22 research outputs found
Temperature dependence of polarization relaxation in semiconductor quantum dots
The decay time of the linear polarization degree of the luminescence in
strongly confined semiconductor quantum dots with asymmetrical shape is
calculated in the frame of second-order quasielastic interaction between
quantum dot charge carriers and LO phonons. The phonon bottleneck does not
prevent significantly the relaxation processes and the calculated decay times
can be of the order of a few tens picoseconds at temperature K,
consistent with recent experiments by Paillard et al. [Phys. Rev. Lett.
{\bf86}, 1634 (2001)].Comment: 4 pages, 4 figure
Picosecond Nonlinear Relaxation of Photoinjected Carriers in a Single GaAs/AlGaAs Quantum Dot
Photoemission from a single self-organized GaAs/AlGaAs quantum dot (QD) is
temporally resolved with picosecond time resolution. The emission spectra
consisting of the multiexciton structures are observed to depend on the delay
time and the excitation intensity. Quantitative agreement is found between the
experimental data and the calculation based on a model which characterizes the
successive relaxation of multiexcitons. Through the analysis we can determine
the carrier relaxation time as a function of population of photoinjected
carriers. Enhancement of the intra-dot carrier relaxation is demonstrated to be
due to the carrier-carrier scattering inside a single QD.Comment: 4 pages, 4 figures, to be published in Phys. Rev. B, Rapid
Adiabatic steering and determination of dephasing rates in double dot qubits
We propose a scheme to prepare arbitrary superpositions of quantum states in
double quantum--dots irradiated by coherent microwave pulses. Solving the
equations of motion for the dot density matrix, we find that dephasing rates
for such superpositions can be quantitatively infered from additional electron
current pulses that appear due to a controllable breakdown of coherent
population trapping in the dots.Comment: 5 pages, 4 figures. To appear in Phys. Rev.
Infrared generation in low-dimensional semiconductor heterostructures via quantum coherence
A new scheme for infrared generation without population inversion between
subbands in quantum-well and quantum-dot lasers is presented and documented by
detailed calculations. The scheme is based on the simultaneous generation at
three frequencies: optical lasing at the two interband transitions which take
place simultaneously, in the same active region, and serve as the coherent
drive for the IR field. This mechanism for frequency down-conversion does not
rely upon any ad hoc assumptions of long-lived coherences in the semiconductor
active medium. And it should work efficiently at room temperature with
injection current pumping. For optimized waveguide and cavity parameters, the
intrinsic efficiency of the down-conversion process can reach the limiting
quantum value corresponding to one infrared photon per one optical photon. Due
to the parametric nature of IR generation, the proposed inversionless scheme is
especially promising for long-wavelength (far- infrared) operation.Comment: 4 pages, 1 Postscript figure, Revtex style. Replacement corrects a
printing error in the authors fiel
Organic compounds destruction by a relativistic eleсtron beam in waste-waters
The electron beam influence on the decomposition of organic compounds in effluents has been investigated. In
the tests, waste-water has been processed with a relativistic electron beam of the energy 3...4 MeV, formed with a
linear resonance accelerator. The model samples of the following solutions have been put on trial: nitrite-, nitrate-,
ammonium- and phosphate ions, glucose and purified kerosene. The results of the investigations have indicated that
the application of relativistic electron beams is prospective for the water purification from these organic compounds.Виконано цикл досліджень по впливу релятивістського електронного пучка на руйнування модельних
зразків розчинів нітрит-іонів, нітрат-іонів, амонійного іону, фосфат-іонів, глюкози, гасу. Показано, що
використовування релятивістських електронних пучків є перспективним для очистки стічних вод від цих
сполук.Выполнен цикл исследований по влиянию релятивистского электронного пучка на разрушение модельных образцов растворов нитрит-ионов, нитрат-ионов, амонийного иона, фосфат-ионов, глюкозы, керосина.
Показано, что использование релятивистских электронных пучков является перспективным для очистки
сточных вод от этих соединений
First tidal disruption events discovered by SRG/eROSITA: X-ray/optical properties and X-ray luminosity function at z < 0.6
High Energy Astrophysic
Unbound states in quantum heterostructures
We report in this review on the electronic continuum states of semiconductor Quantum Wells and Quantum Dots and highlight the decisive part played by the virtual bound states in the optical properties of these structures. The two particles continuum states of Quantum Dots control the decoherence of the excited electron – hole states. The part played by Auger scattering in Quantum Dots is also discussed
Nonlinear optics and saturation behavior of quantum dot samples under continuous wave driving
The nonlinear optical response of self-assembled quantum dots is relevant to the application of quantum dot based devices in nonlinear optics, all-optical switching, slow light and self-organization. Theoretical investigations are based on numerical simulations of a spatially and spectrally resolved rate equation model, which takes into account the strong coupling of the quantum dots to the carrier reservoir created by the wetting layer states. The complex dielectric susceptibility of the ground state is obtained. The saturation is shown to follow a behavior in between the one for a dominantly homogeneously and inhomogeneously broadened medium. Approaches to extract the nonlinear refractive index change by fringe shifts in a cavity or self-lensing are discussed. Experimental work on saturation characteristic of InGa/GaAs quantum dots close to the telecommunication O-band (1.24-1.28 mm) and of InAlAs/GaAlAs quantum dots at 780 nm is described and the first demonstration of the cw saturation of absorption in room temperature quantum dot samples is discussed in detail