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. In warm vapors, Doppler-free alignments leading to zero-velocity spin waves or expanded velocity class inclusion are possible with three-photon EIT but require further experimental investigation. We present experiments in warm vapors using an all-infrared scheme and discuss prospects for electric field sensing and exploring interactions between thermal Rydberg atoms.