Suppression, enhancement, and reversal of hydrodynamic ejections by dual-pulse laser-induced breakdowns

A focused laser can cause optical breakdown of a gas, forming a plasma kernel that expands rapidly and, under certain conditions, ejects hot gas along the laser axis to distances several times the kernel size. Whether this ejection occurs, and its intensity and direction, depend on the breakdown parameters and can affect subsequent flame growth in combustible mixtures. One approach to alter, and potentially control, the character of this ejection is a dual-pulse configuration. Detailed simulations are used to study the post-breakdown hydrodynamics in an inert gas, which reproduce key experimental observations. In the first configuration analyzed, a weak pulse disrupts vorticity generation by a stronger pulse, suppressing the ejection that would have been produced by the stronger one alone. In a second configuration, we show that adjusting temporal and spatial separation can access a broader range of phenomenologies in which the ejections can be suppressed, enhanced, or even reversed.