J. Hamazaki

Ultrafast intersubband relaxation and nonlinear susceptibility at 1.55 μm in GaN/AlN multiple-quantum wells

Using a degenerate pump–probe technique on the Brewster configuration at room temperature, we investigate the dynamics of the intersubband transition in GaN/AlN multiple-quantum wells. The relaxation dynamics is found to consist of ultrafast (∼140 fs) and slower (∼1.3 ps) components. We estimate the third-order susceptibility for the Brewster configuration to be ∼5.5×10−18 m2/V2, which indicates that its value becomes ∼2.2×10−16 m2/V2 when a light beam is parallel to the well.

Photoluminescence from the Even-Parity State in Polythiophene Derivative

The time-resolved photoluminescence spectrum of a polythiophene derivative has been analyzed from the viewpoint of the vibronic structure and its dynamics. We found that the photoluminescence (PL) originates from two vibronic coupled states which consist of the odd-parity 1 B u component and the even-parity 2 A g component. Since the fluorescences from the two states have different time constants and different vibronic structures, the PL shows a biexponential decay and a spectral change.

Ultrafast intersubband relaxation dynamics in GaN/AlN multiple quantum wells using two-color pump-probe technique

This study investigates the detail of ultrafast intersubband relaxation dynamics in GaN/AlN quantum wells. The experiment uses a two-color pump-probe technique at room temperature. Results show the temporal traces of the change in the transmittance of the probe pulses.

Ultrafast intersubband relaxation in GaN/AlN MQWs (Invited Paper)

We have investigated the ultrafast relaxation dynamics of intersubband transition (ISBT) in GaN/AlN, using a two-color pump-probe technique, in a wide energy range around the optical communication wavelength. We suggest that the origin of the signal depends on the relation between the pump and probe pulse energies. We have observed an ultrafast induced absorption signal and a slow negative component which are due to the absorption of electrons during intra-subband scattering and a carrier cooling process with a hot-phonon effect, respectively. Moreover, we clarify the origin of the inhomogeneous broadening width of the ISBT and of the intrinsic absorption width of ISBT from the detailed analyses of the result. We have reproduced the relaxation dynamics by a numerical calculation to confirm this interpretation of ISBT relaxation dynamics.

Ultrafast intersubband relaxation in GaN/AlN multiple quantum wells

We have observed intersubband transition dynamics in GaN/AlN. The relaxation dynamics consists of ultrafast and slower components. The origin of these dynamics is discussed

Ultrafast Intersubband Relaxation and Carrier Cooling in GaN/AlN multiple quantum wells

We have investigated intersubband relaxation dynamics in GaN/AlN multiple quantum wells by the two-color pump-probe technique. We have clarified the ultrafast relaxation scenario which includes thermalization and cooling processes, and found that relaxation is influenced by a hot-phonon effect.

Ultrafast intersubband relaxation at 1.55 /spl mu/m in GaN/AlN MQWs

We have observed intersubband transition dynamics in GaN/AlN MQWs at 1.55 /spl mu/m. The relaxation dynamics consists of ultrafast component of /spl sim/170 fs and slower component of /spl sim/1.1 ps. We discussed the origin of these dynamics.

Radiative transition from even-parity state in conjugated polymer

Summary form only given. In nonfluorescent /spl pi/ conjugated polymers, e.g. polydiacetylene (PDA), the dipole forbidden 2A/sub g/ state lies below the allowed 1B/sub u/ state. On the other hand, in the fluorescent polymers such as poly-(p-phenylenvinylene) (PPV) and polythiophene (PT), the 2A/sub g/ state is considered to be above the 1B/sub u/ state. Whether the polymer shows fluorescence or not is determined by the order of the 1B/sub u/ and the 2A/sub g/ states. However, the electron-phonon coupling relaxes the selection rule. Moreover, in the case where the 1B/sub u/ and 2A/sub g/ states lie close to each other, the radiative transition from the 2A/sub g/ state can be enhanced. In the research, we confirm that photoluminescence in a PT derivative contains the contribution from the 2A/sub g/ state, and conclude that the 2A/sub g/ state lies slightly below the 1B/sub u/ state in this material.

Photoluminescence dynamics in polythiophene derivative

Summary form only given. Among many conjugated polymers, polythiophene and its derivatives are attractive material for the nonlinear optical devices because they are stable for both oxygen and moisture. However, the optical excitation dynamics in polythiophenes is not sufficiently investigated. In this study, we report time-resolved photoluminescence experiments on highly ordered and disordered films of polythiophene derivative to understand the excitation dynamics.

DISTRIBUTION OF THE EFFECTIVE CONJUGATION LENGTH OF POLYTHIOPHENE DETERMINED BY ITS ABSORPTION AND |χ(3)| SPECTRA

We measured the absorption and |χ(3)| spectra around the excitonic resonance for Langmuir–Blodgett (LB) film of polythiophene derivative, poly(3-[2-((S)-2-methylbutoxy)ethyl]thiophene) at 10 K and room temperature. We derived a theoretical distribution function for the effective conjugation length taking the molecular weight distribution into consideration, and fitted the calculated absorption and |χ(3)| spectra to the experimental ones. From the fits, we estimated the average effective conjugation length to be 21 thiophene rings at 10 K, and 15 thiophene rings at room temperature.