electron lens

A component that converges or diverges an electron beam by the action of a magnetic field or an electrostatic field.
The magnetic field and the electrostatic field, which are rotationally-symmetric with respect to the optical axis of the electron beam, have an action of a convex lens to converge the electron beam. However the concave lens, which is possible to make in the light optical lens, cannot be created in the electron lens. A lens created by the magnetic field is called the magnetic field lens and a lens created by the electrostatic field is called the electrostatic lens.
The magnetic field lens is generally used for the objective lens of SEM. In the magnetic-electrostatic compound lens recently developed, an electrostatic lens is put under a magnetic lens. The Wehnelt electrode of the electron gun acts as an electrostatic lens to form the crossover of the electron beam.