Abstract

Cavity ring-down spectroscopy (CRDS) is a very sensitive, quantitative technique for measuring concentrations of weakly absorbing gas species. In CRDS, a high-finesse cavity is filled with radiation; the exciting radiation is then extinguished. The exponential decay time of the light leaking out of the cavity is measured, revealing the resonator losses, including those caused by absorbing species inside the cavity. Single-mode cw lasers (e.g., NPRO Nd:YAG or ECDLs) can be efficiently coupled into such cavities. Measuring the ring-down time as the laser is tuned reveals a high-resolution spectrum of any absorbing species. Typical absorption sensitivities are below 10⁻⁹ cm⁻¹.

© 1998 Optical Society of America