Cavity mode-dispersion spectroscopy applied in saturation conditions
Highly accurate molecular spectroscopy, apart from multiple applications in remote sensing, provides tools for tests of fundamental physics, such as quantum electrodynamics (QED) tests  and determination of physical constants variability . Transition frequencies can also be used as frequency standards for metrological applications if they are determined with sufficient accuracy .
Cavity mode-dispersion spectroscopy (CMDS)  of Doppler-broadened transitions has high accuracy in a wide dynamic range compared to cavity ring-down spectroscopy (CRDS) and cavity mode-width spectroscopy (CMWS) . In the present work, we demonstrate its application to Lamb-dip spectroscopy. The comparison with CRDS and CMWS again shows a predominance of the dispersive technique, which leads to the most accurate determination of the Lamb dip frequency. Neither CRDS nor CMWS is capable to show an evident absorption dip in the entire range of conditions covered by CMDS.
Here the CMDS technique is used to measure unperturbed frequencies and pressure shift of transitions from the 2nd overtone of CO near 1.57 μm. We determine line positions with sub-kHz accuracy. In contrast to the literature data , we detect non-zero pressure shift of transitions under investigation in saturation conditions.
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