Time and spatially resolved electric field measurements by Stark polarization spectroscopy in a nanosecond pulsed atmospheric pressure helium jet operating in ambient air and impinging on a indium tin oxide coated glass slide are reported. An automatic fitting procedure of the Stark shifted spectra taking into consideration constraints regarding Stark components' positions and intensities as well as molecular nitrogen emission subtraction was implemented. This allowed electric field vector component measurements both in the gas phase and at the interface when the jet impinges on the substrate and during the development of a surface ionization wave. The obtained results show an increase in the axial electric field in the jet effluent in the gas phase with a peak magnitude from 12 to 18 kV cm-1 before the ionization wave impinges on the substrate. A steep electric field enhancement to a peak value of about 24 kV cm-1 was observed when the ionization wave impinges on the surface. A peak radial electric field of about 27 kV cm-1 was measured off-axis in the surface ionization wave. These results are consistent with previously reported modelling predictions. While Stark polarization spectroscopy is limited to electric field measurements from regions with emission, we illustrate that the capability to measure near surface electric fields in helium makes it a valuable complementary technique for the electric field-induced second harmonic (EFISH) technique.
Bibliographical noteFunding Information:
This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences under Award No. DE-SC0016053 and through the general Plasma Science Program (No. AT4010100). M.S.S. would like to thank Nikola Cvetanovic (University of Belgrade) for the fruitful discussions about the Stark polarization spectroscopy technique.
© 2020 Author(s).