Fig. 1. Monte Carlo ensemble for 103 trajectories: (a) from ionization at an intensity of 1.3×1017  W/cm2 and its return to the core 70 a.u. later. Symbol is plotted for every 1.1 a.u. time step from ionization at t=0. Color mapping used for propagation time after ionization. The XZ- and XY-plane projections show the rapid spreading of the electron from ionization at the origin. In addition, the increasing distance between the 1.1 a.u. time steps in the plane projections indicate the electron acceleration in the field and the tilt of the electron wave front from the Lorentz force (XZ-projection); (b) coordinate system for the elastic scattering from the nucleus shown in (a); (c) scattering potentials for Ne+, Ne8+, Ar8+, and Xe8+. Atomic units (a.u.) are used.

Fig. 2. Angle-integrated photoelectron energy distributions for Ne+ (black, Up=2.6  a.u.), Xe8+ (blue, Up=38  a.u.), Ar8+ (green, Up=115  a.u.), and Ne8+ (red, Up=770  a.u.) as a function of the final photoelectron energy. Yield is given in electrons per unit Up energy. For each species, we show the nonrelativistic dipole (thick, dash) and the relativistic full field (solid) yields. Energy integration regions for the angular distributions shown in Fig. 3 are highlighted.

Fig. 3. Photoelectron angular distributions calculated for B=0, for Ne+ (solid, black), Xe8+ (dotted, blue), Ar8+ (dash, green), and Ne8+ (thick solid, red): (a)–(c) nonrelativistically; (d)–(f) full field, relativistically; (a), (d) for energies Up±0.5Up; (b), (e) for energies 3Up±Up; and (c), (f) for energies 7Up±Up. Yields are normalized to the peak value at that energy (Fig. 2).