| 摘要 |
PURPOSE:To reduce the aberration caused by the deflection, by selecting the parameter of a focusing deflecting device and forming a focusing magnetic field and a deflecting field having nearly the even intensity at the center part of an electromagnetic lens. CONSTITUTION:As shown in the diagram, an electromagnetic lens 1 includes a focusing coil 2, a ring-shaped magnetic matter 3 provided inside the coil 2, an electromagnetic deflector 4, the ring-shape earthed electrodes 5 provided at the front and back sides of the deflector 4, a nonmagnetic spacer 6 that holds the matter 3 and the electrode 5, and an insulator 7 that holds the deflector 4. In such constitution, the position of attachment, the inner and outer diameters, the sectional form, etc. are properly set for the magnetic matter 3. As a result, nearly the even intensity is secured in a proper section at the center part of the lens 1 for the intensity of the focusing magnetic field. In addition, nearly the even intensity is obtained for the deflecting field in a proper section at the center part of the lens 1 by setting properly the position of attachment, the inner and outer diameters, the width, the sectional form, etc. for the electrode of the deflector 4 and the electrode 5 respectively. |
