Resonant Terahertz Optical Sideband Generation from Confined Magnetoexcitons

We have probed the internal structure and nonlinear response of magnetoexcitons in GaAs/AlGaAs quantum wells by resonantly driving one- and two-photon internal transitions with intense terahertz electric fields. Strong near-band-gap emission lines, or optical sidebands, appear at frequencies ${\omega }_{\mathrm{NIR}}\pm 2n{\omega }_{\mathrm{THz}}$, where ${\omega }_{\mathrm{NIR}}$ is the interband exciton-creation frequency, ${\omega }_{\mathrm{THz}}$ is the frequency of the driving field, and $n$ is an integer. The intensity of the sidebands exhibits pronounced enhancement when ${\omega }_{\mathrm{THz}}$ coincides with transitions between magnetically tuned energy levels in the excitons, providing new and accurate information on the internal dynamics of excitons.