CAD in light optics and electron optics

In 1854 J. C. Maxwell devised his fish-eye lens a sphere with a radially diminishing refractive index [*1. The optical characteristics of this lens, which can produce aperfect image of an object, as the computer plot above suggests, are fairly easy to calculate analytically. This is not generally the case with optical elements of varying refractive index as used today for data transmission. The refractive index distribution for light-optical elements can be more or less freely chosen, but for electron-optical elements the Laplace equation or Maxwell's equations have to be taken into ac~ount when determining the corresponding distribution. In the absence of analytical solutions it is necessary to resort to numerical methods of approximation. Light optics and electron optics have developed quite independently, so it is somewhat surprising to find that the same software is now being used at Philips Research Laboratories in Eindhoven for solving problems in both fields. Different designs can thus be optimized in a short time by CAD (Computer-Aided Design). Hypothetical experiments can be performed on the monitor screen in the first stage of development, so that there is no need for the timeconsuming and expensive construction of experimental models.