High-Speed Imaging And Temperature Measurements Of Microwave Enhanced Laser Induced Plasma

Abstract

Air plasma is typically generated by laser-induced breakdown using a focused high-energy laser beam. In microwaveenhanced laser-induced plasmas, the initial spark produced by laser-induced ablation of a nearby target may be utilized to generate air plasma by microwaves. Air plasma was therefore produced with and without a nearby target. Characterization of the air plasma was done by high speed-imaging and time-series emission spectral measurements. The evolution of the plasma temperature was measured by SPECAIR simulations of the OH and N2+ positive systems. The microwave-enhanced plasma exhibit unequal values for the vibrational and rotational temperatures indicating a nonequilibrium state of the air plasma. The estimated temperatures of vibrational temperatures were considered lower estimates of the electron temperature and rotational temperatures as higher estimates of the gas temperature. The increase in vibrational temperatures of the air plasma with and without the target both indicated the heating of the electrons due to the addition of microwaves. However, the constant value of the rotational temperature for both cases indicated that the gas temperature is not affected by the microwave.