Single-mode cavity ring-down spectroscopy for line shape measurements

The precise measurement of absorption line shapes and line strengths is demonstrated using single-mode cavity ring-down spectroscopy. This technique utilizes a pulsed laser to excite a single transverse electromagnetic mode of a high-finesse, stable resonator. From the measurement of the decay time constant of this mode, the optical losses can be determined. As the cavity mode is tuned through an absorption resonance, the variation of the decay rime constant yields a measure of the absorptive losses in the cavity. Spectra of the weak transitions of the molecular oxygen A-band are used to demonstrate the capability of this technique to measure absorption profiles and absolute line strengths. Repeated measurements of the line strength have a standard deviation <0.3 %.