Figure 1. Schematic showing key features of the petawatt laser-solid interaction.

A high-power laser with strength parameter a₀>1 is shown striking an overdense target, interacting over the Lorentz-transformed collisionless skin depth (dark green region), and exciting a highly relativistic electron flux (red spheres) and moderately relativistic ion flux (blue spheres). Laser and excited particle properties are connected across by applying relativistic Rankine-Hugoniot-like relations at the laser-matter interface, allowing abstraction of downstream effects, for example, scattering in the target (light green region). Depiction uses a frame of reference co-moving with the interface.