Theory of electron-optical achromats and apochromats

A detailed theoretical formulation of the primary and secondary chromatic aberrations of electron-optical systems with a straight optic axis is outlined. To simplify the mathematical expenditure only systems composed of magnetic round lenses and magnetic and electrostatic quadrupoles are taken into account. By appropriately arranging these elements, it is possible to construct feasible electron-optical analogues of light-optical achromats and apochromats.