| 摘要 |
PURPOSE:To obtain a high resolution magnetic field lens with a reduced spherical aberration coefficient by placing magnets so that the distance from the side surface of the lower magnet to a circle, the center of which is the lower end of the upper magnet and the radius of which is a distance between said end and the top of the lower magnet, is increased downwardly. CONSTITUTION:A circle the center of which is the lower end (P) of an upper magnet 1 and the radius (r) of which is a distance between said end (P) and the top (Q) of the lower magnet 2 passing at the point (Q) is described, (n) is a junction point of a small angle theta1 side surface and an adjacent large angle theta2 side surface, and lopt is a distance in the optical axis direction from the upper end of the lower magnet 2 to point (m), where the junction is fixed at the position llim so that distance from the side surface of the lower magnet is increasing downwardly. Thus a magnetic flux is focused to the top of the lower magnet effectively, and a high resolution magnetic field lens with extremely reduced spherical aberration coefficient can be obtained. |
