Mid-infrared quantitative spectroscopy by comb-referencing of a quantum-cascade-laser: Application to the CO2 spectrum at 4.3 μm

A robust phase-lock of a quantum-cascade-laser to a near-infrared frequency-comb allows absorption spectra of a CO2 gas sample to be acquired at different pressures with extreme repeatability and accuracy by tuning the repetition-rate of the comb, thus ensuring an absolute frequency scale on the acquired spectra. The method proves useful to retrieve traceable spectroscopic parameters such as line-center frequencies, line intensity factors, pressure shift, and pressure broadening coefficients, with unprecedented quality from the metrological point of view.