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

## TL;DR

This paper demonstrates the generation of collimated UV light at 311 nm through a four-wave mixing process in rubidium vapor, involving two-photon excitation to a Rydberg state and terahertz radiation emission, with potential applications in THz and UV sources.

## Contribution

It introduces a novel scheme for UV and THz wave generation using two-photon Rydberg excitation in rubidium vapor, with detailed characterization of the process.

## Key findings

- Successful generation of 311 nm UV light via four-wave mixing.
- Observation of terahertz radiation at 3.28 THz linked to Rydberg state transitions.
- Dependence of UV generation efficiency on physical parameters.

## Abstract

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.