The femtosecond laser filamentation has attracted extensive attention due to its potential applications in many fields.Recently, it has been reported that multi-filamentation can be suppressed at high laser power either by using a phase plate or lens tilting , resulting in single filamentation at higher peak intensities. 

Researchers at State Key Laboratory of High Field Laser Physics——Shanghai Institute of Optics and Fines Mechanics (SIOM/China) have observed a new phenomenon, namely, formation of stable branched filaments, when astigmatically focusing the intense femtosecond laser pulses in air using a pair of orthogonal cylindrical lenses.[ Applied Physics B: Lasers and Optics . 103: 435–439(2011)]

They observe filament branching with astigmatically focused femtosecond laser pulses. This filament branching is successfully reproduced by numerical simulation.The results suggest that the interference of the background energy and the energy diffracted from the filament are responsible for the filament branching. Their work extends the concept of control of the femtosecond laser filamentation with astigmatically focused pulses, which has been previously used for shortening the filament length. In addition, the capability of splitting an intense pulse into two by controllable branching angle may allow one to simultaneously send intense laser pulses to two remote locations.