Detection of Pressure Waves Emitted From Plasma Jets With Fibered Optical Wave Microphone in Gas and Liquid Phases

Irradiation of atmospheric plasma jets to liquid targets induces a stream of reactive oxygen or nitrogen radicals from the liquid surface to the bottom under limited conditions, including frequency of applied voltage, gas flow rate, and so on. Pressure waves can be considered to be one of possible forces that concern with the stream inside liquid targets, because we succeeded to detect pressure waves generated by plasma jets in air with a fibered optical wave microphone. The fibered optical wave microphone works based on Fraunhofer diffraction of laser for phase objects, having superior sensitivity compared with other conventional optical methods for the detection of refractive index changes. In this paper, the fibered optical wave microphone measurement was done in air to investigate the frequency properties of the generation of pressure waves from plasma jets. In addition, the detection of pressure waves inside distilled water was attempted.