Near-surface reduction of cavity ring-down spectroscopy detection sensitivity

Cavity ring-down spectroscopy (CRDS) is a high-sensitivity technique used t o measure the absolute concentrations of absorbing species. We have used CR DS to measure spatially dependent concentration profiles near a physical su rface that obstructs the light path. A decrease in detection sensitivity re sulting from interaction between the circulating cavity ring-down beam and the surface was observed. Simple calculations based on geometrical obstruct ion by the solid surface significantly underestimate the sensitivity loss, suggesting that diffraction is important. Calculations that include diffrac tion effects more closely agree with experimental data. (C) 2000 Published by Elsevier Science B.V. All rights reserved.