Collimated UV light generation by two-photon excitation to a Rydberg state in Rb vapor

We use two continuous-wave laser beams of 780 nm and 515 nm to optically drive Rb85 atoms in a heated vapor cell to a low-lying Rydberg state 10D5/2. We observe a collimated ultraviolet (UV) beam at 311 nm, corresponding to the transition frequency from the 11P3/2 state to the 5S1/2 state. This indicates the presence of a coherent four-wave mixing process, built up by two input laser fields as well as terahertz (THz) radiation of 3.28 THz, which is generated by amplified spontaneous emission between the 10D5/2 and 11P3/2 states. We characterize the 311 nm UV light generation and its dependence on various physical parameters. This scheme could open up a new possibility for generating narrow-band THz waves as well as deep UV radiation