Addition of energy dispersion characteristics to the diagram of axis intercept for aberration analysis of core-lens

The diagram of axis intercept (Nishi and Takaoka 1]) is extended to consider the energy dispersion characteristic. The operating condition of core-lenses can be optimized by taking into account not only the aperture aberration but also the chromatic aberration. The diagram is applied to a typical core-lens system configured with three point charges of different polarities and is plotted as a function of the electron energy in addition to the starting angle. Near the stigmatic condition, the diagram fits the quadratic dependence on both the energy dispersion and the beam tilt angle. Then, the coefficients of aperture aberration, energy dispersion and chromatic aberration are obtained.