Measurement of 13C and 18O Ratio in CO2 using Quantum Cascade Laser based Tunable Absorption Spectroscopy

We present a spectroscopic approach for measurements of 13C and 18O isotopic ratio in carbon dioxide (CO2) gas using a quantum cascade laser (QCL). A narrow linewidth mid-infrared QCL is continuously scanned across three absorption lines of CO2 near 2310 cm-1 including 12C16O2, 13C16O2 and 16O12C18O isotopes. The simultaneous detection of three spectral lines permits the determination of simple concentration ratios (R13 and R18) in atmospheric CO2. With an averaging time of about 10 s both R13 and R18 reach a precision of 0.2 0 and 0.1 0, respectively.