  In simulations of a 12.5PW laser (focused intensity I = 4x10^23W/cm^2)
striking a solid aluminium target 10% of the laser energy is converted to
gamma-rays. A dense electron-positron plasma is generated with a maximum
density of 10^26/m^3; seven orders of magnitude denser than pure e-e+ plasmas
generated with 1PW lasers. When the laser power is increased to 320PW (I =
10^25W/cm^2) 40% of the laser energy is converted to gamma-ray photons and 10%
to electron-positron pairs. In both cases there is strong feedback between the
QED emission processes and the plasma physics; the defining feature of the new
`QED-plasma' regime reached in these interactions.
