Narrow Results

Recent progress and state of GaSb based type-I lasers emitting in spectral range from 2 to 3.5 μm is reviewed. For lasers emitting near 2 μm an optimization of waveguide core width and asymmetry allowed reduction of far field divergence angle down to 40-50 degrees which is important for improving coupling efficiency to optical fiber. As emission wavelength increases laser characteristics degrade due to insufficient hole confinement, increased Auger recombination and deteriorated transport through the waveguide layer. While Auger recombination is thought to be an ultimate limiting factor to the performance of these narrow bandgap interband lasers we demonstrate that continuous improvements in laser characteristics are still possible by increasing hole confinement and optimizing transport properties of the waveguide layer. We achieved 190, 170 and 50 mW of maximum CW power at 3.1, 3.2 and 3.32 μm wavelengths respectively. These are the highest CW powers reported to date in this spectral range and constitute 2.5-fold improvement compared to previously reported devices.

In this paper, long wavelength superluminal and subluminal properties of pulse propagation in a defect slab medium doped with four-level GaAs/AlGaAs multiple quantum wells (MQWs) with 15 periods of 17.5 nm GaAs wells and 15 nm ${\mathrm{\text{Al}}}_{0.3}{\mathrm{\text{Ga}}}_{0.7}\mathrm{\text{As}}$ barriers is theoretically discussed. It is shown that exciton spin relaxation (ESR) between excitonic states in MQWs can be used for controlling the superluminal and subluminal light transmissions and reflections at different wavelengths. We also show that reflection and transmission coefficients depend on the thickness of the slab for the resonance and nonresonance conditions. Moreover, we found that the ESR for nonresonance condition lead to superluminal light transmission and subluminal light reflection.

Rotation and magnetic field have a stabilizing effect on the Bénard problem if they act separately. However, as is shown in the classical works of Chandrasekhar,² when they are both present, these stabilizing effects are often conflictual. Instead, other stabilizing effects, such as rotation and concentration field, are cumulative.⁸ The previous results were obtained for stress-free boundary conditions, and fixed boundary temperatures and concentrations. In this work, we investigate, analytically and numerically,^3,13 how different boundary conditions on the temperature, such as the Robin and Neumann b.c. used in,⁴ influence the competition and cooperation of the aforesaid stabilizing effects. The appearance of long-wavelength perturbations for low thermal conductivity of the boundaries is also investigated. The present work concerns a linear stability analysis of the problem and it is part of a larger project including a nonlinear analysis.^6,13

It is known that a fluid layer heated from below,³ when the boundaries are poorly conducting, gives rise to long-wavelength instabilities (see e.g. Refs. 5,7). The same effect appears⁸ also in the case of convection in a porous medium.¹⁹ In this work we investigate, analytically and numerically,^6,18 how this effect is influenced by a stabilizing solutal field, both in the case of a fluid layer and in porous media. The solutal field is assigned through fixed concentrations at the boundaries, or more general Robin boundary conditions. The present work concerns a linear stability analysis of the problem and it is part of a larger project including a nonlinear analysis.^9,12,18

Recent progress and state of GaSb based type-I lasers emitting in spectral range from 2 to 3.5 μm is reviewed. For lasers emitting near 2 μm an optimization of waveguide core width and asymmetry allowed reduction of far field divergence angle down to 40-50 degrees which is important for improving coupling efficiency to optical fiber. As emission wavelength increases laser characteristics degrade due to insufficient hole confinement, increased Auger recombination and deteriorated transport through the waveguide layer. While Auger recombination is thought to be an ultimate limiting factor to the performance of these narrow bandgap interband lasers we demonstrate that continuous improvements in laser characteristics are still possible by increasing hole confinement and optimizing transport properties of the waveguide layer. We achieved 190, 170 and 50 mW of maximum CW power at 3.1, 3.2 and 3.32 μm wavelengths respectively. These are the highest CW powers reported to date in this spectral range and constitute 2.5-fold improvement compared to previously reported devices.