Cavity-enhanced frequency up-conversion in rubidium vapour

TL;DR

This paper demonstrates that using a ring cavity with rubidium vapor enhances blue light power and narrows its linewidth via four-wave mixing, enabling applications like laser cooling and Bose-Einstein condensate production.

Contribution

The study introduces the first use of a ring cavity to simultaneously increase power and reduce linewidth of blue light generated by four-wave mixing in rubidium vapor.

Findings

Ring cavity enhances blue light power and narrows linewidth.

Linewidth achieved is less than 1 MHz.

Cavity tuning allows for application in laser cooling.

Abstract

We report the first use of a ring cavity to both enhance the output power and dramatically narrow the linewidth ($<1\,$MHz) of blue light generated by four wave mixing in a rubidium vapour cell. We find that the high output power available in our cavity-free system leads to power broadening of the generated blue light linewidth. Our ring cavity removes this limitation, allowing high output power and narrow linewidth to be achieved concurrently. As the cavity blue light is widely tunable over the $^{85}$Rb 5S$_{1/2} \,\,F=3$ $\rightarrow$ 6P$_{3/2}$ transition, this narrow linewidth light would be suitable for second-stage laser cooling, which could be valuable for efficient $^{85}$Rb BEC production.