Time-resolved optical characterization of InAs/InGaAs quantum dots emitting at 1.3 mu m

We present the time-resolved optical characterization of InAs/InGaAs self-assembledquantum dots emitting at 1.3 μm at room temperature. The photoluminescence decay time varies from 1.2 (5 K) to 1.8 ns (293 K). Evidence of thermalization among dots is seen in both continuous-wave and time-resolved spectra around 150 K. A short rise time of 10±2 ps is measured, indicating a fast capture and relaxation of carriers inside the dots

Coherent control of polariton parametric scattering in semiconductor microcavities

In a pump-probe experiment, we have been able to control, with phase-locked probe pulses, the ultrafast nonlinear optical emission of a semiconductor microcavity, arising from polariton parametric amplification. This evidences the coherence of the polariton population near k = 0, even for delays much longer than the pulse width. The control of a large population at k = 0 is possible although the probe pulses are much weaker than the large polarization they control. With rising pump power the dynamics of the scattering get faster. Just above threshold the parametric scattering process shows unexpected long coherence times, whereas when pump power is risen the contrast decays due to a significant pump reservoir depletion. The weak pulses at normal incidence control the whole angular emission pattern of the microcavity

Comparison of radiative and structural properties of 1.3 µm InxGa(1-x)As quantum-dot laser structures grown by metalorganic chemical vapor deposition and molecular-beam epitaxy: Effect on the lasing properties

The authors have studied the radiative and structural properties of identical InxGa(1-x)As quantum dot laser structures grown by metalorg. CVD (MOCVD) and MBE. Despite the comparable emission properties found in the two devices by photoluminescence, electroluminescence, and photocurrent spectroscopy, efficient lasing from the ground state is achieved only in the MBE sample, whereas excited state lasing was obtained in the MOCVD device. Such a difference is ascribed to the existence of the internal dipole field in the MOCVD structure, induced by the strong faceting of the dots, as obsd. by high-resoln. TEM. [on SciFinder (R)

fMRI scanner noise interaction with affective neural processes

The purpose of the present study was the investigation of interaction effects between functional MRI scanner noise and affective neural processes. Stimuli comprised of psychoacoustically balanced musical pieces, expressing three different emotions (fear, neutral, joy). Participants (N=34, 19 female) were split into two groups, one subjected to continuous scanning and another subjected to sparse temporal scanning that features decreased scanner noise. Tests for interaction effects between scanning group (sparse/quieter vs continuous/noisier) and emotion (fear, neutral, joy) were performed. Results revealed interactions between the affective expression of stimuli and scanning group localized in bilateral auditory cortex, insula and visual cortex (calcarine sulcus). Post-hoc comparisons revealed that during sparse scanning, but not during continuous scanning, BOLD signals were significantly stronger for joy than for fear, as well as stronger for fear than for neutral in bilateral auditory cortex. During continuous scanning, but not during sparse scanning, BOLD signals were significantly stronger for joy than for neutral in the left auditory cortex and for joy than for fear in the calcarine sulcus. To the authors' knowledge, this is the first study to show a statistical interaction effect between scanner noise and affective processes and extends evidence suggesting scanner noise to be an important factor in functional MRI research that can affect and distort affective brain processes

Vacuum field Rabi splitting in a semiconductor microcavity

We do not intend to give here a background knowledge on vacuum field Rabi splitting. The reader should refer to J.M. Raimond, T. Norris, H. Yokoyama and D.S. Citrin lecture notes. For the sake of completeness we simply remind the reader that the cavity quantum electrodynamics (CQED) treatment of a two level atomic system resonantly coupled to a single photon mode predicts that the eigenstates of the system are no longer the photon and atomic oscillator states but two mixed symmetric and anti symmetric states. The energy separation is Δn=ℏΩ=g1‾√+n where g is a coupling factor that only depends on the dipole matrix element and the cavity volume , and n is the number of photons in the cavity1. For no incoming photons, a splitting still occurs, which can be regarded as coupling between the atomic oscillator and the vacuum field of the cavity (i.e. in the absence of a driving field). This effect was first called vacuum field Rabi splitting by J. J. Sanchez-Mondragon et al.1 as it is related to the textbook case of intense field Rabi splitting2 which, in the present case, is induced by the zero point field fluctuations in the cavity. If several atomic oscillators are present it can be shown3 that, for the n=0 states, the coupling constant increases as the square root of the number N of atoms gn = 0(N)=g(1)N‾‾√. If the system is prepared in a pure atomic oscillator or photon oscillator state, it will oscillate between these two states at the Rabi frequency Ω. In a classical description, the overall system exhibits an anti-crossing behavior when both oscillators are resonant, with the two split modes corresponding to the normal modes of the system4. In an atomic transition language, one considers the system as undergoing a coherent evolution with a photon being absorbed by an atom, which subsequently emits a photon with the same energy and wave vector k, the photon being re-absorbed, and so-on. In order to observe a similar effect in a solid we need the equivalent of both atomic and photon oscillators, both of which can be obtained in a monolithic semiconductor structure