Figure 1

(a) Overview of experimental energy diagram. An 852 nm probe laser excites the cesium atoms from the ground state \(|6S_{1/2}, F=4\rangle\) to the intermediate state \(|6P_{3/2}, F'=5\rangle\), and a 509 nm coupling laser drives the atoms from the intermediate state to the Rydberg state \(|60D_{5/2}\rangle\). δ is the energy level shift induced by the external RF field according to the ac Stark effect, and \(\Gamma _{i}\) (\(i=2, 3\)) is the state \(|i\rangle \) decay rate. (b) Sketch of the experimental setup. A cylindrical vapor cell is embedded into the field-sensing enhancement resonator. The probe light (red) is counter-propagated and overlapped with a coupling light (green) through the optical aperture of the resonator and detected by a photodetector (PD). The LO and SIG fields are generated by two independent SGs that are phase synchronized. The LO signal is guided to the LO port of the resonator via a coaxial cable. An isolator is used between the LO SG and the resonator to absorb the reflected waves from the LO port. Meanwhile, the SIG field is radiated to the resonator through a horn antenna