Champs dynamiques et thermiques dans une enceinte ventilée en régimes naturel, intermédiaire et bloqué ; cas instationnaire

On étudie expérimentalement les écoulements générés par un panache, de débit volumique constant et de température croissante au cours du temps, dans une enceinte en communication avec l'extérieur par deux ouvertures situées en partie haute et basse du compartiment. Les résultats montrent l'apparition successive de trois régimes d'écoulements selon la valeur d'un nombre de Froude densitométrique calculé à partir des caractéristiques du panache, du champ thermique et de la hauteur de l'ouverture haute

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)

Three-dimensional wavelength-scale confinement in quantum dot microcavity light-emitting diodes

The authors introduce a microcavity light-emitting diode (LED) structure that uses submicrometer oxide aperture and a quantum dot active region to achieve strong 3-dimensional confinement of both the carrier distribution and the optical field. Light-current curves show optical emission for devices >=400 nm in diam. Spectroscopy on elec. pumped LEDs, with apertures ranging from 2.5 down to 0.7 micro m, show several spectral lines corresponding to cavity modes. A strong blueshift of the resonant modes for smaller apertures demonstrates the role of the oxide aperture in confining laterally the optical wave in a vol. comparable to (l/n)3. Due to the high quality factors and low mode vols., the devices could be good candidates for the demonstration of the Purcell effect under elec. pumping. [on SciFinder (R)

Anisotropy of a thermal field at dissipative scales in the case of small-scale injection

International audienceThe anisotropy of a thermal field at the level of dissipation has been studied experimentally and by means of modeling, downstream of a heated line source placed, successively, in a turbulent boundary layer and a turbulent plane jet. This situation represents anisotropic small-scale injection of a passive scalar in a turbulent medium. All three instantaneous temperature gradients have been measured. In the central region of the thermal sheet, experimental data reveal a high degree of anisotropy of temperature dissipation near the line source and return to isotropy further downstream. Comparison of measurements with modeling allows interpreting the data and estimating the return-to-isotropy time scale

Simultaneous two-state lasing in quantum-dot lasers

The authors demonstrate simultaneous lasing at 2 well-sepd. wavelengths in self-assembled InAs quantum-dot lasers, via ground-state (GS) and excited-state (ES) transitions. This effect is reproducible and strongly depends on the cavity length. By a master-equation model, the authors attribute it to incomplete clamping of the ES population at the GS threshold. [on SciFinder (R)

Quantum dot membrane external-cavity surface-emitting laser at 1.5 μm

A membrane external-cavity surface-emitting laser (MECSEL) with an InAs/InP quantum dot (QD) based gain region is demonstrated. The pumping scheme employs a 90° off-axis parabolic mirror to focus the diode laser pump beam to a nearly circular pump spot. With this pump arrangement, the QD MECSEL with SiC heat spreaders produced 320 mW output power at room temperature with direct emission in the near-infrared at 1.5 μm. We report a record value of 86 nm for the tuning range at this wavelength region, owing to a broad QD gain bandwidth and wide tunability in MECSELs.publishedVersionPeer reviewe