Abstract

Cavity ringdown laser absorption spectroscopy (CRDS) is a sensitive, accurate way to acquire weak optical absorption spectra [1], Monochromatic light is multiply reflected within a high-finesse optical cavity containing the absorbing medium of interest and the energy loss rate (the inverse of ringdown time) is recorded. For sufficiently weak absorption, the ringdown rate increases linearly as absorbance of the medium. High-quality mirrors that are commercially available yield ringdown times of a few microseconds, resulting in a very long effective absorption path length for CRDS. Moreover, the ringdown time is usually independent of light intensity, so that sensitivity is not limited by optical intensity fluctuations, as is typical in most other forms of laser spectroscopy. These two features account for the high sensitivity (and rapidly expanding popularity) of CRDS [1].

© 2000 IEEE