Creation of a sub-diffraction limit 3D focal spot array

We report a method of the construction of a sub-diffraction limit 3D focal spot array by a 4Pi focusing system consisting of two high-numerical-aperture (NA) objectives. The approach can be achieved by using inverse focusing of the field radiated from a spaced dipole array mounted along the optical axis at the focal points of two high-NA lenses. The illumination required to produce a 3D spot array in the pupil plane is a radially polarized beam with spatial amplitude modulation based on the reverse thinking, and the resulting 3D focal spot array has uniform intensity, controllable number, adjustable position, and adjustable spacing.