Acoustic Diagnostics of Femtosecond Laser Filamentation

The promising application of femtosecond laser filamentation in atmospheric remote sensing brings imperative demand for diagnosing the spatiotemporal dynamics of filamentation. Acoustic emission (AE) during filamentation opens the door to giving insight into the dynamic evolution of filaments in air. In particular, the frequency features of the acoustic emission provide relevant information on the conversion of laser energy to acoustic energy. The acoustic emission of femtosecond laser filament manipulated by laser pulse energy and focal lengths was measured quantitatively using a broadband microphone. The experimental results showed that the acoustic power W presents a squared dependence on the laser pulse energy ${E}$ , i.e. W proportional to E-2 . The spectral bandwidth of the acoustic pulse emitted from the optical filament is found to be an indicator of the filament intensity distribution, which is positively correlated with the laser filament intensity. These findings are helpful for studying the plasma filament properties and complex dynamic processes through acoustic diagnostics and benefit the remote applications of laser filament.