3D PIC/MCC simulation of laser-guided streamer discharges in atmospheric air

Powerful lasers hold promise for guiding streamer discharges in air, with applications ranging from plasma etching to lightning control. This paper numerically investigates the guidance of positive streamers by laser-produced pre-ionization (a uniform ionization trail consisting of free electron-ion pairs) in air with a 3D PIC/MCC model. Initially, the streamer grows toward the laser beam due to the electrostatic attraction caused by charge separation within the laser channel. As laser-produced electrons drift near the streamer, they trigger electron avalanches, forming a distinct "laser-produced streamer branch". This branch then propagates along the laser path, influenced by both electrostatic repulsion from the laser's positive ions and the guiding effect of the laser's electrons. By decoupling the impact of laser-produced pre-ionization on the electric field and free electron distribution, our simulations reveal that free electrons are the dominant factor for guiding. However, the electrostatic effect is enhanced at higher laser densities and can also guide the streamer individually. The formation of laser-guided streamers is primarily determined by whether laser-produced electrons can form a self-sustaining streamer branch. This process is highly dependent on the initial laser intensity and the electric field where the laser electrons connect with the streamer. Additionally, when the laser beam is positioned closer to the streamer, the effectiveness of laser guiding is significantly enhanced, and the number of streamer branches is greatly reduced. The angle of the laser beam also affects guiding due to variations in the electric field at the laser-streamer connection point.