Gas temperature measurements in oxygen plasmas by high-resolution Two-Photon Absorption Laser-induced Fluorescence

• Published in: Journal of instrumentation 2015-11, Vol.10 (11), p.C11003-C11003
• Main Authors: Booth, J-P., Marinov, D., Foucher, M., Guaitella, O., Bresteau, D., Cabaret, L., Drag, C.
• Format: Article
• Language: English
• Subjects: Physics; Plasma Physics
• ISSN: 1748-0221; 1748-0221
• DOI: 10.1088/1748-0221/10/11/C11003

One of the most important, and difficult to measure, parameters of laboratory discharges in molecular gases is the gas translational temperature. We propose a novel technique to measure directly, with excellent spatial and temporal resolution, the velocity distribution of ground-state atoms (oxygen atoms in this case) in plasmas from the Doppler broadening of their laser excitation spectra. The method is based on the well-known Two-Photon Laser-induced Fluorescence (TALIF) technique, but uses a specially-built pulsed tunable ultraviolet laser with very narrow bandwidth which allows the Doppler profiles to be measured with high precision. This laser consists of a pulsed Nd:YAG-pumped Ti:Sapphire ring cavity which is injection-seeded by a single-mode cw Ti:sapphire laser. The single-mode infrared output pulses are frequency quadrupled by two non-linear crystals to reach the necessary UV wavelength (226 nm, 0.2 mJ) for TALIF excitation. This technique should be applicable to a wide range of discharges, ranging from low-pressure RF plasmas for surface processing to atmospheric pressure plasmas. Results of preliminary tests on low-pressure O 2 DC discharges are presented.