Opening fluorescence and four-wave mixing via dual electromagnetically induced transparency windows

We experimentally compare the probe transmission, four-wave mixing (FWM) and fluorescence signals under dressing effects for the first time. Especially, the interplay between two ladder subsystems is investigated in the Y -type atomic system. Moreover, the two-photon fluorescence signal with ultra-narrow linewidth is obtained, which is much narrower than the Doppler-free electromagnetically induced transparency window. Such fluorescence with very high coherence and monochromaticity can be potentially applied in metrology and quantum correlation.