公开(公告)号：CA1140197A

公开(公告)日：1983-01-25

申请号：CA365137

申请日：1980-11-20

Applicant: CONTROL DATA CORP

Inventor： BONO DAVID C ,  FISHBEIN MARVIN ,  HARTE KENNETH J

IPC: H01J3/18 ,  H01J37/12 ,  H01J37/305 ,  H01J37/317 ,  H01J29/62

Abstract: A unipotential electrostatic lens and method of operation for charged particle beam tubes of the electron beam, compound fly's eye type having both coarse and fine deflection sections wherein the objective lens assembly may lack coaxial symmetry about the lens axis. The unipotential lens comprises an assembly of axially aligned electrostatic lens elements with each lens element having an array of micro lenslet apertures and with each set of axially aligned micro lenslet apertures forming a micro lenslet. Preferably, there are three such lens elements in the assembly with a high voltage excitation potential supplied to the center lens element. A dynamic focus correction potential derived from the deflection potentials applied to the tube is supplied to the entrance outer lens element closest to the electron gun of the beam tube. The remaining outer lens element is maintained at system ground reference potential. In preferred arrangements, a fixed offset potential is added to the high voltage excitation potential supplied to the center lens element and a compensating offset potential is supplied to the entrance outer lens element along with the dynamic focusing correction potential to thereby distribute and minimize the effect of deflection sweep and astigmatism errors which otherwise might be introduced by the uncompensated dynamic focus correction potential.