Patent ID: 7839979

Claim:
An electron optical apparatus comprising components arranged along an optical axis: a cathode including an emitter, wherein the emitter has a substantially planar surface for homogeneously emitting electrons in an electron beam from the substantially planar surface with a reduced lateral energy component of the emitted electrons transverse to the optical axis; an anode for accelerating the emitted electrons in a direction essentially along the optical axis; a first magnetic quadrupole lens for deflecting the accelerated electrons to focus the electron beam and having a first yoke, the first magnetic quadrupole lens further having a magnetic quadrupole gradient for focusing the electron beam in a first direction and defocusing the electron beam in a second direction perpendicular to the first direction; a second magnetic quadrupole lens for further deflecting the accelerated electrons to focus the electron beam and having a second yoke, the second magnetic quadrupole lens further having a magnetic quadrupole gradient for focusing the electron beam in the second direction and defocusing the electron beam in the first direction, wherein the magnetic quadrupole gradient of the first and second magnetic quadrupole lenses are rotated about 90 degrees with respect to each other, further wherein a sequential combination of the first and second magnetic quadrupole lenses provides a net focusing effect in both first and second directions of a focal spot of the electron beam; and a homogeneous magnetic dipole lens for further deflecting the accelerated electrons of the electron beam in order to shift the focal spot of the electron beam in a plane perpendicular to the optical axis on a target.