Quantum beats of excitons in Cu2O at double optical resonance

The quantum beats (QB) in the tim-dependent absorption intensity of the probe pulse and the spontaneous luminescence one in Cu2O crystal at the condition of double optical resonance are studied theoretically. It is assumed that the pump is performed by the CO2 laser pulse, which couples dynamically the 1s (Gamma(5)(+)) and 2p(Gamma(4)(+), Gamma(5)(-), Gamma(3)(-), Gamma(2)(-)) excitonic states and leads to their splitting into two or three quasienergy levels. The frequency of the probe pulse is in the region of the Gamma(5)(+) exciton resonance. The respective intensities for different directions of the electric field E(L) of the pump, the polarization xi of the probe pulse, and the observation q are obtained. The QB take place with the doubled Raby frequency, which at different E(L), xi, and q includes different sets of matrix elements of dipole transitions between 1s(Gamma(5)(+)) and 2p (Gamma(4)(-), Gamma(5)(-), Gamma(3)(-), Gamma(2)(-)) levels. These unknown matrix elements can be obtained, measuring the period of the QB.