A beam separator of a close packed prism array for low energy electron microscopy

The electron optical properties of a beam separator made of a “Chicane” type close packed prism array proposed by Kolarik et al. [Optik 87 (1991) 1] have been analyzed. The total deflection angle of the illumination beam is 90° and that of the image forming beam is 0°. The second order aberrations are estimated using the eikonal method developed by Rose [Optik 51 (1978) 15] under the SCOFF approximation. It has a limitation in the analysis of the close packed prism array, because of the overlapped fringing field distributions. The magnetic field distributions of the separator are numerically calculated using the three dimensional finite difference method followed by direct ray tracing. The angles of the edge were readjusted by trial and error to get the stigmatic focus of the beam.