Accurate Optical Number Density Measurement of CO212 and CO2

Direct Comb Vernier Spectroscopy for Fractional Isotopic Ratio Determinations

“…Such measurements can be used to determine sources, skins and mechanisms of formation of this potent greenhouse gas and ozone-depleting agent, helping to improve current mitigation strategies. Similarly, accurate optical number density of 12 C and 13 C single substituted isotopic variants of C 16 O 2 gas with a precision of, respectively, 0.03% and 1.24%, were measured by using DFCDS in the near-IR [25]. These kinds of measurements open the way for environmental monitoring and biomedical sciences applications of this OFC-based technology.…”

“…determination is strongly limited by these experimental issues, which must be avoided to obtain the determinations for this isotope that are comparable to those achieved in other DFCDS [25]. Measurements at lower pressures could avoid saturation effects for this transition, paying for a decrease in the S/N ratio of the 13 C 16 O 2 transition by considering that the gas sample and absorption path are shared for both transitions.…”

“…According to the type of application, the desirable target for accuracy and precision in such measurements could be different. For example, in very demanding biomedical applications (i.e., breath test for disease diagnosis or metabolic status monitoring), the accuracy and precision level for the R13 C/ 12 C isotopic ratio could be lower than 0.5% [24,25] Broadband spectroscopic techniques that use optical frequency combs (OFC) as an interaction laser source have become very popular for multiplexed detection of molecular species. Among all molecular parameters measurable with such techniques, the accurate determination of the isotopic composition of a gas sample is surely one of the most challenging applications.…”

“…OFC-based spectroscopic techniques with dual comb [26], Fourier transform [27] and spatially dispersive [28][29][30][31] detection schemes, sometimes combined with Fabry-Perot enhanced spectroscopy [29][30][31][32], are widely used for trace gas detection [19,30,31,[33][34][35][36][37]. However, the most accurate results regarding fractional isotopic ratio measurements were obtained by direct frequency comb dispersive spectroscopy (DFCDS) [25,38]. Bailey and coworkers [38] used a MIR-FC-based cross-dispersed spectrometer to measure a fractional isotopic abundance of nitrous oxide (N 2 O) with a precision of 6.7 × 10 −6 in 1 s of acquisition time.…”

Precision Spectroscopy of Nitrous Oxide Isotopocules with a Cross-Dispersed Spectrometer and a Mid-Infrared Frequency Comb

“…Comb-based spatially dispersive spectrometers have the sensitivity to enable the study of reaction kinetics critical to understanding atmospheric processes, , but can be limited in terms of absolute accuracy when comb teeth are unresolved. Challenges in retrieving accurate optical frequency assignments and corresponding transmission through a gas sample are often attributed to a complex instrument function. ,− To elevate these spectrometers for use in high-resolution spectroscopy, rigorous evaluation of the instrument function along with spectral reconstruction independent of reference databases are required. Here, we present an instrument for precision spectroscopy of N 2 O using an optical frequency comb centered near 4.5 μm (2222 cm –1 ) coupled to a cross-dispersed spectrometer using a virtually imaged phased array (VIPA) and ruled diffraction grating.…”