Development and implementation of acoustic diagnostics to measure plasma energy deposition from a laser plasma generated in air

The absorbed energy from a short pulse laser produced plasma is proportional to the magnitude of the acoustic wave the plasma launches; however, methods to resolve absolute energy from the acoustic signal are still being developed. This is the first report of quantitatively estimating the energy deposited by a femtosecond laser-induced plasma using a shock wave approximation from acoustic measurements. To further understand energy deposition mechanisms, two diagnostics, a single microphone which measures the acoustic signal propagation and an array of microphones which measure the changing acoustic signal longitudinally along the plasma were developed and implemented to measure the energy absorbed. A weak shock wave approximation model is used to fit results from the acoustic measurements to yield a quantitative energy deposition estimation. 2D Unidirectional Pulse Propagation Equation (UPPE) simulations show general agreement in experimental longitudinal energy deposition profile results and absolute total energy deposition values. These results will help to further understand the relationship between the dynamics of a laser-induced plasma and weak, broadband microwave frequencies known to radiate from them.

DISTRIBUTION A: Approved for public release; distribution is unlimited. Public Affairs release approval #AFRL20232760