title: Very high finesse optical-feedback cavity-enhanced absorption spectrometer for low concentration water vapor isotope analyses.
abstract: So far, cavity-enhanced absorption spectroscopy (CEAS) has been based on optical cavities with a high finesse F that, however, has been limited by mirror reflectivity and by cavity transmission considerations to a few times 10,000. Here, we demonstrate a compact near-infrared optical-feedback CEAS instrument for water vapor isotope ratio measurements, with F>140,000. We show that this very high finesse can be effectively exploited to improve the detection sensitivity to the full extent predicted by the increased effective path length to reach a noise equivalent absorption sensitivity of 5.7×10(-11)  cm(-1) Hz(-1/2) for a full spectrum registration (including possible effects of interference fringes and fit model inadequacies).
authors.forename: J
authors.initials: J
authors.lastname: Landsberg
authors.forename: D
authors.initials: D
authors.lastname: Romanini
authors.forename: E
authors.initials: E
authors.lastname: Kerstel