On the correlation of light and sound radiation following laser-induced breakdown in air

Laser-induced breakdown in ambient air by short optical pulses is accompanied by light and sound emission from the excited volume. In this work, these secondary radiative phenomena are jointly studied and their correlation is analyzed and demonstrated both experimentally and analytically. Simultaneous systematic measurements of the light and acoustic signals produced by nanosecond laser pulses of different energies are presented at sufficiently large time windows that allow for the observation of the complete phenomena. The contribution originating from the raised temperature (thermal radiation) in the excited volume is isolated out of the full optical signal and reconstructed via signal processing techniques. Through this analysis it becomes evident that the thermal radiation and the acoustic radiation take place at the same time scales. Moreover, the thermal radiation signal is used as a source in a theoretical model to estimate the frequency spectra of the generated acoustic pulses. The model's evaluations show very good agreement with the experimental measurements of the laser-induced breakdown acoustic spectra for different laser pulse energies. The presented method demonstrates experimentally and analytically the correlation between light and sound radiation following laser-induced breakdown in the ambient air and proves that the emitted sound pulses can be directly evaluated from the respective optical signal.