A useful potential solution V(x,y,z) for symmetric rectangular stepwise constant-potential boundaries at y = ±Y

Three-dimensional Laplace-equation problems are generally quite difficult. In a number of electron-optics devices, a rectangular structure of stepwise constant potentials Vmnat y = ±Y form symmetric boundaries. It is shown that useful solutions of the potential V(x, y, z) in the interior of such devices can be developed systematically.