Acoustic shock waves emitted from two interacting laser generated plasmas in air

We present an acoustic detection technique to study the interaction of two shock waves emitted by two nearby, simultaneous, laser-induced air-breakdown events that resembles the phenomenon of interaction of fluids. A microphone is employed to detect the acoustic shock wave (ASW) from the interaction zone. The experiments were done at various separation distances between the two plasma sources. The incident laser energy of the sources is varied from 25 to 100 mJ in ratios from 1:1 to 1:4. The peak sound pressure of the ASW was compared between the single and dual plasma sources, showing that the pressures are higher for the dual plasma source than that of the single plasma. The evolution of peak sound pressures is observed to depend on (a) the pulse energy of the sources and (b) the plasma separation distance, d. For the equal energy sources, the peak sound pressures increased linearly up to a certain plasma separation distance d, beyond which the pressures saturated and decayed. For the case of unequal energy sources, the peak sound pressures showed an interesting response of increase, saturation, decay, and further increase with plasma separation distance d. These observations indicate the dynamics of acoustic wave interactions across the interaction zone of the two sources depend on the input laser pulse energy as well as the plasma separation distance d.