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Summary form only given. We present femtosecond time-resolved investigations of non-equilibrium coherent 1.0 phonon dynamics in CdS/sub 0.7/Se/sub 0.3/ quantum dots embedded in a glass matrix. The three-dimensional quantum confinement of the LO phonons has been demonstrated by means of linear Raman spectroscopy. For the electron and hole states the size of the microcrystallites is in the regime of...
Summary form only given. Reversible phase change materials such as compounds of the pseudo-binary GeTe-Sb/sub 2/Te/sub 3/ system are applicable as high-density optical data storage media based on the relatively high difference in the reflection coefficients of the amorphous and the crystalline states. Although this principle is already employed in commercial DVD disks, the physics of the phase transitions...
Summary form only given. In recent years, nanoparticles of metals, such as gold, silver, and copper, have attracted much attention because they have electrical and optical properties that are different from those of bulk metals. Electron dynamics and optical nonlinear response of metallic nanoparticles have been studied extensively and suggested that metallic nanoparticles are promising candidates...
Summary form only given. The physical nature of photoluminescence (PL) from semiconductor nanocrystals has been a subject of considerable debate. Earlier studies using organically-capped nanocrystals have shown that the PL arises primarily from dark excitonic states with a radiative lifetime of order microseconds. Recent advances in developing inorganically-capped nanocrystals have led to much improved...
Summary form only given. Incoherent emission (fluorescence and Raman scattering) of an ensemble of randomly oriented molecules is isotropic. However, when these molecules are homogeneously embedded in a sample shape (such as spheres, spheroids, cylinders, ...) which concentrates the internal intensity distribution, the resulting fluorescence emission can become anisotropic. Based on reciprocity principle,...
Summary form only given. Due to the discrete structure of energy levels and an enhanced surface-to-volume ratio, energy relaxation and recombination dynamics in colloidal quantum dots (QDs) are significantly different from those in bulk materials. Energy relaxation leads to a fast establishment of quasi-equilibrium populations of electron and hole quantized states (sub-ps time scale). Depopulation...
Summary form only given. We report on recent time-resolved photoluminescence (PL) measurements of CdSe-ZnSe self-assembled quantum dots. In order to visualize single dots, we take time-resolved spectra through 200-nm apertures defined through a metal film on the surface of the sample.
Summary form only given. Recently, various spectral interferometries have been developed to measure separately ultrafast phase and transmission change induced by short pulses. Our group developed a femtosecond Sagnac interferometer in order to obtain time-resolved difference phase and transmission spectra, which are hereafter abbreviated to TRDPS and TRDTS, respectively. In the present study, we obtained...
Summary form only given. Recently, we have shown how time-resolved nonlinear optical spectroscopy can be utilized to study the spin wave dynamics in strongly correlated systems. Here, we demonstrate how the same techniques can reveal physical properties of higher-energy features, such as the charge transfer (CT) gap. We have performed both linear and nonlinear, time-resolved optical spectroscopy of...
Summary form only given. Since the discovery of high transition temperature superconductivity more than decade ago a controversial debate still exists on the underlying pairing mechanism not yet resolved. A key parameter is the carrier concentration in the conducting copper-oxide planes, which, in the case of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO), is varied by altering the oxygen content...
Summary form only given. Recent experiments have revealed ultrafast optically-induced dynamics in the time-resolved magneto-optical (MO) signals obtained in metallic ferromagnetic samples. The very short time scales that have been reported seem to exclude the role of spin-lattice interactions in the dynamics and open several fundamental questions about the physical mechanism responsible for fast demagnetization...
Summary form only given. Reduction of the size of a material to a nanometric scale leads to drastic modifications of its properties. In metallic systems, they are largely conditioned by the alteration of the conduction electron scattering processes whose study is thus of both technological and fundamental interests. Time-resolved femtosecond techniques have been shown to be powerful tools for their...
Summary form only given. The emergent properties of many materials derive from strong electron correlations augmented or mediated under realistic conditions by electron-phonon interactions. An important class of materials whose electronic and transport properties are primarily determined by such many-body effects are mixed-valence manganite perovskites R/sub 1-x/D/sub x/MnO/sub 3/ where R is a trivalent...
Summary form only given. It is usually assumed that first-order interband transitions in crystalline solids occur almost vertically in the band structure since the photon momentum is negligible compared to the reciprocal lattice vector. Especially, optical excitation and probing of free excitons in direct semiconductors is considered possible only in the center of the Brillouin zone and with photon...
Summary form only given. Extensive recent studies have provided valuable understanding on the role of correlations between excitons in optical interactions in semiconductors. Few experimental and theoretical studies, however, have addressed the effects of correlations when a semiconductor is excited above the band gap. In this paper, we report studies of 4-particle correlations by using differential...
Summary form only given. Molecular J-aggregates have attracted much attention because of the ultrafast and large optical nonlinearity caused by the excitonic resonance.
Summary form only given. Recently we have introduced a new method named (TD) CARS for the preparation and monitoring of arbitrarily high vibrational wavepackets in the ground state. We use two independent time delays between the three laser fields of the CARS process. Starting from the equilibrium ground state of a molecule we excite the molecule with a short-laser pulse to a higher electronic state...
Summary form only given. The recent observation of an "atomic-like" AC Stark splitting in a semiconductor microcavity in which the Fabry-Perot mode is resonant with the fundamental quantum-well excitonic transition has opened the following question: is it possible to observe an AC Stark splitting when exciting in the exciton continuum? To answer this question we have studied the AC Stark...
Summary form only given. We exploit a high-quality semiconductor microcavity for the creation of an exciton gas near the optical saturation density. The sample is excited by short laser pulses that are resonant with both the cavity mode and the exciton transition. The microcavity provides a narrow spectral filter that strongly inhibits the photoexcitation of dissociated electron-hole pairs. On the...
Summary form only given. When a quantum-well exciton transition is resonant with a single mode of a high-Q microcavity, the normal modes ("cavity polaritons") of the coupled system are equal admixtures of the exciton and cavity. We have previously shown that, if the lower normal mode is excited by a phase-locked pair of optical pulses, the nonlinear response of a probe pulse tuned to the...
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