Comparison of Terahertz time domain spectroscopy and laser Thomson scattering for electron density measurements in inductively coupled plasma discharges

Terahertz time domain spectroscopy (THz-TDS) has been successfully applied in the plasma electron density diagnosis and the validity of the measurement results has been verified by Langmuir probe and microwave interferometer. In this work, the plasma electron density in argon discharge with inductively coupled plasma (ICP) source was in-situ measured by THz-TDS approach and combined with LTS method, which was acknowledged as a one of the most accurate method to measure the electron density. The ICP discharge was operated in the H-mode using a RF (13.56 MHz) power supply at 350 W under different argon gas pressures (30–90 Pa). The results indicate that features of the electron density as a function of the argon pressures measured both by THz-TDS and LTS are good agreement and the deviation between THz-TDS and LTS is in the region from 13% to 24%. The results futher verify the application potential of the THz-TDS for non-invasive plasma electron density measurement.