Masaki Aihara

Non-Markovian effects in transient resonant light scattering

Abstract A non-Markovian theory of transient resonant light scattering (TRLS) by pulse excitation is presented. By the proper formula for the time-resolved spectrum of the resonantly scattered radiation, it is found that the finiteness of the reservoir correlation time plays the major role in explaining the continuous transition from the luminescence-like phenomenon in the resonant case to the scattering-like one in the off-resonant case. The transient behavior of the Raman-like and luminescence-like components is clarified in the unified manner by the non-Markovian theory. As an interesting example, a non-Markovian effect in strongly disordered systems is also investigated, and the new type of oscillatory resonant scattering is predicted.

Tunneling processes between semiconductors highly excited by coherent optical fields

Abstract We study the particle tunneling between the electron-hole systems coherently excited in semiconductors which are separated by a thin insulating layer. We derive a basic expression of the tunneling current adopting a tunneling Hamiltonian model and demonstrate how characteristic features of the high-density electron-hole system appear in the tunneling current.

Transient nonlinear optical phenomena in a disordered system

Abstract The transient optical parametric effect associated with Frenkel excitons in a disordered system is analyzed. A photon-echo like phenomenon which is caused by the spectral inhomogeneity, which reflects the exciton localization due to disorder, is found to appear in a mixed crystal. The echo profile depends on the mean excitation photon energy, which should be contrasted with the ordinary echoes in atomic or molecular systems. It is emphasized that the vertex correction plays an essential role in the nonlinear optical problem in a disordered system, and the energy correlation of excitons is directly reflected in the temporal form of signal intensity.

Pump-probe spectrum in a correlated electron-hole system

Abstract The pump-probe spectra in highly excited semiconductors are calculated to clarify the quantum fluctuation effect in a dense electron-hole system. In practical electron-hole densities, center-of-mass motion of excitons as well as state-filling effect play a significant role. The analysis is based on the BCS-like pairing theory and generalized random-phase approximation is used to take the collective excitation associated with the exciton center-of-mass motion into account. It is shown that the crossover from the electron-hole BCS state to the exciton condensed state clearly manifests itself in the pump-probe spectra.

The role of quantum fluctuations in optically excited electron-hole systems

Abstract The quantum fluctuation effect in optically excited electron-hole systems is studied. The collective modes associated with the center-of-mass motion are analyzed by the random phase approximation. The correlation energy, which is a measure of the significance of fluctuation, is also evaluated.

Optical nutation effect in electron-hole BCS states

Abstract The optical nutation effect in high-density electron-hole systems is studied. Many-body effects, such as spontaneous macroscopic coherence, band-gap renormalization, the screening effect, and density-dependent relaxation effects are included in the analysis. It is found that the rapid oscillatory nutation arises from the spontaneous macroscopic coherence.

Proximity effect of electron-hole BCS state in highly excited semiconductors

Abstract Adopting a tunneling Hamiltonian model, we study the proximity effect between the high- and low-density states of electron-hole systems which are separated by a thin insulating layer. We derive the gap equation, within second order of the tunneling effect and calculate the density of states. We also show how the proximity effect appears in the single-particle tunneling current.

Optical Josephson effect in weakly coupled semiconductors

Abstract The tunneling supercurrent of electron-hole pairs between coupled semiconductors under the coherent optical excitation is predicted to arise when the phase difference between the excitation light beams exists. This coherent many-body effect is shown to be observed as the phase dependence of the transmitted light intensity.

Hot luminescence in F center under one- and two-photon excitations

Abstract The spectra of hot luminescence from F center in KCl excited by one and two photons are theoretically investigated on the basis of a vibronic model. The depolarization spectra as well as the total emission intensity are calculated, and compared with experiments in good agreement. It is also shown that the non-Markov effect plays very important roles in the vibrational relaxation.

Transient resonant light scattering by excitons in a disordered system

Abstract I present a theoretical study of the time-resolved spectrum for resonantly scattered radiation which directly reflects the exciton relaxation in a disordered system.