Multiple quantum beats embedded in coupled four-wave mixings in Rb

A theoretical model for coupled four-wave mixing (FWM) processes consisted of 5 energy levels in atoms was proposed and analyzed using perturbation theory. Experimentally, by using broadband optical pulses, a series of coupled FWM processes were produced through two-photon excitation in Rb vapor and coherent signals in the ultraviolet and visible regime were obtained. Pump-probe scheme was employed to record the time varying FWM signals at two wavelengths, respectively, and multiple quantum beats were retrieved by Fourier transform from the time varying FWM signals at two wavelengths. The results show that the multiple quantum beats retrieved from the time varying FWM signals at two wavelengths are well consistent, indicating that the coherent characteristics of atomic wave packets, which are closely related to the quantum beats, can be probed by nonlinear optical frequency mixings.