NEGATIVE ABSORPTION COEFFICIENT OF A WEAK ELECTROMAGNETIC WAVE CAUSED BY ELECTRONS CONFINED IN RECTANGULAR QUANTUM WIRES IN THE PRESENCE OF LASER RADIATION MODULATED BY AMPLITUDE

Abstract

The analytic expressions for the absorption coefficient (ACF) of a weak electromagnetic wave (EMW) by confined electrons in rectangular quantum wires (RQWs) in the presence of laser radiation modulated by amplitude are calculated by using the quantum kinetic equation for electrons with the electron-optical phonon scattering mechanism. Then, the analytic results are numerically calculated and discussed for GaAs/GaAsAl RQWs. The numerical results show that the ACF of a weak EMW in a RQW can have negative values, which means that in the presence of laser radiation (non-modulated or modulated by amplitude), under proper conditions, the weak EMW is increased. This is different from the similar problem in bulk semiconductors and from the case of the absence of laser radiation. The results also show that in some conditions, when laser radiation is modulated by amplitude, ability to increase a weak EMW can be enhanced in comparison with the use of non- modulated laser radiation. Quantum wires are one-dimensional semiconductor structures. In quantum wires, many the physical properties of the material changes significantly from the properties of normal bulk semiconductors, including optical properties (1, 2). The linear absorption of a weak EMW and the nonlinear absorption of a strong EMW in low-dimensional systems have been studied (3-6). The influence of laser radiation on the absorption of a weak EMW in normal bulk semiconductors, quantum wells and cylindrical quantum wires have been investigated using the quantum kinetic equation method (7-10). The influence of laser radiation (non-modulated and modulated by amplitude) on the absorption of a weak EMW in component superlattices has been investigated by using the Kubo-Mori method (11). However, the influence of laser radiation modulated by amplitude on the absorption of a weak EMW in RQW are still unsolved. Therefore, in this paper, we theoretically calculate the ACF of a weak EMW caused by electrons confined in a RQW in the presence of laser radiation modulated by amplitude by using the quantum kinetic equation for electrons. The electron-optical phonon scattering mechanism is considered. The results are numerically calculated for the specific case of GaAs/GaAsAl RQW. We show that the ACF of a weak EMW in a RQW can have negative values. That means that in the presence of laser radiation (non-modulated or modulated by amplitude), under proper conditions, the weak EMW is increased; and in some conditions, when laser radiation is modulated by amplitude, ability to increase a weak EMW can be enhanced in comparison with the use of non-modulated laser radiation.