanabe

The influence of a strong atomic polarizability on photodetachment processes is isolated. In a model study of ${\mathrm{K}}^{\ensuremath{-}}$ photodetachment near the $4{p}_{\frac{1}{2}}$, $4{p}_{\frac{3}{2}}$ levels of K, the polarizability (${\ensuremath{\alpha}}_{4p}\ensuremath{\simeq}600{a}_{0}^{3}$) is shown to cause a striking energy dependence of the parameters which determine the cross section. This study extends the effective range theory of O'Malley, Spruch, and Rosenberg to a broader

The moleculelike normal modes formed by a pair of correlated electrons are examined through analysis of their wave functions in a body frame of the atom. The quantum numbers used by Lin for the classification of doubly excited states are reinterpreted from the body-frame viewpoint, and their connections with the rovibrator model of Herrick and Kellman are identified. This analysis also sheds light on the limitations of the rovibrator model of two correlated electrons. Because electrons are light

We have investigated the highly nonlinear terahertz (THz) light-matter interaction in single-walled carbon nanotubes (SWNTs). The high-peak THz electric-field (∼0.7 MV/cm) and the low effective mass of carriers result in their ponderomotive energy exceeding the bandgap energy of semiconducting SWNTs. Under such an intense THz pulse irradiation, the interband excitation that results in the generation of excitons occurs, although the THz photon energy (∼4 meV) is much smaller than the gap energy o

Threshold radiant exposures for grossly apparent immediate whitening and ultrastructural alterations of melanosomes in black guinea pig skin were determined for a series of red visible laser pulses ranging from 4 x 10(-4) to 6.5 x 10(-14) s. Threshold exposures for melanosomal injury were found to be independent of pulsewidth when the pulsewidths were below the estimated thermal relaxation time of melanosomes. Threshold radiant exposures for melanosomal injury were found to increase when the pul

We report on the growth and optical properties of homogeneous, dense arrays of site-controlled, single GaAs/AlGaAs quantum dot (QD) heterostructures with periodicities as small as 300 nm. The samples were grown by organometallic chemical vapor deposition on (111)B GaAs substrates containing dense inverted pyramid recess patterns prepared by electron beam lithography and wet chemical etching. Low-temperature microphotoluminescence spectra of the samples show distinct luminescence from the QDs wit

This review focuses on several recent research activities regarding precise and fast polarization-sensitive terahertz time-domain spectroscopy systems for imaging purposes, and explains three interesting application examples. Owing to modulation techniques that have recently been developed for the evaluation of the instantaneous terahertz electric-field (E-field) vector, fast and precise terahertz polarization imaging becomes feasible. This terahertz technology enables high-resolution surface to

Energy levels of triply excited states of an atom with all three electrons in the same shell are obtained by a model calculation. The nodal pattern of an eigenfunction at the symmetry configuration plays a crucial role in the manifestation of moleculelike modes as in the case of doubly excited states. It is shown that the correlation of the three electrons leads to normal modes isomorphic to those of a molecule with ${D}_{3h}$ symmetry. The energy levels may be thus regrouped into manifolds, eac

Wave functions of doubly excited states $^{2}S$, $^{4}P^{o}$, $^{4}P$, $^{2}P^{o}$, and $^{2}D$ of the $n=2$ shell of ${\mathrm{He}}^{\ensuremath{-}}$ are studied in hypersherical coordinates. The interaction between the outer electron pair and the ${\mathrm{He}}^{+}(1s)$ open-shell core is treated by imposing boundary conditions at the core's surface and by spin recoupling. Adiabatic potential curves and the corresponding eigenvectors are studied as functions of the hyperradius $R$. Complex eff

Stereocomplex poly(lactic acid) (sc-PLA) crystallites exhibit higher mechanical strength and thermal stability than PLA homocrystallites. In sc-PLA, a hydrogen bond that governs the physical properties is formed between two enantiomeric PLA chains during crystallization. Therefore, the investigation of this hydrogen bond is essential for a better understanding of the properties of sc-PLA. Here, we report on the terahertz spectroscopy of sc-PLA films with low crystallinities. The dielectric funct

Abundance of floor-dwelling frogs was studied in the humid subtropical lowland forest of Iriomote Island, the Ryukyu Archipelago, southern Japan. Field survey was conducted monthly for 1 y, and the seasonal pattern of abundance was examined for each species. We observed 251 frogs belonging to four species of three families in a total sampling of 600 m 2 . Of these species, Microhyla ornata (66.5% of total frogs) and Fejervarya limnocharis (30.3%) were dominant in number. Total abundance of the f

We report the observation of stimulated emission in ridge quantum wire (QWR) structures at temperatures from 4.7 to 290 K. To examine the origin of the stimulated emission, the spatially and spectrally resolved microscopic images of the emission were measured. It was most likely attributed to the optical transition between the excited states in QWRs.

The Iriomote cat Prionailurus iriomotensis occurs only on Iriomote Island in the Ryukyu Archipelago of southern Japan. The population is estimated at 100 individuals and is on the decline. We examined resource overlap for prey and habitat between this species and introduced cats Felis catus by scat census and analysis of scat contents. The distribution of scats was completely different between the two species. The distribution of scats from Iriomote cats was associated with environmental factors

We present a method of developing a high-speed terahertz time-domain polarimeter based on an electro-optic sampling setup, which consists of a rapid polarization analysis of the probe optical beam within 1 ms with an angular resolution of ∼100 mrad using an electro-optic modulator (EOM). A fast optical delay line enabled us to obtain the vector waveform of the terahertz pulse within 100 ms. The setup does not utilize a manual/mechanical rotational stage, but the use of the polarization modulatio