Comparison of Two Two-Photon Dressed Rules in Multi-Wave Mixing

For the first time, we report a novel two-photon dressed rule in a five-level ⁸⁵Rb atomic system. In comparison with a traditional two-photon dressed rule where the signals move with probe field frequency detuning changing, the novel one indicates that the signals do not move with coupling field frequency detuning changing. The finding is verified by the experimentally detected transmitted probe, multi-wave mixing, and fluorescence signals. We also find that the fluorescence signals show Autler-Townes splitting, which are observed experimentally and explained theoretically. By scanning one coupling field frequency detuning, variation of the dressing strength of another coupling field is revealed. Finally, we demonstrate that the alternation can be phase controlled if one of the incident beams deviates an angle (i.e., change from a normal state to an abnormal state).