FOCUSING OF MIXED-DIPOLE WAVES

A converging mixed-dipole wave is defined as the sum of a converging e lectric-dipole wave and a converging magnetic-dipole wave. In this pap er we study the focusing properties of converging mixed-dipole waves f or the case in which the two dipoles are orthogonal. Within the Debye approximation, we compare both analytical and numerical results for th e converging mixed-dipole wave with those of the converging electric-d ipole wave and also with the results obtained when a linearly polarize d plane wave is focused by a rotationally symmetric, aplanatic system. At large angular apertures, the converging electric-dipole wave is sh own to give best electric-energy concentration and least cross-polariz ation, both in the focal plane and along the optical axis. At angular half-apertures less than 30 degrees, the three types of converging wav es give indistinguishable electric and total energy distributions arou nd the focus. In applications in which one wishes to maximize the elec tric energy density and/or minimize the cross-polarization the converg ing electric-dipole wave is the natural choice as the incident wave.