Microwave field sensing and laser stabilization with Rydberg atoms excited through the 7 <i>P</i> 1/2 state in an inverted ladder scheme

We present an inverted ladder cesium Rydberg atom excitation scheme with a probe transition of 6S1/2→7P1/2 (459 nm) and coupling transition of 7P1/2→nD3/2 (⩾1038 nm) for electric field sensing, as an alternative to schemes that use the D1 and D2 probe laser transitions and green light coupling laser transitions. We investigate the transition from enhanced absorption (EA) to electromagnetically induced transparency for different probe Rabi frequencies and conduct experiments to validate Autler–Townes splitting of the nD3/2→(n+1)P1/2 and nD3/2→(n−2)F5/2 Rydberg transitions in the presence of on-resonance microwave fields, for a proof-of-concept demonstration of microwave field sensing using EA in an inverted ladder scheme. Finally, we demonstrate 459 nm probe laser stabilization to the hyperfine lines in a saturated absorption spectroscopy configuration, and laser stabilization of the 1038 nm coupling laser to an EA spectral feature in a counter-propagating probe and coupling laser configuration. Under stabilization, Allan deviations of less than 200 kHz for τ&amp;lt; 50 s are achieved for both the probe and coupling lasers.