Multi-Watt cavity for 266 nm light in vacuum

Intense coherent ultraviolet radiation is gaining increasing importance in advanced quantum technologies—from optical clocks and quantum computers to matter-wave interferometry—as well as in photochemistry, life sciences, semiconductor industry, and space applications. Since the preparation of multi-Watt light sources is still an open challenge for many ultraviolet wavelengths, resonant enhancement in a cavity is an attractive alternative. However, many experiments with atoms, molecules or nanoparticles require isolation in high vacuum where UV optics often show fast degradation. Here, we present stable performance of a cavity for 266 nm light with several Watt of intra-cavity power in high vacuum despite the presence of hydrocarbons. Comparing two sets of cavity mirrors indicates that this feat is connected to the micro-chemical environment at the topmost coating layer. Our study emphasizes the need for further developments in this direction to facilitate robust, compact, and high-performing devices employing UV radiation.