(a) Schematic diagram of the experiment. The coupling (λ_c = 510 nm) and probe (λ_p = 852 nm) beams counter-propagate through a cesium vapor cell along the y-axis. The horn placed 86 cm from the cell (not scaled) emits an RF electric field with a frequency ∼15.21 GHz for coupling the Rydberg transition and producing an EIT-AT spectrum. The horn is set such that the RF electric field is linearly polarized along the z-axis which is parallel to the polarizations of the probe and coupling laser beams. The probe beam passing through a cesium cell and a dichroic mirror is detected with a photodiode. The PBS indicates polarization beam splitter. (b) The energy level diagram of the cesium four-level system. The probe laser λ_p is resonant with the ∣ 6 S 1 / 2 F = 4 〉 → ∣ 6 P 3 / 2 F ′ = 5 〉 lower transition, and the coupling laser λ_c is scanned through the ∣ 6 P 3 / 2 F ′ = 5 〉 → ∣ 66 S 1 / 2 〉 Rydberg transitions. The applied RF electric field couples the transition ∣ 66 S 1 / 2 〉 → ∣ 65 P 1 / 2 〉 , yielding a Rydberg EIT-AT spectrum.