Detection sensitivity is often one of the most important attributes to
consider during selection of spectroscopic techniques. However, high
sensitivity alone is insufficient for spectroscopic measurements and peak
assignments in spectrally congested regions. Two-color cavity ringdown
spectroscopy (2C-CRDS), based on intra-cavity pump-probe detection,
simultaneously achieves high detection sensitivity, selectivity, and accuracy.
Thanks to its built-in compensation for instrumental baseline fluctuations and
one-photon background molecular signals, 2C-CRDS enables mid-IR detection of
radiocarbon dioxide (14CO2β) in room-temperature CO2β samples,
with better than 10 parts-per-quadrillion (ppq) measurement sensitivity and
accuracy (4 ppq on average from four separate trial measurements). This
detection capability is prohibitively challenging for other existing
spectroscopic techniques based on one-photon absorption, because of severe
spectral overlap between the very weak 14CO2β signals and the
orders-of-magnitude stronger hot-band signals from other CO2β isotopologues
at room temperature. 2C-CRDS measurements of room-temperature 14CO2β
samples at the record sub-10-ppq concentration level could directly benefit a
wide range of scientific fields that utilize 14C for dating and isotope
tracing, especially during field deployment. The 2C-CRDS technique
significantly enhances the sensitivity and general utility of high-resolution
mid-IR detection for analytical trace measurements and fundamental chemical
dynamics studies.Comment: 14 pages, 5 figures, 1 tabl