Interactions between coherent optical phonons and excitonic quantum beats in GaAs/AlAs multiple quantum wells: strategy for enhancement of terahertz radiation from coherent optical phonons

Abstract

AbstractWe have investigated the dynamical properties of coherent longitudinal optical (LO) phonons and excitonic quantum beats in GaAs/AlAs multiple quantum wells with various layer thicknesses, utilizing a reflection‐type pump‐probe technique and an optical gating method with a photoconductive dipole antenna. It is found that the pump‐probe signal of the coherent GaAs‐like LO phonon is markedly enhanced under the energy‐resonance condition of the LO phonon and the quantum beat due to the fundamental heavy‐hole and light‐hole excitons. This enhancement is caused by the coupling between the coherent LO phonon and excitonic quantum beat via the longitudinal polarization; namely, the quantum beat acts as a driving force for the coherent LO phonon. On the basis of this finding, we have demonstrated that the terahertz radiation from the coherent LO phonon is considerably intensified at room temperature by the longitudinal polarization coupling described above. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)