The influences of confined phonons on the nonlinear absorption coefficient (NAC) by a strong electromagnetic wave for the case of electron-optical phonon scattering in doped superlattices (DSLs) are theoretically studied by using the quantum transport equation for electrons. The dependence of NAC on the energy (Ω), the amplitude E 0 of external strong electromagnetic wave, the temperature (T) of the system, is obtained. Two cases for the absorption: Close to the absorption threshold |k Ω − ω 0 | ε and far away from the absorption threshold |k Ω − ω 0 | ε (k = 0, ±1, ±2,. .. , ω 0 andε are the frequency of optical phonon and the average energy of electrons, respectively) are considered. The formula of the NAC contains a quantum number m characterizing confined phonons. The analytic expressions are numerically evaluated, plotted and discussed for a specific of the n-GaAs/p-GaAs DSLs. The computations show that the spectrums of the NAC in case of confined phonon are much different from they are in case of unconfined phonon and strongly depend on a quantum number m characterizing confinement phonon.
Abstract-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 E 0 and the energy Ω of the external strong electromagnetic wave (electromagnetic wave = EMW), the temperature T of the system, the doping concentration n D and the cyclotron frequency Ω B for case of an external magnetic field is obtained. Two cases for the absorption: Close to the absorption threshold |k Ω − ω 0 | ε and far away from the absorption threshold |k Ω − ω 0 | ε (k = 0, ±1, ±2 . . ., ω 0 andε 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.
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