The Effect of Geometry on the Acoustic Radiation of Plasma Filaments in Air

Abstract : Laser-generated plasma filaments in ambient air generate acoustic pulses with characteristic emission directivity and frequency spectra. This work studies the effect of the geometrical characteristics of the plasma channel on the generated acoustic radiation. For this purpose, a model based on the classical line source is adopted, which deploys the correlation between light and sound following laser breakdown to predict the acoustic radiation of filaments in air. Through the model, the acoustic directivity and frequency spectra of plasma filaments with different lengths and plasma density distributions are studied. Preliminary results from acoustic measurements of the filament’s sound radiation are presented in the frequency domain. Finally, a complete model based on the wave equation with a heat source is outlined, which allows for the estimation of the filament’s acoustic radiation in the time and frequency domain at any point in space. Preliminary results from a computational simulation of a scaled model of a plasma channel are also shown, indicating that such a model can predict the directivity and spectral characteristics of filament sound sources.