ADDITION OF DIFFERENT CONTRIBUTIONS TO THE CHARGED-PARTICLE PROBE SIZE

Addition of different contributions to the charged particle probe size . The diameter containing a Fraction of the current is used as the mea sure of the charged particle probe size. This has, particularly in the case of analytical microscopies, proven to be a more practical measur e than those based on widths of the current density distribution. The diameter of current carrying beams of finite brightness and energy spr ead is enlarged by spherical and chromatic aberrations of the lens sys tem and (for electron probes) by diffraction. The only correct way to add these contributions to find the total probe size is by elaborate e xact ray-tracing or wave optical simulations. Mie have constructed a s imple root-power-sum algorithm, in terms of analytical functions, for the approximate addition of the various individual contributions. The total probe diameter yielded is quire close to that given by exact cal culations.