| 摘要 |
PROBLEM TO BE SOLVED: To provide a Wien filter which enables suppression of secondary astigmation. SOLUTION: The Wien filter has twelve poles. Each pointed head of each pole, which faces a light axis in an XY plane which is perpendicular to the light axis, has a rotational symmetry of twelve rotational steps around the light axis as the center axis. COPYRIGHT: (C)2003,JPO
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