Calculation of the Nonlinear Absorption Coefficient of a Strong Electromagnetic Wave by Confined Electrons in Doping Super- Latices

Analytic expressions for the nonlinear absorption coefficient (nonlinear absorption coefficient = NAC) of a strong electromagnetic wave (laser radiation) caused by confined electrons for the case of electron — optical phonon scattering in doping superlattices (doping superlattices = DSLs) are calculated by using the quantum kinetic equation for electrons. The problem is also considered for both the absence and the presence of an external magnetic field. The dependence of the NAC on the intensity E0 and the energy ~Ω of the external strong electromagnetic wave (electromagnetic wave = EMW), the temperature T of the system, the doping concentration nD and the cyclotron frequency ΩB for case of an external magnetic field is obtained. Two cases for the absorption: Close to the absorption threshold |k~Ω− ~ω0| ¿ ε̄ and far away from the absorption threshold |k~Ω− ~ω0| À ε̄ (k = 0, ±1, ±2 . . ., ~ω0 and ε̄ are the frequency of optical phonon and the average energy of electrons, respectively) are considered. The analytic expressions are numerically evaluated, plotted, and discussed for a specific DSLs n-GaAs/p-GaAs. The computations show that the NAC in DSLs in case presence of an external magnetic field is much more greater than to it is absence of an external magnetic field. The appearance of an external magnetic field causes surprising changes in the nonlinear absorption. All the results for the presence of an external magnetic field are compared with those for the absence of an external magnetic field to show the difference. Received 29 June 2010, Accepted 17 August 2010, Scheduled 20 August 2010 Corresponding author: D. M. Hung ([email protected]).