Y. Mitsumori

Manipulation of 2P excitonic wave function in ZnSe

We demonstrate that the 2P excitonic wave function in ZnSe can be manipulated coherently by a phase-locked pulse pair under two-photon excitation. The symmetry of the state is directly observed by changing the polarization of the phase-locked pulse pair.

Coherent transients involving 2P excitons in ZnSe

Using resonant SHG effect and a novel spectroscopic technique which utilizes a phase-locked laser pulse pair, we have investigated the dynamical behavior of 2P excitons. The interferogram of exciton polarization has a tail of a few picoseconds. Beating structure was observed in decaying profile. This structure can be explained by polarization interference between the heavy- and light-hole excitons split by strain.

Transient optical reflectivity in layered semiconductors

Abstract The reflection dynamics of a subpicosecond optical pulse was investigated under the Brewster angle of incidence at the exciton resonance in the layered compounds GaSe. The reflected pulse has a tail of a few picosecond which allows the decay of the resonant polarization. A time oscillatory decay of the transient reflectivity was observed. This behavior can be explained by quantum beats in the polarization decay of coherently excited singlet and triplet excitons.

Ultrafast phase distortion of the transmitted pulse in GaAs quantum wells

Abstract The phase characteristics of transmitted optical pulses were investigated in the energy- and the temporal domain using the spectrally resolved cross-correlation technique. The temporal evolution of fs pulses passing through GaAs/AlGaAs quantum wells indicates a long tail due to the coherent emission from the exciton. The phase discontinuity was observed in the time-domain data. The phase of the coherent emission signal is found to differ by 180° from that of the incident light field. Furthermore, we report the pulse propagation effect when the pre-excited coherent exciton exists in the sample. The resultant data shows that the ultrashort optical pulses are strongly affected by the phase difference between the coherent emission and the coherent exciton polarization.

Manifestation of Local Magnetic Domain Reversal by Spin-Polarized Carrier Injection in (Ga,Mn)As Thin Films

Recently, we have reported that the spin-polarized holes generated by the irradiation with circularly polarized light can change the magnetization orientation of III–V ferromagnetic semiconductor (Ga,Mn)As via p–d exchange interaction. In this paper, we report that a small portion of change does not return to the initial state after the light is turned off. This residual component, named as the memorization effect, exhibits ferromagnetic characteristics. This fact strongly suggests that small magnetic domains having the perpendicular magnetic axis are rotated by photogenerated carrier spins.

Excitonic free induction decay studied with femtosecond pulse pairs

Abstract Subpicosecond coherent emission due to excitons in GaAs/AlGaAs quantum wells has been investigated by a new spectroscopic technique utilizing a two-pulse sequence of femtosecond duration laser pulses. By measuring the two-pulse interferograms of reflected pulses at the Brewster angle of incidence and that of a resonant Rayleigh scattering sequence, the polarization decay time can be obtained.

Time-resolved three-pulse photon echoes in GaSe

Time-resolved three-pulse photon echoes of the exciton in layered semiconductor GaSe are investigated by using up-conversion technique. The time-resolved echo signal depends on the separation time between the first and second pulses. The shape of the echo signal changes as the separation time increases. The time-resolved signal also depends on the waiting time between the second and third pulses. For a short waiting time, the temporal evolution of the echo signal shows an ideal photon-echo-like (Gaussian-like) shape. On the other hand, for longer waiting times, the temporal shape of the echo signal changes dramatically and has an extra peak at the arrival time of the third pulse. This behavior can be explained by spectral diffusion in the three-pulse photon echo process.

Rotation of ferromagnetically coupled Mn spins in (Ga, Mn)As by hole spins

We present experimental data obtained from ferromagnetic p-(Ga,Mn)As layers that indicate the collective rotation of ferromagnetically coupled Mn spins by optically generated spin-polarized holes through the p–d exchange interaction. The rotation occurs reversibly between the in-plane and perpendicular directions, causing a large change in perpendicular magnetization without the application of a magnetic field. Pump-and-probe experiments suggest that the rotation of Mn spins take place in the picosecond time domain.

Polarization dependence of 3-pulse four wave mixing at the exciton resonance — Quantum beat and polarization interference

The polarization dependence of 3-pulse four wave mixing (FWM) at the exciton resonance has been studied in GaSe. A quantum beat modulation can be observed in 3-pulse FWM signals. The polarization dependence of the quantum beat has also been studied. The quantum beat and the polarization interference can be experimentally distinguished by the time-integrated 3-pulse FWM.

Transient coherent emission from anisotropic semiconductors studied with phase-locked pulse pairs

Abstract The coherent emission in the direction of the reflection has been investigated under the Brewster angle of incidence by using phase-locked pulse pairs to excite resonantly the excitons in the anisotropic crystal GaSe. The interferogram of the reflected pulse has a long tail corresponding to the free induction decay signal. We also observed the phase difference between the coherent emission from the Γ4 and Γ6 excitonic polarizations in the direction of the reflection.