Quasi-one-dimensional polaron gas in a GaAs quantum wire
In this work we present a study of the plasmon-longitudinal-optical (LO) phonon collective excitation as a function of the quasi-one-dimensional wave vector for several electronic densities and thickness of the wires. We observed that the intra- and intersubband excitation collective energies are very sensitive to electronic density variation. This effect is more pronounced for the lower branch of the collective excitation energy and for narrower wires. Our calculations are performed using the Singwi, Tosi, Land and Sjolander (STLS) theory, at zero temperature, assuming a three-subband model, where only the first subband is occupied by electrons.
Coupled plasmon-phonon excitations in quasi-one-dimensional quantum-well wires.
The spectrum of the coupled plasmon-phonon collective excitations of a quasi-one-dimensional quantum-well wire is analyzed. Using a three-subband model the electronic polarization function is treated in detail within the random-phase approximation. It is found that, in comparison with the quasi-two-dimensional electron gas, the excitation spectrum of the quasi-one-dimensional electron gas contains additional regions free of Landau damping. The dispersion curves of the collective excitations are calculated and presented in graphical form for three different cases of subband population. It is shown that the plasmon-phonon coupling can appreciably shift the dispersion curves. In the case that more than one subband is populated, we have found additional plasmonlike intersubband modes that exist in regions observable in far-infrared optical spectroscopy.
Generation of Nearly Diffraction-Free Beams Using a New Optical System
A new optical system which can efficiently generate the nearly diffraction-free beams is proposed and its characteristics are investigated by numerical analysis. This optical system consists of a new optical element called a DCC (double-concave-cone) lens and an objective lens with a large numerical aperture, and can generate the Bessel beam and also the Bessel-Gauss beam. The maximum propagation distance of nearly diffraction-free beams generated by the system agrees with its theoretical value for the Bessel beam.