In the present work, two-photon absorption laser-induced fluorescence (TALIF) spectroscopy is used for the estimation of atomic nitrogen density in the ground state while optical emission spectroscopy is used to estimate the gas temperature from comparisons between experimental and synthetic OH (A-X) spectra. It can be found in for instance and the references given therein, many details on the laser-induced fluorescence spectroscopy and its advantages in comparison for instance to standard absorption or Raman spectroscopy. The alternative to obtain, for instance, the density of atomic nitrogen in the ground state, due to molecular nitrogen dissociation in the present microwave hot air plasma, is to use the absorption spectroscopy and more particularly the laser-induced fluorescence spectroscopy (LIF) that generally allows direct access to the density of the non-emissive species as atomic ground states and also metastables. However, OES cannot directly give any direct information on the non-emissive states as the density of the atomic ground state which can exceed the excited species density by several orders of magnitude in the case of the present microwave plasma. OES gives also information on for instance the temperatures of gas, rotation and vibration species from classical comparison between synthetic and experimental specific molecular spectra. In fact, OES allows the determination of absolute densities of the upper level of the emissive transition after a prior spectrum calibration using a spectral lamp. In our case, the experimental characterization to obtain more particularly the density of atomic nitrogen in such air plasma can be used, when coupled with previously obtained atomic oxygen densities, for validation of a complex hydro-kinetics model involving transport and plasma chemistry.Īs is known, the classical optical emission spectroscopy (OES) can give direct access only to the radiative excited species not to the ground state species. Many applications and understanding of plasma physics are expected from the characterization of the present hot air plasma. This work is devoted to the experimental determination of absolute density of atomic nitrogen in the background state (N 4S) coming from dissociation of molecular nitrogen of a hot air plasma generated by a microwave at 2.45 GHz resonant cavity for an input power of 1 kW. This is characteristic of the absence of chemical and energeticĮquilibria not yet reached in the air plasma column dominated by recombination Plasma column are lower than the cases where only thermodynamic equilibrium isĪssumed. The obtained dissociationĭegrees of molecular nitrogen in both dry and humid air plasma along the air Which is also larger for humid air plasma column. Of the measured absolute nitrogen density is also observed near the nozzle Partly due to attachment heating processes initiated by water vapor. Near the nozzle of resonant cavity on the axis of the plasma column. Humidity) are larger than those of dry air plasma column by practically 30% The rotational temperatures in humid air plasma column (50% of OpticalĮmission spectroscopy is considered to estimate the rotational gas temperatureīy adding a small amount of H 2 in dry air to better detect OH (A-X) in the same gas-conditioning cellīut without plasma) using an air gas mixture containing krypton. ![]() Calibration of TALIF signals is performed in situ ( i.e. Particularly performed along the radial and axial positions of the plasmaĬolumn. ![]() Density measurements based on laser inducedįluorescence spectroscopy with two-photon excitation (TALIF), are more Generated inside an upstream gas-conditioning cell at 600 mbar when the air gasįlow is directly injected at 10 slm in a microwave resonant cavity (2.45 GHz, 1 The determination of space-resolved absolute densities leads to obtain theĭissociation degrees of molecular nitrogen in the plasma. Measured in hot dry and humid air plasma columns under post-discharge regime. Densities of atomic nitrogen in its ground state ( N 4 S) have been
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