Experimental and analytical evaluation of the acoustic radiation of femtosecond laser plasma filament sound sources in air.

Plasma filaments in air induced by femtosecond laser pulses lead to the generation of strong shock waves. This letter presents a systematic study, both experimental and theoretical, of the acoustic radiation by femtosecond laser-generated filaments. A theoretical model is developed based on the experimental results and is used to evaluate the directivity of the filament's acoustic radiation within and beyond the audible frequency range. It is shown that the acoustic directivity of plasma filaments can be derived from the model of a weighted acoustic line source, consisting of elementary point sources with N-shaped excitation.