Broadband photoacoustic spectroscopy of 14CH4 with a high-power mid-infrared optical frequency comb

We report a photoacoustic spectroscopy setup with a high-power mid-infrared frequency comb as the light source. The setup is used in broadband spectroscopy of radiocarbon methane. Owing to the high sensitivity of a cantilever-enhanced photoacoustic cell and the high-power light source, we can reach a detection limit below 100 ppb in a broadband measurement with a sample volume of only a few milliliters. The first infrared spectrum of ¹⁴CH₄ is reported and given a preliminary assignment. The results lay a foundation for the development of optical detection systems for radiocarbon methane.