  We demonstrate a single-photon Rydberg excitation spectroscopy of cesium (Cs)
atoms in a room-temperature vapor cell. Cs atoms are excited directly from
6S1/2 ground state to nP3/2 (n = 70 - 100) Rydberg states with a 318.6 nm
ultraviolet (UV) laser,and Rydberg excitation spectra are obtained by
transmission enhancement of a probe beam resonant to Cs 6S1/2, F = 4 - 6P3/2,
F' = 5 transition as partial population on F = 4 ground state are transferred
to Rydberg state .Analysis reveals that the observed spectra are
velocity-selective spectroscopy of Rydberg state, from which the amplitude and
linewidth influenced by lasers'Rabi frequency have been investigated. Fitting
to energies of Cs nP3/2 (n = 70 -100) states, the determined quantum defect is
3.56671(42). The demodulated spectra can also be employed as frequency
references to stabilize the UV laser frequency to specific Cs Rydberg
transition.
