What is "electron optics"

n. the branch of electronics that deals with beams of electrons and their focusing and deflection by magnetic fields

Electron optics is a mathematical framework for the calculation of particle paths along given electrostatic or magnetostatic fields. The term optics is used because a charged particle beam can be manipulated using magnetic lenses in a similar fashion to the manipulation of a light beam with optical lenses.

Electron optics calculations are, besides other uses, needed for electron microscopes and are also crucial for the design of modern particle accelerators. In paraxial approximation, the calculations can be done using ray transfer matrix analysis.