Optical excitation of metastable noble gas atoms for atom trap trace analysis

Atom Trap Trace Analysis (ATTA) is a powerful technique that leverages the sensitivity and selectivity of laser cooling and trapping to measure abundances of trace radioisotopes. In particular, krypton ATTA is now routinely used to determine the residence time of groundwater and glacial ice across a broad timescale ranging from tens of thousands to millions of years. Yet one major limitation for noble gas ATTA is the need to excite atoms to a long-lived metastable state because laser cooling and trapping is not possible using the vacuum ultraviolet (VUV) transitions from the ground state. Current state-of-the-art ATTA devices produce metastable atoms through non-resonant excitation in a RF-driven plasma discharge. This method is not only inefficient (1 out of every 10,000 atoms is excited), but it also introduces cross-sample contamination via ion implantation in surfaces near the plasma. We report resonant optical excitation of metastable krypton and xenon beams utilizing a long-lifetime VUV-lamp and an infrared laser that outperforms a traditional RF-driven plasma source both in metastable excitation efficiency and overall maximum metastable flux. We also report progress toward a next-generation ATTA device that utilizes VUV lamp-based optical metastable excitation.