Charge resolved electrostatic diagnostic of colliding copper laser plasma plumes Phys. Plasmas 18, 103104 (2011) Electron density measurement of inductively coupled plasmas by terahertz time-domain spectroscopy (THz-TDS) J. Appl. Phys. 110, 073303 (2011) A synchronized emissive probe for time-resolved plasma potential measurements of pulsed discharges Rev. Sci. Instrum. 82, 093505 (2011) Electrical time resolved metrology of dust particles growing in low pressure cold plasmas Phys. Plasmas 18, 093701 (2011) Additional information on Appl. Phys. Lett.

As collisions between electrons and neutral particles constitute one of the most representative physical phenomena in weakly ionized plasma, the electron-neutral (e-n) collision frequency is a very important plasma parameter as regards understanding the physics of this material. In this paper, we measured the e-n collision frequency in the plasma using a calibrated cutoff-probe. A highly accurate reactance spectrum of the plasma/cutoff-probe system, which is expected based on previous cutoff-probe circuit simulations [Kim et al., Appl. Phys. Lett. 99, 131502 (2011)], is obtained using the calibrated cutoff-probe method, and the e-n collision frequency is calculated based on the cutoff-probe circuit model together with the high-frequency conductance model. The measured e-n collision frequency (by the calibrated cutoff-probe method) is compared and analyzed with that obtained using a Langmuir probe, with the latter being calculated from the measured electron-energy distribution functions, in wide range of gas pressure.

This paper proposes a new measurement method of electron density using the reactance spectrum of the plasma in the cutoff probe system instead of the transmission spectrum. The highly accurate reactance spectrum of the plasma-cutoff probe system, as expected from previous circuit simulations [Kim et al., Appl. Phys. Lett. 99, 131502 (2011)], was measured using the full two-port error correction and automatic port extension methods of the network analyzer. The electron density can be obtained from the analysis of the measured reactance spectrum, based on circuit modeling. According to the circuit simulation results, the reactance cutoff probe can measure the electron density more precisely than the previous cutoff probe at low densities or at higher pressure. The obtained results for the electron density are presented and discussed for a wide range of experimental conditions, and this method is compared with previous methods (a cutoff probe using the transmission spectrum and a single Langmuir probe).

Wave-cutoff method using microwave provides capabilities for diagnostics of various processing plasmas, and can give the precise absolute electron densities 1 . In this study, pressure limitation of electron density measurement using a wavecutoff method is presented. As gas pressure increases, the wave-cutoff signal disappears. The disappearance of signal happens when the electron-neutral collision frequency is over the plasma frequency. At that time, the electron motion cannot catch up to the movement of the electromagnetic wave, and the electromagnetic waves begin to penetrate into plasma. In result, the wave-cutoff signal disappears.In this work, the pressure limitation of wave-cutoff method is shown by using an impedance analysis of the probe system, and using commercial microwave simulator, CST MicroWave Studio 2 .1. "Plasma frequency measurements for absolute plasma density by means of wave cutoff method", Appl. Phys. Lett. 83, 4725 (2003). 2. Website address : http://www.cst.com 978-1-4244-2636-2/09/$25.00 ©2009 IEEE

In this contribution we present the physics behind the cut off probe and discuss recent advancements for the practical implementation of this diagnostic technique in industrial settings.Introduced a decade ago as a precise technique for the measurement of the local plasma density in low pressure discharges, recent experimental and computational studies have advanced our understanding on the origin and interpretation of the measured electromagnetic spectrum.Amplitude and phase measurements, probe sensibility, operation in collisional regimes, probe geometry, sheath effects and chamber resonances have been investigated extensively recently and here we summarize the most significant findings 1-4 .Based on recent developments we also introduce a novel methodology to interpret the probe spectrum that eliminates the sheath and collisional effects and enables the use of this precise diagnostic technique in a broad range of practical processing conditions. 1.