For a large numerical aperture, the focusing of long-wavelength edge and synchrotron radiation from an electron is modeled. The central obscuration of Schwarzschild optics is also considered. For a numerical aperture of 0.65, typical of an infrared microscope, the maximum energy density of the focused electric field is reduced by similar to 50, compared to paraxial focusing calculations that do not consider a central obscuration. With a large numerical aperture, some light rays strike the focal plane at grazing incidence, producing longitudinally polarized radiation. For a numerical aperture of one, focused edge and synchrotron radiation produce similar spots of longitudinally polarized radiation, whose diameter is about one-half wavelength. The small size and large radiation field of these spots may be useful in experiments that require localized radiation with polarization perpendicular to the sample surface. (C) 2002 Elsevier Science B.V. All rights reserved. References: 19
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