Low-Duty-Cycle Pulsed UV Technique for Measuring Isotope Shifts in Aluminum Monochloride

Laser technology enables advancing frontier research, particularly in the direct laser cooling of molecules, which often requires multiple laser systems. While robust, tunable continuous-wave (CW) laser systems are readily available across the visible and infrared spectrum, developing such systems in the deep ultraviolet (UV) range poses significant technical challenges. A major difficulty arises from deep-UV radiation degrading and damaging materials, including the non-linear crystals used for higher-harmonic generation. These crystals are hygroscopic and susceptible to UV-induced damage, limiting the longevity of experimental setups.

To address this, we developed a technique for spectroscopy on a cryogenic buffer-gas beam of AlCl using 261 nm light while minimizing UV exposure of any involved optics. Specifically, the 261 nm light is generated by frequency doubling a 523 nm laser in a second-harmonic generation (SHG) cavity. To reduce UV-induced damage, we ramp the cavity into resonance briefly before each experimental cycle and shift it off-resonance immediately afterward. This reduces the UV duty cycle to ~5%, allowing long-term measurement of isotope shifts of the electronic transition (X¹Σ ← A¹Π) in AlCl at 261.5 nm without significant degradation (Opt. Express 32, 32977-32990 (2024)).