Fig. 2

PIC simulation results for the interaction of the linearly polarized laser field. The laser intensity is the same as that in Fig. 1. a shows the time evolution of positions of the critical density n_e = (1 ± 0.1)n_c (black dots) and relativistic critical density n_e = (γ ± 0.1)n_c (blue crosses), where \(\gamma = \left( {1 + (1 + R)\epsilon ^2\hat{a}_0^2/2} \right)^{1/2}\) is the relativistic factor of electrons and ε² = 1 for linearly polarized lasers. In obtaining γ, the reflectivity R at the transition time from the hole boring (HB) to the blowout is used. b Time evolution of the reflectivity. The shaded areas in a, b correspond to the transition interval from the HB to the blowout. In c, the electron energy distributions at t = 0.4 and 1 ps are shown by black thin and bold lines, respectively. The slopes of the one-dimensional relativistic Maxwellian energy distribution function >0.5 MeV are shown by the blue-dashed and green-dotted lines assuming the ponderomotive temperature at the maximum reflectivity R = 1, that is T_p = 0.63 MeV, and the Beg scaling T_B = 0.44 MeV, respectively. d, e are the electron phase plots in the longitudinal x direction at times t = 0.4 and 1 ps, respectively