Exploring electron density and terahertz polarization characteristics in inductively coupled plasmas by terahertz spectroscopy and polarimetry

As a noninvasive optical method, terahertz time-domain spectroscopy (THz-TDS) has been applied to diagnose the plasma parameters. Previous reports mainly focused on the phase and amplitude changes of THz waves induced by the plasma, while the terahertz polarization characteristics were rarely reported. In this paper, in addition to the plasma electron density and terahertz transmittance, we further applied the terahertz time-domain polarimetry (THz-TDP) method to diagnose the terahertz polarization rotation angles induced by an argon inductively coupled plasma (ICP). The experiment results and theoretical analysis further extend the ability of terahertz techniques for plasma diagnostics and show that the gas plasma-like ICP has the potential to become a tunable THz modulator.