Nonlinear branched flow of intense laser light in randomly uneven media

Branched flow is an interesting phenomenon that can occur in diverse systems. It is usually linear in the sense that the flow does not alter the properties of the medium. Branched flow of light on thin films has recently been discovered. It is therefore of interest to know whether nonlinear light branching can also occur. Here, using particle-in-cell simulations, we find that in the case of an intense laser propagating through a randomly uneven medium, cascading local photoionization by the incident laser, together with the response of freed electrons in the strong laser fields, triggers space–time-dependent optical unevenness. The resulting branching pattern depends dramatically on the laser intensity. That is, the branching here is distinct from the existing linear ones. The observed branching properties agree well with theoretical analyses based on the Helmholtz equation. Nonlinear branched propagation of intense lasers potentially opens up a new area for laser–matter interaction and may be relevant to other branching phenomena of a nonlinear nature.