Progress on a cryoprobe atom extraction and spectroscopy system for barium tagging in nEXO

The nEXO experiment is a planned search for 0$\nu \beta \beta $ decay using a liquid xenon time projection chamber. In order to reduce background, several methods for identifying (or ``tagging'') the daughter barium are being developed. One potential method of barium tagging being investigated involves freezing the potential barium in solid xenon and then extracting the frozen sample by using a cryoprobe system. Matrix isolation spectroscopic techniques would then be used to identify the single barium within the frozen sample.[1] Progress is presented here on the development and testing of a cryoprobe spectroscopy system at CSU for freezing solid xenon (SXe) from liquid xenon, creation of Ba$^{\mathrm{+}}$ ions by laser ablation of Ba metal and capturing them in SXe on a window on the cryoprobe and spectroscopy of the Ba atoms and ions in the SXe. [1] Mong et al. 2015