Laser frequency locking based on Rydberg electromagnetically induced transparency

We present a laser frequency locking to Rydberg transition with electromagnetically induced transparency (EIT) spectra in a room-temperature cesium vapor cell. Cesium levels 6S_1/2, 6P_3/2, and the nD_5/2 state, compose a cascade three-level system, where a coupling laser drives Rydberg transition, and probe laser detects the EIT signal. The error signal, obtained by demodulating the EIT signal, is used to lock the coupling laser frequency to Rydberg transition. The laser frequency fluctuation, ~0.7 MHz, is obtained after locking on, with the minimum Allan variance to be 8.9× 10^-11. This kind of locking method can be used to stabilize the laser frequency to the excited transition.