Terahertz time-domain spectroscopy as a new tool for the characterization of dust forming plasmas

We report the application of terahertz time-domain spectroscopy as a new tool for plasma diagnostics. The short broadband THz pulses were radiated from a low temperature grown GaAs emitter by free charge carriers which were generated by focusing a 20 femtosecond TiSa-laser pulse onto the emitter. For sensitive signal recording a coherent detection scheme was applied. This allowed the measurement of the amplitude and sign of the electromagnetic field of the THz pulse after passing the plasma chamber. Fourier transformation allowed us to obtain the full spectrum in the frequency domain. We compared the transmitted THz, intensities of a pure argon (Ar) and an acetylene (C2H2)/argon plasma. The presence of the ethynyl-radical (CCH) andcyclopropenylidene (C-C3H2) in the (C2H2)/argon plasma could be confirmed by the observations of rotational transitions in the region from 8 to 16 cm(-1) corresponding to 0.3-0.5 THz.