  A novel setup allows the Weibel instability and its interplay with the
Biermann battery to be probed in laser-driven collisionless plasmas. Ab initio
particle-in-cell (PIC) simulations of the interaction of short ($ \le ps$)
intense $(a_0 \ge 1)$ laser-pulses with overdense plasma targets show
observable Weibel generated magnetic fields. This field strength surpasses that
of the Biermann battery, usually dominant in experiments, as long as the
gradient scale length is much larger than the local electron inertial length;
this is achievable by carefully setting the appropriate gradients in the front
of the target e.g. by tuning the delay between the main laser pulse and the
pre-pulse.
