Collective inter-subband excitations of electron gas in quantum wells in infrared absorption, Raman scattering and nonlinear optical processes

Abstract

We discuss the role of collective inter-subband excitations of electron gases confined in quantum wells in infrared absorption, resonant Raman scattering and nonlinear optical processes. First, exchange as well as direct Coulomb interaction are invoked in a theoretical model to calculate the shift of the collective inter-subband modes from the single particle excitation energy. We then formulate the coupling of the collective inter-subband charge density mode to the electromagnetic field. The coupling mechanisms via exchange and direct Coulomb scattering for resonant Raman processes are discussed. An experiment is designed that can differentiate between the two mechanisms, based on their dependence on wavefunction overlap. Finally, we discuss nonlinear optical processes involving inter-subband transitions and collective excitations.