Electron density measurements in pulsed atmospheric pressure air plasmas by IR heterodyne interferometry

Summary form only given. Microhollow cathode discharges have been shown to serve as plasma cathodes for atmospheric pressure air discharges. The high pressure discharges are operated dc at currents from 10 mA up to 30 mA and at average electric fields of 1.25 kV/cm. The electron density in the dc discharge was estimated to be in the range of 10/sup 12/ to 10/sup 13/ cm/sup -3/. In order to determine this value more accurately an interferometric technique has been used. Since sufficient spatial resolution requires the use of light sources with wavelengths on the order and preferable less than the characteristic dimension of the micro plasma (100 /spl mu/m) a CO/sub 2/ laser was used. At this wavelength (10.6 /spl mu/m) the index of refraction of atmospheric air plasmas with electron densities of 10/sup 13/ cm/sup -3/ is mainly determined by the heavy particles. In order to obtain information on the electron density, the discharge was operated in a pulsed repetitive mode with pulse duration varying between 100 ps and 50 ms.