Direct frequency comb saturation spectroscopy with an ultradense tooth spacing of 100 Hz

Abstract

Electro-optic frequency combs with tooth spacings as low as 100 Hz were employed to probe electromagnetically induced transparency (EIT) and hyperfine pumping in rubidium and potassium vapor cells. From the potassium EIT transition we were able to determine the ground state hyperfine splitting with a fit uncertainty of 8 Hz. Importantly, because of the mutual coherence between the control and probe beams, which originate from a single laser, features with linewidths several orders-of-magnitude narrower than the laser linewidth could be observed in a multiplexed fashion. This approach removes the need for slow scanning of either a single laser or a traditional mode-locked-laser-based optical frequency comb.