Total line intensity of metal lines per 45 nm in VIS setup. Blue bars represent the total line intensity per spectral range of U lines and red represents Th lines. Magenta indicates the overlap areas. The spectral region between the dashed lines (from 610 to 655 nm) indicates where the internal laser of our FTS contaminates the recorded spectra. Upper panel: HCLs with Ar buffer gas (U–Ar and Th–Ar). Bottom panel: HCLs with Ne buffer gas (U–Ne and Th–Ne).