Pulsed cavity ringdown laser absorption spectroscopy in a hollow waveguide

Cavity ringdown laser absorption spectroscopy (CRDS) is a modified version of standard absorption spectroscopy (AS) for providing extremely sensitive measurements of gas species absorbing at a particular wavelength in a gas cell volume. Typically, the enhancement in sensitivity with CRDS is a 10²-10³ improvement over AS. Herein, we analyze incorporating pulsed CRDS into a hollow-waveguide (HWG) both for reducing the sample volume as well as enhancing the signal-to-noise ratio (SNR) by up to ~10⁴ by injecting light into the HWG cavity through a small aperture in one of the cell mirrors. For low power instrument applications (i.e. planetary science), the enhancement in SNR results in a potential ~10⁴ reduction in laser power for a comparable CRDS terrestrial laboratory measurement at one extreme, or a potential ~10⁸ improvement in CRDS temporal resolution through reduced sample averaging with a fixed low-power laser source. A pulsed (vs. CW) laser source is employed to remove the requirement for a precision tuned laser cavity at ~wavelength spatial resolutions