Plasma and flow induced by single- and dual-pulse laser-induced breakdown in stationary air

The plasma and flow induced by laser-induced breakdown (LIB) were experimentally investigated in a stationary atmospheric air using deposited energy measurement, unfiltered plasma imaging, and high-speed schlieren imaging. Single- and dual-pulse LIB were studied to explore the effects of a laser pulsing strategy on the induced plasma and flow and their potential practical applications. For dual-pulsed LIB, various time intervals (50 ns, 150 ns, 40 mu s, and 100 mu s) and energy combinations (10-10, 20-20, 30-30, 30-10, and 10-30 mJ) were used to change the initial conditions for the second breakdown. Laser energy deposition, plasma generation, and hot plume generation were compared between SPLIB and DPLIB. For SPLIB, the plasma and flow were self-similar while the size of the plasma and flow increased with increasing laser energy. For DPLIB, the characteristics of the plasma and the flow (hot plume) and the laser energy deposition were strongly dictated by the time interval and energy combination. For a time interval of 150 ns, strong pulse-to-pulse coupling induced a second toroidal flow structure that suppressed third lobe generation. Depending on the time interval, the interactions between the hot plumes and shockwaves generated much finer flow structures compared to SPLIB. The uneven energy combinations (30-10 and 10-30 mJ) created coarser and finer flow structures, respectively, for relatively long time intervals (40 and 100 mu s) compared to the other energy combinations.