Characterization of an atmospheric pressure plasma jet using optical emission and cavity ringdown spectroscopy

Cold plasma is useful in numerous medical applications, largely because of the highly-reactive chemical species generated in the discharge. The hydroxyl radical (OH) is of these species and has significant biological importance. An atmospheric pressure plasma jet (APPJ) was constructed in the form of a plasma pencil, and relative and absolute measurements were made of OH in both its first excited ground state--OH(A) and OH(X), respectively--using optical emission spectroscopy and cavity ring-down spectroscopy (CRDS). The total number of OH radicals were found to be constant in the plume and within the range given by relative measurements made on similar devices in the literature.