Hannover 2016 – scientific programme

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P: Fachverband Plasmaphysik

P 2: Plasma Diagnostics I

P 2.3: Talk

Monday, February 29, 2016, 11:55–12:10, b305

Dual frequency multichannel boxcar THz time domain spectroscopy measurements for the determination of the temporal evolution of the plasma density in pulsed low-pressure plasmas — •Steffen Marius Meier, Tsanko Vaskov Tsankov, Dirk Luggenhölscher, and Uwe Czarnetzki — Institut für Experimentalphysik V, Ruhr-Universität Bochum, 44780 Germany

THz time domain spectroscopy (THz TDS) is a non-invasive diagnostic method that allows the determination of the electron density and even the collision frequency. In contrast to microwave interferometry, THz TDS combines the advantages of a pico-second radiation pulse with a broad spectral width in the THz range ensuring better resistance to noise and vibrations. For the purpose of time-resolved measurements a standard THz TDS system was upgraded to improve the signal to noise ratio and the detection threshold. To achieve this, the detection method had to be changed. The lock-in frequency was increased from 7.6 kHz to 38 MHz to allow integration over more pulses within a shorter time. Additionally, a high performance lock-in amplifier is used that allows dual frequency multichannel boxcar measurements. Now measurements with less than 200 ps resolution are possible. The detection threshold was lowered to about 1 · 10¹¹ cm⁻³ or more precisely 1 · 10¹² cm⁻² line integrated.

The current status of the project as well as results from temporally resolved plasma density measurements in inductively coupled magnetic multi-cusp argon and neon low-pressure discharges are presented.