Collimated proton beams from laser interaction with a slab having a hole on its backside are investigated using particle-in-cell simulation. The hot target electrons driven by the laser expand rapidly into the hole. However, at the hole's corners the electrons are strongly compressed and an intense electron jet is emitted from each corner, tightly followed by the ions. The plasma jets focus and collimate along the axis of the hole and can propagate without divergence within the hole. The effect of the hole diameter on the collimated proton beam is considered.
