Rayleigh Microwave Scattering for Diagnostics of Atmospheric-Pressure Microplasmas*

Conventional diagnostics cannot be used to measure plasma parameters of atmospheric pressure plasmas if plasma size is small (<1 mm) and density is low (<10¹³ cm⁻³). Microwave interferometry fails due to necessity to choose high testing frequency because of small plasma size, which leads to undetectable phase shift. Laser Thomson scattering has limited sensitivity for measuring plasmas with low ionization degree, namely minimal plasma ionization degree is about 10⁻⁶ (~10¹³ cm⁻³ for atmospheric pressure discharges), and it requires very significant accumulation of the signal (10⁵–10⁶ pulses) which is problematic in case of rapidly evolving non-reproducible plasmas.