The time-resolved degenerate four-wave mixing in a nearly degenerate quasi-two-level system is treated rigorously in this paper. It is shown that quantum beat effect exists in the time-resolved degenerate four-wave mixing. The behavior of the quantum beat are analysed and its possible applications are discussed.
Based on the quasi-classical theory on the interaction of laser and matter,the characteristics of heavy and light-hole quantum beat of degenerated four-wave mixing in In_xGa_(1-x)N/GaN quantum well have been analyzed by solving the Bloch equations. The model used for describing the phenomena can be considered as a three-level system consisting of the ground state and two excited states from which the wave packet is formed and the model is a Λ-type system. It is shown that the intensity of the oscillation detected in degenerated four-wave mixing is modulated with real time and has the typical characteristics of quantum beat. The period of the beat increase with the increase of In content (x).When x=0.125,the period is 120 fs and when x=0.25,the period is 180 fs.The intensity and the amplitude of the oscillation of the sighal have great dependence on the dephasing rate of the quentum well and increase with the derease of the dephasing rate.
Time-resolved four-wave-mixing experiments are usually interpreted in terms of noninteracting two-level systems in order to obtain information on the polarization dephasing time T2. Recent experiments involving excitonic resonances in semiconductor quantum wells (including results presented in this paper) show striking qualitative deviations from this simple picture. In particular, an exponential tail is observed at low excitation for negative time delays. At high excitation, the four-wave-mixing signal is found to evolve into two distinct temporal maxima. We demonstrate that the microscopic origin of this time dependence can be understood in terms of coherent exciton-exciton interactions. We show in fact that this behavior is more general and should be seen in numerous dense media where strong nonlinear interactions of polarizations occur. In addition to presenting rigorous numerical results, we analyze two simple situations in which such interactions exist: dielectric media with local-field effects and the anharmonic oscillator. We derive analytical expressions for their time-dependent four-wave-mixing response and discuss the physical origin of these new nonlinear-optical effects.