Acoustic characteristics of laser-induced plasmas from the forming dynamics perspective.

The acoustic signal has demonstrated its capabilities in assisting laser-induced breakdown spectroscopy (LIBS) measurements. In this study, the acoustic characteristics of laser-induced plasmas (LIPs) under different levels of energy deposition were analyzed, and their correlation with LIP forming dynamics was investigated. In the deposited energy space, two zones in the acoustic pressure and duration were observed, featuring a clear transition point in 100 mJ. The analysis based on self-emission spectra and images suggested that this transition is a result of the change in plasma forming dynamics. Above 100mJ, the plasma temperature and electron density were saturated; thus, any further increase in deposited energy only contributes to the plasma size. In this regime, the acoustic wave from the significantly elongated plasma no longer satisfied the ideal spherical assumption. The observation was also strengthened by the analysis in the frequency domain. Moreover, the correlation between acoustic and radiation signals was also changed significantly with plasma forming dynamics. This study offers a systematic analysis of LIP acoustic signals on the deposited energy space. The potential of using acoustic measurement to interpret the plasma forming dynamics was demonstrated, which could be beneficial for the successful implementations of acoustic-aided LIBS.