Patent Number: 061040347
Section: claims

1. An objective lens construction for influencing an electron beam comprising: a single-pole magnetic lens;  an electrostatic lens having a first electrode and a second electrode coaxial with said first electrode;  means for connecting said electrodes to a different electrical potentials; and  one of said electrodes being at least partially accommodated in said magnetic lens and the other of said electrodes extending beyond said magnetic lens in the direction of said electron beam and being wholly external of said magnetic lens. 2. The construction according to claim 1 wherein each of said electrodes is tubular. 3. The construction according to claim 2 wherein one of said electrodes telescopes with the other of said electrodes. 4. The construction according to claim 1 wherein said electrodes are of corresponding cross sectional configuration and area. 5. The construction according to claim 1 wherein said objective lens has an optical axis about which the magnetic lens and said electrodes are symmetrical, said electrodes being displaceable relative to one another in the direction of said optical axis. 6. The construction according to claim 1 wherein said other of said electrodes is apertured at that end thereof remote from said magnetic lens. 7. The construction according to claim 1 wherein one of said electrodes is slotted axially and forms multipole elements. 8. The construction according to claim 7 wherein said slotted electrode constitutes an electrostatic deflector. 9. The construction according to claim 7 wherein said slotted electrode constitutes a stigmator. 10. The construction according to claim 7 including magnetic multipoles superimposed on electric multipole elements. 11. The construction according to claim 10 wherein said electric multipoles and said magnetic multipoles are of such number and are so arranged as to form crossed electric/magnetic dipole transverse fields. 12. The construction according to claim 10 wherein said electric multipoles and said magnetic multipoles are of such number and are so arranged as to form crossed electric/magnetic quadropole transverse fields. 13. The construction according to claim 1 wherein said electrostatic lens is operable to retard the particle beam.