公开(公告)号：US3629578A

公开(公告)日：1971-12-21

申请号：US3629578D

申请日：1969-01-27

Applicant: PHILIPS CORP

Inventor： POOLE JAN B LE

IPC: H01J29/76 ,  H01J37/14 ,  H01J37/147 ,  H01J37/153 ,  H01J37/252 ,  H01J37/29 ,  H01J37/26 ,  G01N23/22

CPC classification number: H01J37/147 ,  H01J29/76 ,  H01J37/14 ,  H01J37/153 ,  H01J37/252 ,  H01J37/29

Abstract: A magnetic deflecting system for deflecting a beam of charged particles comprising a pair of mirror symmetrical pole-pieces on opposite sides of a plane of symmetry passing through a principal ray of the beam. The surfaces of the pole-pieces have contours which define a space between the pole-pieces which varies stepwise in the direction of the main ray with a centrally constricted portion which defines a region of highest field strength. The deflection system has a field strength at which the main ray entering the deflection system, which ray extends at least partly in the direction of the constricted space between the pole-pieces, follows a curve which passes in front of the pole-pieces in the region of the highest magnetic field strength. Means are provided to produce a field strength distribution at the area of the minimum distance of the curve from the region of the highest field strength which, measured in the direction towards the highest field strength, exhibits at that area a locally stronger field strength gradient. This field strength distribution affects the beam so that a curvature of image lines transverse to the plane of symmetry in a plane transverse to the main ray is counteracted, i.e., electron-optical aberrations are reduced.