THz generation from resonant excitation of semiconductor nanostructures: Investigation of second-order nonlinear optical effects

This paper reviews recent experiments on the generation of free-space terahertz (THz) radiation by all-optical excitation of semiconductor nanostructures using second-order nonlinear effects. It is focused on resonant excitation schemes only, in which so-called shift and injection currents may be generated, depending on the polarization state of the excitation pulse and on the symmetry of the semiconductor structure. In particular, the generation of such currents by interband excitation of (110)-oriented GaAs/Al0.3Ga0.7As quantum Wells with a 150-fs laser pulse is discussed and it is shown that the resonant excitation of the lowest exciton transitions in these nanostructures allows for the observation of interesting and surprising effects.