Doppler-free three-photon coherence in Doppler-broadened diamond-type atomic system.

We investigated the relationship between three-photon electromagnetically induced absorption (TPEIA) and four-wave mixing (FWM) in the 5S-5P-5D transition of Rb atoms. When the driving field was additionally coupled to the ground and intermediate states of a lower V-type configuration in a typical ladder-type electromagnetically induced transparency (EIT) system, Doppler-free TPEIA and FWM spectra were simultaneously observed and then analyzed from the perspective of multi-photon atomic coherence. Comparing the TPEIA and FWM spectra according to the laser frequency detuning and laser intensity, we found that the enhanced TPEIA signal is strongly correlated with the generated FWM light. Analytical and numerical calculations for the analysis of the relationship are presented.