A low-duty cycle UV laser for spectroscopy on a beam of AlCl

AlCl is a very promising candidate for direct laser cooling and trapping. Given its highly diagonal Frank-Condon factor (99.88%) and high scattering rates, it is expected that starting with a cryogenic buffer-gas beam of AlCl, only a few (potentially ~3) lasers are required to slow the molecules to a complete stop. One of the major challenges of this experiment is that the laser transitions are in the deep UV at 261 and 265 nm. While laser systems that provide high powers of up to 1W at these wavelengths have been built, operating experiments that use deep UV wavelengths comes with additional challenges. In particular, the degradation of optics can be a major obstacle for running experiments for longer times.

Here, we present our approach to carry out spectroscopy on a cryogenic buffer-gas beam of AlCl using 261nm light, while avoiding UV damage by minimizing the duty cycle of the used light. Specifically, we produce 261nm light by frequency doubling a solid-state 523nm laser in a SHG cavity. To minimize the duty cycle of the UV light, we ramp the cavity into resonance shortly before each experimental cycle and move the cavity off-resonant after the molecules have crossed the laser beam. Using this approach, we are able to operate our UV laser system over long periods of time without significant degradation and carry out spectroscopic studies on AlCl.