DE1022329B - Arrangement for the coarse change of the focal length of a magnetic pole piece lens for corpuscular beam apparatus - Google Patents

Description

GERMAN

With magnetic pole piece lenses for corpuscular beam devices, For example, for electron microscopes, it is known to have a coarse regulation of the Perform lens focal length in that the entire pole shoe system, so both pole shoes of the Lens, are movable transversely to the beam axis. For example, a plurality of are arranged on a turntable such pole shoe systems with different pole shoe bores and Polschuhabständeii, so that you can switch on a different lens focal length by turning this holder during operation. Systems of this type are used and are used in electron microscopes, in particular in projectives here to change the final image enlargement in several rough steps. You have to be with such Control devices for the lens focal length accept that for the arrangement of such Turntable a relatively large axial length of the device is claimed because in the Turntable both pole pieces must be accommodated.

The invention relates to an arrangement for changing the focal length of a magnetic in coarse steps Pole shoe lens for corpuscular beam apparatus with a pole shoe holder that can be adjusted transversely to the beam axis. According to the invention, a fixed pole piece of the lens is a through Rotating or rectilinear shifting adjustable holder with several pole pieces associated with the have different holes and / or distances from the fixed pole piece and by the holder movement one after the other can be compared to the immovable pole piece.

The arrangement for the coarse regulation of the focal length can compared to the known devices discussed above with a smaller axial length of the movable pole shoe haker and accordingly also with less effort au associated drive means and lighter weight of the entire adjustable mechanism. the The fact that the fixed pole piece of the lens is effective in every operating position is a nuisance the desired control option not. You will choose this Palschuh in its dimensions so, that he has good imaging conditions for all settings of the mobile pole shoe haker working with it Has. Depending on the task at hand, you can choose the shape and bore of this Adapt the fixed pole piece to the setting level of the movable pole piece, which are of particular importance in the case in question. So, for example, you can use the fixed Preferably adapt the pole piece of the operating level that has the shortest focal length and arrangement

for changing the focal length of a magnetic pole piece lens in steps

for corpuscular beam devices

Applicant:
Siemens & Halske Aktiengesellschaft,

Berlin and Munich,
Munich 2, Witteisbacherplatz 2

Manfred Eisfeldt, Berlin-Tempelhof,

and Dipl.-Ing. Gerhard Simon, Berlin-Siemensstadt,

have been named as inventors

is accordingly assigned to the highest magnification.

The arrangement can be used with magnetic lenses of any kind, i.e. both with lenses with electromagnetic excitation work as well as permanently magnetically excited lenses. In both cases One becomes, for example, with one consisting of an outer and an inner cylinder and two cover parts Magnetic circuit work in which a lens gap between the inner cylinder and the one cover part is provided, and that, for. B. the adjustable, multiple pole pieces containing the one pole piece holder Cover part of the magnetic circuit is assigned. In this case one has the particular advantage that a perfect symmetrical structure in the parts of the lens is possible, each in the operating position lead magnetic flux. But it is also possible to attach such an adjustable pole piece holder to the inner cylinder of the magnetic circuit. The field diaphragms required for the new arrangement will be assigned to the pole pieces that are attached to the adjustable pole piece holder. To this In every operating position of the coarsely adjustable lens you always have the right one Field diaphragm switched on in the beam path. In the drawings there are schematically a number of Illustrated embodiments of the invention. Fig. 1 shows a longitudinal section through a double lens system, there·? as imaging optics of a two-stage electron microscope can be applied. With 1 the objective, with 2 the projective of the lens arrangement designated. To excite the lens, a preferred

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wise from several permanent magnets 3 existing System that has the inner cylinder 4 with the upper pole and a cover 5 with the lower pole of the magnetic circuit. 6 with an upper cover, with 7 the outer surface of the lens system * is designated. These parts are made of magnetic material. As a spacer between the covers 5 and 6 and the inner cylinder 4 are brass rings 8 and 9. The two belong to the pole shoe system of the lens Pole pieces 10 and 11. The upper pole piece 12 of the projection lens is connected to the inner cylinder 4 of the magnetic circuit firmly assembled.

A straight pole piece holder that can be adjusted transversely to the beam axis is used to regulate the projection lens provided, which in the position shown has a pole piece 14 with a relatively narrow bore the stationary pole piece 12 opposite. The holder 13 can be adjusted with the aid of an external adjustment rod

15 in two more, preferably palpable by locking Settings are shifted so that the pole piece 16 or the pole piece 17 then becomes effective. As the figure reveals, the pole pieces 14 are.

