Cavity ringdown laser absorption spectroscopy of a radio frequency discharge

Abstract

Cavity ringdown spectroscopy is a direct absorption technique performed with laser sources that has higher sensitivity than many other absorption techniques. It measures the rate rather than the magnitude of absorption of a molecule in a high reflectance cavity. By scanning the laser over a range of frequencies, the absorption spectrum for the molecule can be determined. The goal of this thesis is to combine the cavity ringdown technique with an rf discharge, so as to study molecules such as free radicals, without the difficulties and uncertainties associated with the previously used laser optogalvanic technique. The sensitivity and applicability of the technique have been demonstrated by measuring a molecular band of the formyl radical (HCO) with an absorption sensitivity greater than 1 part in 10(6), and comparing it to that taken with laser optogalvanic spectroscopy.