Compound electron lens for electron microscope and the like

Claim 2

A compound electron lens comprising: at least two annularly wound exciting coils disposed coaxially; magnetic cover means surrounding said exciting coils to form a closed magnetic circuit common to said exciting coils; at least one magnetic pole portion formed in the annular hollow of each of the coils; magnetic path means disposed between the two exciting coils to form a magnetic path extending from said magnetic pole portion to said cover means; air gap means positioned in said magnetic path means for bypassing flux generated by the coils and flowing through the closed magnetic circuit; means for supplying exciting current to the individual coils; and means for switching the polarity of the exciting current supplied to one of the coils with respect to the other coil so that spherical aberration is minimized over a wide range of magnifications.

Claim 3

A compound electron lens as defined in claim 1, further including at least one alignment adjusting screw extending through said magnetic cover means for finely adjusting the length of the gap in said magnetic path means.

Claim 4

A compound electron lens as defined in claim 1, further including another annularly wound exciting coil disposed between said two coils and an additional magnetic pole portion formed in the annular hollow of the additional coil.

Claim 5

A compound electron lens as defined in claim 1, in which said exciting current supplying means comprises one adjustable power source, and said exciting current polarity switching means comprises one switch, said power source being connected to each of the coils through said switch, whereby the polarity of the exciting current supplied to one of the coils with respect to the other coil can be switched by means of said switch.

Claim 6

A compound electron lens comprising: at least two annularly wound exciting coils disposed coaxially, a magnetic cover surrounding said exciting coils in common and having first and second lens gaps therein formed in the portion extending within the annular hollow of the coils adjacent the respective coils, an inner magnetic path member extending as a partition within the cover between said coils, said inner magnetic path member being spaced from said cover at one end thereof so as to leave a gap for bypassing the flux from the coils, means for supplying exciting current to the individual coils, and means for switching the polarity of the exciting current supplied to one of said coils so that spherical aberration is minimized over a wide range of magnifications.

Claim 7

A compound electron lens comprising: at least two annularly wound exciting coils disposed coaxially, a magnetic cover surrounding said exciting coils in common and having first and second lens gaps therein formed in the portion extending within the annular hollow of the coils adjacent the respective coils, an inner magnetic path member extending as a partition within the cover between said coils, said inner magnetic path member being spaced from said cover at one end thereof so as to leave a gap for bypassing the flux from the coils, means for supplying exciting current to the individual coils, and means for switching the polarity of the exciting current supplied to one of said coils so that spherical aberration is minimized over a wide range of magnifications.

Claim 8

A compound electron lens as defined in claim 5, wherein said inner magnetic path member is split into two adjacent portions connected respectively to the inner magnetic cover portions forming part of the first and second lens gaps, and further includIng at least one alignment adjusting screw extending through said magnetic cover for adjusting the position of at least one of the adjacent portions of said inner magnetic path member.

Claim 9

A compound electron lens as defined in claim 5, wherein the gap formed by said inner magnetic path member is disposed inside the inner magnetic cover portion forming part of said first and second lens gaps.

Claim 10

A compound electron lens as defined in claim 5, further including another annularly wound exciting coil disposed between said two coils and having a cavity with a magnetic pole portion formed in the annular hollow of the additional coil.

Claim 11

A compound electron lens comprising: first, second and third annularly wound exciting coils disposed coaxially; magnetic cover means surrounding said exciting coils to form a closed magnetic circuit common to said exciting coils; at least one magnetic pole portion formed in the annular hollow of each of the coils; first and second magnetic path means disposed between the first and second exciting coils and the second and third exciting coils, respectively; air gap means positioned in said magnetic path means for bypassing flux generated by the coils and flowing through the closed magnetic circuit; means for supplying exciting current to the individual coils; and means for switching the polarity of the exciting current supplied to one of the coils with respect to the other coil so that spherical aberration is minimized over a wide range of magnifications.

Claim 12

A compound electron lens comprising: first, second and third annularly wound exciting coils disposed coaxially; magnetic cover means surrounding said exciting coils to form a closed magnetic circuit common to said exciting coils; at least one magnetic pole portion formed in the annular hollow of each of the coils; first and second magnetic path means disposed between the first and second exciting coils and the second and third exciting coils, respectively; air gap means positioned in said magnetic path means for bypassing flux generated by the coils and flowing through the closed magnetic circuit; means for supplying exciting current to the individual coils; and means for switching the polarity of the exciting current supplied to one of the coils with respect to the other coil so that spherical aberration is minimized over a wide range of magnifications.