In situ measurements of OH radicals in dielectric barrier discharge plasmas with cw-cavity ring-down spectroscopy

An apparatus of continuous wave cavity ring-down spectroscopy (cw-CRDS) has been constructed with the noise (RMS) equivalent absorption 3 × 10-9 cm-1. In situ quantitative measurements of OH radicals in dielectric barrier discharge (DBD) plasmas at low pressure using cw-CRDS are described. The influence of discharge voltage and pressure on number density of OH has been investigated. Results show that the OH production increases at low pressure with increasing discharge pressure; however, the number density of OH decreases due to electron attachment of H2O at higher pressure. The number density of OH radical increases with increasing discharge voltage and discharge frequency because of the increase of electron density and electron energy.