4π Focusing with single paraboloid mirror

Creating small bright or dark focal spots with good spherical symmetry requires 4π focusing, usually achieved by using two counter-propagating beams and two high NA lenses that need to be positioned with interferometric accuracy. We investigate a simple alternative way of focusing light to a small and uniform bright or dark focal spot. It only requires a single parabolic mirror illuminated with a single beam from one direction, resulting in a robust and compact setup. The focal spot distribution is tailored by optimizing the polarization, intensity and helicity of the incoming illumination.