Laser Spectroscopic Diagnosis of Active Species in Atmospheric Discharge Plasma

Surface micro-discharge (SMD), one type of cold atmospheri c pressure plasmas (CAPS), promises a bright future for num erous applications spanning the fields of aerospace and biom edicine due to its desirable features. Significantly, the reactiv e chemical species are key enablers and responsible for the bi omedical effects. Of all the CAP sources under investigation, the SMD array configuration offers a large area discharge wit h a considerable discharge volume enhances the plasma unifo rmity and provides an alternative to atmospheric pressure pla sma array technologies. This work presents the transport beh avior investigation of OH as well as NO radicals in an atmos pheric pressure pulsed-modulated surface micro-discharge in helium. Laser-induced fluorescence is employed to measure t he time development of OH and NO radical density distributi on during the pulse duration and the inter-pulse period. It is s hown that convection caused by ion wind due to electro hydr odynamic force enhances and dominates the transport of OH radicals from the surface plasma layer to the afterglow region with a distance up to 8 mm away from the dielectric surface. Interestingly, after the plasma switches off, OH density decre ases quickly near the electrode but the downstream distributi on region keeps constant, showing that the impact of convecti on is still present during the post-discharge. Additionally, the propagation velocity of OH declines monotonously with time. The maximum value is estimated as 1.86 m/s during the first 1 ms when the plasma is on. The influence of power delivere d to plasma is investigated, and the results indicate that the O H density everywhere in the detection zone is directly proport ional to the applied power. However, the input power has no significant influence on the propagation velocity and delivery distance, suggesting that it is unrealistic to increase the deliv ery distance of reactive species by increasing the power deliv ered to plasma.