| 摘要 |
This invention concerns a lens system, particularly for focusing electrons, with a cylindrical lens with pole shoes or electrodes, between which an aperture is located. This aperture has a slot-shaped cross section perpendicular to the optical axis of the lens. The cylindrical lens (4) is combined with a magnetic lens (1) with which a quadripole field can be produced. The lenses are arranged with little or no distance between them and their optical axes run parallel to one another. The quadripole lens (1) has a slot-shaped aperture (10) which is oriented parallel to the opening (9-11) of the cylindrical lens (4). The focusing plane of the quadripole lens (1), which comprises the optical axis (19), is oriented parallel to the longitudinal axes of the apertures (9-11) and its defocusing plane perpendicular to the longitudinal axes. The refractive power of the cylindrical lens (4) can be set at twice that of the quadripole lens (1).
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