Quantum beats in excitons in Cu2O

A theoretical study is carried out of quantum beats (QB) in the time-dependent intensities of absorption of a test pulse and of spontaneous luminescence in a Cu2O crystal under conditions of double optical resonance. It is assumed that pumping is effected by a CO2-laser pulse which dynamically couples the exciton levels 1s(Γ5+) and 2p(Γ4−,Γ5−,Γ3−Γ2−) and splits them into two or three pairs of quasi-energy levels. The frequency of the test pulse is in resonance with the frequency Γ5+ of the exciton. The corresponding intensities for various directions of the electric vector of the pump field EL, the polarization vector ξ, and the wave vector q of the test pulse are obtained. The frequency of the quantum beats is twice the Rabi frequency, which for different values of EL, ξ and q contains different sets of matrix elements of the dipole transitions between the levels 1s(Γ5+) and 2p(Γ4−,Γ5−,Γ3−Γ2−). Thus, by measuring the period of the quantum beats it is possible to determine the unknown matrix elements of the indicated transitions.