Detection of HO₂in an atmospheric pressure plasma jet using optical feedback cavity-enhanced absorption spectroscopy

Abstract

Cold non-equilibrium atmospheric pressure plasma jets are increasingly applied in material processing and plasma medicine. However, their small dimensions make diagnosing the fluxes of generated species a challenge. Here we report on the detection of the hydroperoxyl radical, HO _2 , in the effluent of a plasma jet by the use of optical feedback cavity-enhanced absorption spectroscopy. The spectrometer has a minimum detectable absorption coefficient ${\alpha }_{\min }$ of $2.25\times {10}^{-10}$ cm ^−1 with a 100 second acquisition, equivalent to $5.5\times {10}^{12}\ {\mathrm{cm}}^{-3}$ of HO _2 (under ideal conditions). Concentrations in the range of (3.1–7.8) × 10 ^13 cm ^−3 were inferred in the 4 mm wide effluent of the plasma jet.