Velocity-selective spectroscopy measurements of Rydberg fine structure states in a hot vapor cell

A velocity-selective spectroscopy technique for studying the spectra of Rydberg gases is presented. This method provides high-resolution spectrum measurements. We present experimental results for a ladder system 6S_1/2→6P_3/2→nS(D) electromagnetically-induced transparency involving highly-excited Rydberg states. Based on a radio-frequency modulation technique, we measure the hyperfine structure splitting of intermediate states and the fine structure splitting of Rydberg states in a room temperature ¹³³Cs vapor cell. The experimental data and theoretical predictions show excellent agreement.