Polarization smoothing in a convergent beam

A birefringent wedge in a collimated 351-nm beam provides polarization smoothing at the Omega laser facility and provided it for the Nova laser. At the National Ignition Facility, the best place to put such an optic is after the final focus lens. In a converging beam, a flat birefringent plate can closely mimic the polarization-smoothing action of a wedge. In this new design the flat plate is nearly a Z-cut crystal; for the wedges, the optical axis of the crystal lies far from the plate normal.