Figure 1

Schematic of a 4Pi system constructed by two confocal high-NA objective lenses. A sectional-uniform line source antenna, along which the current is constant, is centered at the foci of two high-NA objectives and aligned along the optical axis (denoted by yellow arrows). The field radiated from the antenna (denoted by black arrows) is completely gathered by two identical objective lenses to their pupil planes. Next, the field at the pupil planes is inversely propagated (denoted by red arrows) with a relative π phase shift (denoted by blue arrows) and focused by the 4Pi focusing system.