Frequency-stabilized cavity ring-down spectroscopy

We describe frequency-stabilized cavity ring-down spectroscopy (FS-CRDS), an ultraprecise refinement of conventional CRDS. We review the technique and highlight some recent studies that have utilized FS-CRDS to perform precision measurements of molecular transitions in the near-infrared. We describe system enhancements that are currently under implementation, including Pound–Drever–Hall locking and optical frequency comb-stabilization, which have the potential to reduce the uncertainty in both the absorption and frequency axes of our spectra by more than an order of magnitude. Finally, we describe high impact applications of this capability that can exploit frequency axis uncertainty at the 10 kHz level and signal-to-noise ratios exceeding 200 000:1.