Electromagnetically induced transparency, absorption, and microwave-field sensing in a Rb vapor cell with a three-color all-infrared laser system

A comprehensive study of three-photon electromagnetically induced transparency (EIT) and absorption (EIA) on the rubidium cascade 5S1/2→5P3/2 (laser wavelength 780 nm), 5P3/2→5D5/2 (776 nm), and 5D5/2→28F7/2 (1260 nm) is performed. The 780-nm probe and 776-nm dressing beams are counteraligned through a Rb room-temperature vapor cell, and the 1260-nm coupler beam is co- or counteraligned with the probe beam. Several cases of EIT and EIA, measured over a range of detunings of the 776-nm beam, are studied. The observed phenomena are modeled by numerically solving the Lindblad equation, and the results are interpreted in terms of the probe-beam absorption behavior of velocity- and detuning-dependent dressed states. Interaction-time effects are discussed. To explore the utility of three-photon Rydberg EIA and EIT for microwave electric-field diagnostics, a sub-THz field generated by a signal source and a frequency quadrupler is applied to the Rb cell. The 100.633-GHz field resonantly drives the 28F7/2↔29D5/2 transition and causes Autler-Townes splittings in the Rydberg EIA and EIT spectra, which are measured and employed to characterize the performance of the microwave quadrupler.