Two species-one wavelength detection based on selective optical saturation spectroscopy.

Cross-sensitivity limits accurate quantitative detection of species concentrations in all sensor technologies, including laser-based absorption techniques. Absorption sensors capture a signal that combines contributions from all interfering species at a given detection wavelength. Careful selection of the probed spectral line, broadband detection, or upstream separation can partially mitigate cross-sensitivity, however, weak or unidentified signal interference remains a challenge for accuracy. Here, we present a proof-of-principle study to overcome cross-sensitivity by taking advantage of the distinct optical saturation characteristics of different gas mixture components. By controlling the absorption contribution of a selected species by intentional optical saturation, simultaneous and quantitative detection of two interfering species becomes possible even without the need for spectral scanning, hence offering two species-one wavelength detection (2S1W) capability. Demonstrated with direct absorption and cavity-ringdown setups, the method offers a new, previously unexploited opportunity to further enhance laser-based analyzers for complex gas mixture analysis in environmental, medical, and technical applications.