Plasma diagnostic method using intermodulation frequencies in a Langmuir probe

A plasma diagnostic method using intermodulation frequencies is developed. When dual-frequency (ω1,ω2) voltage signals are applied to a probe, the intermodulation frequencies (ω2±ω1, ω2±2ω1) between the signals are generated due to the nonlinearity of the sheath. From the analysis of the intermodulation frequencies, the plasma parameters, such as the electron temperature and the plasma density, can be obtained. The measured plasma parameters from this method are compared to the results from the measured electron energy distribution function, and they are in good agreement. Because the intermodulation currents originated from the plasma not from the stray component of the measurement system, an accurate measurement of the plasma parameters is achievable