| 摘要 |
The invention relates to a corrector with a straight optical axis for eliminating color and aperture aberrations in optical particle lenses. Said corrector is equipped with multipole elements in the form of electric and/or magnetic quadrupole and octupole elements. According to the invention, at least twelve quadrupole elements and ten octupole elements should be provided, wherein three quadrupole elements and two octupole elements of said elements are assembled into a group. The groups are arranged successively along the optical axis, wherein a first symmetrical plane is defined between the first and the second group, a second symmetrical plane is defined between the second and third group and a third symmetrical plane is defined between the third and fourth group. The multipole elements from one group to another correspond to each other in pairs, wherein the multipole elements of the corresponding following group are positioned in reverse order along the optical axis in comparison with the corresponding multipole elements of the preceding group. The structure and refractive powers of the multipole elements that correspond to each other are mirror-symmetrically configured relative to the corresponding symmetrical plane between the groups. At least two of the above-mentioned quadrupole elements generate electric-magnetic quadrupole fields, wherein said quadrupole elements are preferably arranged in a mirror-symmetrical manner relative to the second or to all symmetrical planes. In addition to the above-mentioned octupole elements, another such element is arranged in the first and third symmetrical planes. The corrector enables the transmission of extremely large image fields while the optical quality remains the same due to the fact that image aberrations outside the axis can be corrected.
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