Nonlinear coherent spectroscopy in a degenerate two-level atomic ensemble for a transition Fg=0↔Fe=1Fg=0↔Fe=1

In this paper, nonlinear coherent spectroscopy in a degenerate two-level system for transition Fg=0↔Fe=1Fg=0↔Fe=1 is investigated. The system is pumped by a linearly polarized light of arbitrary intensity and probed by a weak light with linear polarization orthogonal to the pump light. The amplitude equations are obtained by decomposing the optical Bloch equation into its Fourier amplitude equations. The absorption and dispersion of probe beam, four-wave mixing response are calculated and discussed. It is shown that the system experience from positive to negative dispersion at zero pump–probe detuning when changing the Zeeman splitting. Four-wave mixing response can be controlled by the Rabi frequency or the Zeeman splitting. The spectra are essentially different and more complex than that of a pure two-level system.