Figure 5

Two sets of simulation results for evolution of the Coulomb field. The first simulation (a,b) includes a full laser plasma interaction while the second one (c–e) models a simplified case where an electron bunch is propagating in vacuum. The “0” positions in the x direction of the figures are the plasma-vacuum boundary. (a) and (b) correspond to simulation times of 7.21 ps and 7.74 ps that are counted from the beginning of the laser interaction with plasma. The laser pulse is denoted by orange colour. The E _y component of low frequency electric fields are illustrated by blue and red colours corresponding to different field directions. The green area is the plasma bulk and electrons outside the plasma region are shown as black dots. (c) and (d) show the E _y field structures at times of 8.01 ps and 8.84 ps that are counted from the emergence of the electron bunch at the left boundary of the simulation box. The spherical red dashed curves in (c) and (d) denote an imagined light front expanding at the speed of c. A zoomed picture of the purple dashed rectangular area in (d) is shown in (e). In a small area, the angle of incidence and angle of refraction of the Coulomb field are denoted as θ _s and θ _sc , respectively. The red dashed lines in (e) represent a signal wavefront in the field.