Comparison of differential gain in single quantum well and bulk double heterostructure lasers

The differential gain in single quantum well and bulk double heterostructure lasers is compared. In variance with previous predictions, no differential gain enhancement is found in single quantum well structure lasers at room temperature. Only at low temperatures do the quantum well lasers possess higher differential gain than bulk double heterostructure lasers. The results have important implications in the area of high speed phenomena for these devices

Refining MOND interpolating function and TeVeS Lagrangian

The phenomena customly called Dark Matter or Modified Newtonian Dynamics (MOND) have been argued by Bekenstein (2004) to be the consequences of a covariant scalar field, controlled by a free function (related to the MOND interpolating function) in its Lagrangian density. In the context of this relativistic MOND theory (TeVeS), we examine critically the interpolating function in the transition zone between weak and strong gravity. Bekenstein's toy model produces too gradually varying functions and fits rotation curves less well than the standard MOND interpolating function. However, the latter varies too sharply and implies an implausible external field effect (EFE). These constraints on opposite sides have not yet excluded TeVeS, but made the zone of acceptable interpolating functions narrower. An acceptable "toy" Lagrangian density function with simple analytical properties is singled out for future studies of TeVeS in galaxies. We also suggest how to extend the model to solar system dynamics and cosmology, and compare with strong lensing data (see also astro-ph/0509590).Comment: accepted for publication in ApJ Letter

A comparison of amplitude-phase coupling and linewidth enhancement in semiconductor quantum-well and bulk lasers

The amplitude-phase coupling factor α (linewidth enhancement factor) is compared for typical semiconductor quantum-well and bulk double heterostructure lasers. As a direct consequence of the reduction of the differential gain, there is no reduction of α in single-quantum-well lasers compared to bulk lasers. The number of quantum wells strongly affects the amplitude-phase coupling in quantum-well lasers. It is shown that the interband transition induced amplitude-phase coupling dominates that induced by the plasma effect of carriers in typical quantum-well lasers. By considering the spontaneous emission factor in the spectral linewidth, the authors show that there is an optimal number of quantum wells for achieving the narrowest spectral linewidth

Short-coherence length superconductivity in the Attractive Hubbard Model in three dimensions

We study the normal state and the superconducting transition in the Attractive Hubbard Model in three dimensions, using self-consistent diagrammatics. Our results for the self-consistent $T$-matrix approximation are consistent with 3D-XY power-law critical scaling and finite-size scaling. This is in contrast to the exponential 2D-XY scaling the method was able to capture in our previous 2D calculation. We find the 3D transition temperature at quarter-filling and $U=-4t$ to be $T_c=0.207t$. The 3D critical regime is much narrower than in 2D and the ratio of the mean-field transition to $T_c$ is about 5 times smaller than in 2D. We also find that, for the parameters we consider, the pseudogap regime in 3D (as in 2D) coincides with the critical scaling regime.Comment: 4 pages, 5 figure