Generation of tunable hypersonic phonons from two-dimensional electron gases under free-electron laser radiations

A theoretical study of generation of high-frequency acoustic-phonon emission by electrons in GaAs-based two-dimensional electron gases (2DEGs), subject to terahertz (THz) free-electron laser radiations, is presented. We have studied the frequency and angular distribution of the phonon emission generated optically via deformation potential coupling. The distinctive nature for electron-photon-phonon interactions in a 2DEG results in a strong dependence of the acoustic-phonon emission on strength E0 and frequency ω of the THz laser field. Consequently, the frequency and the angle for hypersonic phonon emission can be tuned by varying E0 and/or ω.