| 摘要 |
<p>An aberration correction system is offered which is for use in an electronmicroscope and which produces a negative spherical aberration and corrects a higher-order aberration. The aberration correction system has threestagesof multipole elements (21, 22, 23) which respectively produce fields of 3-fold symmetry with respect to the optical axis (11). The middle stage of multipole element (22) produces the field of the 3-fold symmetry within a plane perpendicular to the optical axis (11). The rear stage of multipole element (23) also produces the field of the 3-fold symmetry within the plane perpendicular to the optical axis (11). Any two stages of multipole elements are disposed in directions not to cancel out the 3-fold fields. However, the three stages of multipole elements are so disposed as to cancel out 3-fold astigmatisms.</p> |
