CLEO^®/Europe-EQEC 2023, Impurity-Free Gas Recycling System for an XUV Frequency Comb

Highly charged ions (HCIs) are promising candidates for measuring the variation of the natural constant $\alpha$ or realizing new frequency standards[1], thanks to their insensitivity to external electric fields and ultra-narrow fine-structure transitions. In HCIs, electronic transitions of the outer electron are shifted into the extreme ultraviolet (XUV), and even X-ray region. Lasers that can drive these transitions are not commercially available.