Mid-IR frequency comb cavity ringdown to simultaneously measure weakest and strongest absorption features over ultra-broadband coverage (Conference Presentation)

When measuring molecular contents in a gas sample, strong absorptions from species such as water vapor and carbon dioxide can impose a strong background. This hinders robust detection of molecular species present at the lowest possible concentrations. Here we present Modulated Ringdown Comb Interferometry, a new technique that enables detection of the weakest absorption features on top of the strongest for unprocessed gas samples. We demonstrate with an instrument that can highly effectively measure over 1,000 cm-1 mid infrared spectral coverage, over 4 km effective absorption path length, and at rotational-vibrational quantum state resolution. Up to 20 distinct species in exhaled human breath and ambient air are quantified simultaneously down to > 1 parts-per-trillion detection sensitivity at highly efficient, near fully-automated settings.