Aachen PK 2003 – scientific programme

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P: Plasmaphysik

P 16: Plasma Diagnostics

P 16.6: Talk

Thursday, March 20, 2003, 17:10–17:30, FO2

Optical Time Modulation Spectroscopy in RF-Discharges — •Uwe Czarnetzki and Viktor A. Kadetov — Institut for Plasma and Atomic Physics, Faculty for Physics and Astronomy, Ruhr-University Bochum, 44780 Bochum

In RF-discharges, the time varying electric fields within the discharge cause a periodic modulation of the isotropic part of the electron energy distribution function. The modulation amplitude is proportional to the square of the electric field amplitude and increases with the electron energy. Highly excited states in atoms or molecules are excited by electrons in the tail of the distribution function where the modulation is particularly strong. Therefore, also the optical emission from these states is temporally modulated. Phase resolved detection of the emission and normalisation to the period average allows a simple and direct measurement of the modulation amplitude. If the measurement is performed also spatially resolved, one obtains a direct map of the relative electric field amplitude in the discharge. The complex conductivity of the plasma is linked to the field distribution by the Helmholtz equation. This allows in principle a direct determination of the plasma density distribution and the collision frequency without the need of a collision-radiative model. First measurements in an inductively coupled plasma in hydrogen where the Balmer-alpha line is observed are presented.