Ponderomotive laser channelling and multi-channelling in homogeneous   underdense plasma
  We have studied laser pulse channeling in underdense plasma by means of analytical theory and 3D PIC simulations. The most significant result of this paper is the demonstration of the single fully evacuated stationary channel solution can be reached an asymptotic state in PIC simulations. In the lower density and for a laser power above channeling power, we were able to reproduce in PIC simulations the analytical curve. We showed that single channels are stable structures against symmetric perturbations. We also studied the formation of the ring structure in theory and simulations. An evacuated ring enclosed by an electron filament was observed in our 3D simulations. However they always coexist with the main laser mode. The threshold power for ring structure formation is found. Our studies on stability of the rings against asymmetric perturbations show that ring structure is not stable against azimuthal perturbations. The growth rate of the instability is shorter for higher densities and it is therefore more effective at higher densities. 
Neda Naseri, Denis Pesme, Wojciech Rozmus
physics.plasm-ph