Ultra fast and sensitive electron density measurement by THz time domain spectroscopy
Final Report Abstract
The aim of the project was to further develop terahertz time-domain spectroscopy (THz-TDS) as a method of plasma diagnostics. The method is basically similar to the classical microwave interferometry. However, THz of very short duration of only a few ps are used here. This short pulse length is associated with a high temporal resolution on the one hand and measurement over a broad frequency band on the other hand. Furthermore, the temporal development of the field is measured directly, i.e. determination of the field’s amplitude and phase. The short pulse duration makes the method insensitive to mechanical oscillations, one of the central problems of classical interferometry. In addition, the broad frequency spectrum allows the dispersion relation to be fitted over a wide spectral range, which avoids further problems of ambiguity of the classical interferometry. The starting point of the project was a commercial THz system, which, however, had to be modified in essential points. In particular, the emitter antenna was replaced and the entire detection principle was converted to electro-optical detection. The use of a modern lock-in amplifier and its integrated dual-frequency multichannel boxcar option (DFMB) allows a variable time resolution of up to 100 - 200 ps. The new diagnostics is initially demonstrated by determining the plasma density in stationary noble gas discharges (He, Ne, Ar, Kr, Xe) as well as pulsed Ar and Ne discharges in a magnetic multi-cusp discharge chamber. Further, benchmark tests comparing the THz-TDS with the classical microwave interferometry shows very good agreement. Finally, the method allows for the first time time-resolved measurements of the electron density in the magnetic confinement region of a HiPIMS discharge.
Publications
-
Measurement of plasma densities by dual frequency multichannel boxcar THz time domain spectroscopy. Journal of Physics D: Applied Physics, 50(24), 245202.
Meier, St M; Tsankov, Ts V; Luggenhölscher, D & Czarnetzki, U
-
First measurements of the temporal evolution of the plasma density in HiPIMS discharges using THz time domain spectroscopy. Plasma Sources Science and Technology, 27(3), 035006.
Meier, Steffen M; Hecimovic, Ante; Tsankov, Tsanko V; Luggenhölscher, Dirk & Czarnetzki, Uwe
-
Plasmadichtebestimmung mittels Dual-Frequency-Multichannel-Boxcar-THz-Time-Domain-Spektroskopie. Diss. RUB, 2018
Meier, Steffen Marius
