Four-level, all infrared, Doppler-free Rydberg EIT in rubidium

Four-level, three-photon ladder Rydberg EIT has several potential advantages over the more popular two-photon Rydberg EIT in its applications to field sensing and non-classical photon state generation. For example, in warm vapors, Doppler-free alignments leading to zero-velocity spin waves or expanded velocity class inclusion are possible with three-photon EIT. We present experiments in warm vapors using an all-infrared scheme which include collinear configurations of the incoming lasers and a Doppler-free configuration where the incoming beams’ wavevectors sum vectorially to zero. We show that numerical simulations match the qualitative features of the experimental configurations and that there are regimes where the Doppler-free configuration may lead to improved sensitivity over collinear configurations.