Time-domain Ramsey-narrowed sub-kHz electromagnetically induced absorption in atomic potassium

The use of electromagnetically induced absorption (EIA) in sensing and metrology has been thus far hindered by saturation effects, which severely degrade its linewidth. Here we propose, and experimentally demonstrate, that time-dependent Ramsey spectroscopy in potassium vapour overcomes the detrimental effect of saturation. We observe sub-kHz Ramsey fringes, with full control of the EIA resonance characteristics. Combined with the efficient optical pumping associated to the K D-1 line, the present work demonstrates an EIA scheme suitable for sensing and metrological applications.