  A velocity-selective spectroscopy technique for studying the spectra from hot
Rydberg gases is presented. This method provides high-resolution measurement of
the spectrum interval. Based on this method, the velocity-selective hyperfine
splitting of intermediate states is measured, as well as the Doppler-free
fine-structure splitting of the Rydberg states via two-photon Rydberg
excitation in a room-temperature 133Cs vapor cell. The experiment data and
theoretical predictions show excellent agreement.
