Acoustic diagnostics of femtosecond laser filamentation

TL;DR

This paper investigates the acoustic emissions from femtosecond laser filamentation in air, revealing how acoustic signals relate to filament dynamics and energy, aiding remote sensing and filament diagnostics.

Contribution

It provides a quantitative analysis of acoustic emissions during femtosecond laser filamentation, linking acoustic features to filament energy and spatial distribution.

Findings

Acoustic power scales quadratically with laser energy.

Acoustic spectrum bandwidth correlates with energy deposition.

Spectrum differences indicate filament intensity distribution.

Abstract

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 a door to give the 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. Here, the acoustic emission of femtosecond laser filament manipulated by energy and the focal lengths was measured quantitatively by a broadband microphone, and the acoustic parameters were compared and analyzed. Our results showed that the acoustic power presents a squared dependence on the laser energy and the bandwidth of the acoustic spectrum showed a significant positive correlation with laser energy deposition. It was found that the spectrum of the acoustic pulse emitted from the middle of the filament has a larger bandwidth compared to those emitted from the ends of the filament and the spectrum of the acoustic pulse is also an indicator of the filament intensity distribution. These findings are helpful for studying the plasma filament properties and complex dynamic processes through acoustic parameters and allow the optimization of remote applications.