Publication details

Measurement of the concetration of the OH radical in an atmospheric pressure plasma pencil by laser-induced fluorescence

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Year of publication 2013
Type Conference abstract
MU Faculty or unit

Faculty of Science

Description The concentration of radicals in reactive plasmas is an important parameter. The hydroxyl (OH) radical is known to be a strongly oxidizing species as well as an efficient source of UV radiation. Measuring the concentration of diatomic radicals at atmospheric pressure is a non-trivial task, especially in plasmas of small volume, such as the plasma pencil. One of the few methods suitable for this task is the laser-induced fluorescence, however, the interpretation of results at high pressures is difficult. We present a scheme suitable for measuring the concentration of the OH concentration in the flow of a rare gas mixing weakly with the ambient atmosphere. By exciting the ground vibrational state (v'=0) of the first excited electronic state (A2Sigma) we avoid the vibrational energy transfer (VET) in the laser-excited state. Together with the verified fact that the rotational energy transfer (RET) in the excited vibronic state is very fast, this justified using the very simple two-level model with (A2Sigma, v'=0) and (X2Pi,v''=0) vibronic states assumed to be in thermal rotational equilibrium during the whole process. The electronic quenching is taken into account by directly measuring the lifetime of the laser-excited state. The calibration is done by the Rayleigh scattering on air.
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