We use two continuous-wave (CW) laser beams of 780 nm and 515 nm to optically drive $^{ 85}$Rb atoms in a heated vapor cell to a low-lying Rydberg state 10D$_{ 5/2}$. We observe a collimated ultraviolet (UV) beam at 311 nm, corresponding to the transition frequency from the 11P$_{ 3/2}$ state to the 5S$_{ 1/2}$ state. This indicates the presence of a coherent four-wave mixing process, built up by two input laser fields as well as a terahertz (THz) radiation of 3.28 THz that is generated by amplified spontaneous emission between the 10D$_{ 5/2}$ and the 11P$_{ 3/2}$ 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.
Categories: physics.atom-ph