16 and 17 designed with different bores and different axial spacing from the pole piece 12, so that depending on which of the pole pieces is switched on. there is a change in the focal length in three rough steps.

A second expedient embodiment is shown schematically in FIG. In this case the Magnetic circuit from the outer cylinder 21, the inner cylinder 22 and the two cover parts 23 and 24, respectively composed. With 25 permanent magnets are designated, which are used to excite the system. the non-magnetic rings 26 and 27 ensure the spacing between the cover parts 23 and 24 and the inner cylinder 22. The pole shoe system of the lens is denoted by 28; 29 is the in this case lower pole piece of the projection lens assembled directly with the inner cylinder 22. With this immovable pole piece, a turntable 30 works together, in which preferably four pole piece systems different diameter of the pole shoe hole and different distance from the fixed Pole shoes are arranged. With 31 and 32 two such different pole pieces are designated. Of the Turntable 30 can around the axis of rotation 33 with the aid of a drive not shown in the figure during the operation of the microscope can be adjusted, so that optionally one of the preferably four different Pole shoe settings take effect. In this embodiment, a plate is designated by 34, which carries the turntable and which is firmly connected to the cover 24. In the arrangements shown in Fig. 1 and 2 has the advantage that in the the magnetic flux leading part of the lens a completely symmetrical structure of the arrangement possible is.

While in the two previously discussed Ausfülirungsbeispielen the adjustable pole shoe holder is assigned to the lower plate of the magnet system, Fig. 3 shows another useful embodiment with a pole piece turntable, which the inner cylinder of the magnet system is assigned. 41 is the outer cylinder, 42 is the inner cylinder of the Magnetic circuit designated. 43 and 44 are the associated cover pieces. As non-magnetic spacers The brass rings 45 and the brass sleeve 46 are used here. The permanent magnets are used to excite the magnet system 47. which are radially magnetized as indicated. The lens pole shoe system is denoted by 48. In this case the fixed pole piece 49 of the projection lens is in the cover piece 44 provided. A turntable 50 is used to adjust the focal length of the projector Axis 51 with the aid of an * outer, not shown Shoot can be rotated. This turntable 50 can contain, for example, four different pole pieces,

ίο each in the operating position the lower end 52 of the inner cylinder 42 touch. In the position shown a pole piece 53 is switched on, which has a relatively narrow bore. so that in this case a very short focal length lens is switched on. With 54 the opposite pole piece is referred to, the has a correspondingly larger bore and offers the possibility of a correspondingly longer lens focal length to adjust. The respective required field stops 55, 56 are attached to the pole pieces assign, which are attached to the adjustable pole piece holder, so that one then inevitably for each In the operational position, the necessary associated field diaphragm is also switched into the beam path Has.

Hei the illustrated embodiment, the focus of the image can be done in that the Operating voltage of the cathode of the beam generator is continuously variable. But Alan can too Think of an axial mechanical adjustment of the specimen cartridge 57.

Claims (4)

PATENT CLAIMS: 1. Arrangement for the rough change of the focal length of a magnetic pole piece lens for Corpuscular beam apparatus with a pole shoe holder that can be adjusted transversely to the beam lens, in particular for permanent magnetic lenses, characterized in that a fixed The pole piece of the lens has a holder that can be adjusted by rotating or shifting in a straight line is assigned several pole pieces, the different holes and / or distances from have fixed pole piece and the immovable one after the other due to the holder movement ⁴ S pole piece can be juxtaposed. 2. Arrangement according to claim 1 with one of the outer and inner cylinders and two cover parts existing magnetic circuit, in which between the tune cylinder and a cover part - a lens gap is provided, characterized in that an adjustable pole shoe holder the one cover part of the magnetic circuit is assigned. 3. Arrangement according to claim 1 with one of the outer and inner cylinders and two cover parts existing magnetic circuit in which there is a lens gap between the barrel cylinder and a cover part is provided, characterized in that an adjustable pole piece holder is attached to the inner cylinder assigned. 4. Arrangement according to claim 1 or one of the following, characterized in that each necessary field diaphragms are assigned to the pole pieces, the shoe holder in the adjustable pole are attached. Considered publications:
German patents Xr. 891 006, 914 532, 616. 1 sheet of drawings © 70 »848-269 12. 57