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P: Plasmaphysik

P 9: Dense Plasmas and Plasma Diagnostic (Poster Session)

P 9.21: Poster

Tuesday, April 3, 2001, 12:30–15:00, AT2

Laser spectroscopic measurement of electric field strengths by means of optical impedance — •Steffen Franke, Samir Solyman und C. Wilke — Institut für Physik, Ernst-Moritz-Arndt-Universität Greifswald, Domstr. 10a, 17487 Greifswald

A method for measurements of even small electric field strengths with small perturbations of the plasma compared to probe measurements is investigated. Field strengths less than 10 V/cm are measured in a rare gas glow discharge with an accuracy of 20 %. The modulation of the discharge current of a low pressure glow discharge causes a frequency dependent, phase shifted modulation of the optical properties of the plasma. We call this effect optical impedance. Laser absorption spectroscopy enables one to evaluate the optical impedance quantitatively. For small current modulations time dependent rate equations of the current, the electron density as well as the excited state densities can be approximated by linear Taylor series. Combining the theory with the experimental results electric field strengths are determined. The range of validity of this method is restricted by the range of validity of the theory. The optical impedance method is suitable for measurements of small electric field strengths and for plasma regions with strong inhomogeneities, wherever Langmuir probes represent a large perturbation of the plasma or other methods fail due to small electric field strengths.