Investigation of Inductively-Coupled Plasma Density by Comparing the THz Waveforms in the Time Domain

In the THz-based plasma diagnostics, plasma information can be deduced via measurement of the THz phase shift in the frequency domain. However, little study has been reported on how THz waveforms in the time domain can be used for plasma diagnostics. Hence, we performed studies on the time-domain THz waveforms from the calculation through the plasma model and compared them with the experimental result. For this experiment, intense THz pulses were generated by focusing two-color femto-second (fs) laser pulses in air and they were sent through an inductively-coupled argon plasma source which was powered by RF with a frequency of 13.56 MHz. The comparison results show that the waveform comparison method (plasma model) in the time domain can provide the electron density information successfully, implying that the plasma density diagnostic method based on the waveform comparison works properly. Furthermore, the collision frequency data from our experiment reveals that the plasma model should include more factors to describe the observed phenomena.