Swept-Cavity Ringdown Absorption Spectroscopy: Put Your Laser Light In and Shake It All About

Abstract

Cavity ringdown (CRD) absorption spectroscopy with continuous-wave (cw) tunable coherent light sources provides a convenient, sensitive, and precise way to measure very weak optical absorption spectra and to analyze trace gas concentrations. Several recently introduced innovations in cw-CRD spectroscopy are described. Our approach involves one or more single-mode tunable diode laser sources, a rapidly swept ringdown cavity, and a simple optical heterodyne detected approach (based on the dynamics of coherent light reflected from such an active optical cavity). This offers high performance in a relatively simple, low-cost, compact instrument that is facilitated by fibre optic and other standard photonics or telecommunications components. New experimental results are reported, comprising CRD spectra of water vapour in the 0.815 µm wavelength region and of mixtures of CO₂ and CO in the range of 1.56–1.59 µm. Promising applications of such techniques include chemical analysis of trace gases in medicine, agriculture, industry, and the environment.