Four-wave mixing theory for two-photon generation of excitons in cuprous oxide

The experimental situation in which excitons in Cu2O are pumped directly into a state with wave vector k→=0→ by two counter-propagating laser pulses, and subsequently probed by a third, time-delayed, pulse has been theoretically investigated. It has been shown that additional electromagnetic waves are excited in the system. A specific configuration of two pump pulses and one probe pulse has been found to generate only one additional electromagnetic wave. The dependence of the time-integrated photon number in this wave on the delay time between pump and probe pulses for some values of the detuning has been investigated.