Figure 5

(a,b) are the space of the accelerated electrons at different laser propagation distances in nitrogen, corresponding to z = 3500 μm and 5500 μm. (c and d) show snapshots of the longitudinal wakefield potential (red line) and strength (blue line) at the time when the test electron is born and injected, where the black dashed lines in the two plots mark the electron birth and injection positions, respectively.