COULOMB ENHANCEMENT OF ULTRAFAST NONLINEARITIES IN QUANTUM-WELL STRUCTURES

The Coulomb interaction among photoexcited virtual carriers or virtual excitons in two-dimensional heterostructures is theoretically considered by using bare-states and the dressed-states approaches. It is shown that, if the wave functions of the ground and the excited states are spatially separated, then the Coulomb interaction causes coherent pulsations of the transition energy. As a result, significant (an order of magnitude) enhancement of the dynamic Stark shift and of other ultrafast nonlinearities can be achieved. The enhancement of ultrafast nonlinearities is evaluated as a function of the geometry, the doping level, broadening, and other parameters. The effects of the Coulomb interaction on coherent transient phenomena is considered. The problem of practical realization of the predicted effects is addressed.