Effect of the Outer Pole Length on the Optical Properties in Gemini Lens

Abstract

In order to get some of the most important optical and geometrical properties of scanning electron microscope lens, Such as focal length, lens aberration (spherical and chromatic aberration), Axial magnetic field distribution, trajectory of the electron beam, diameter of the electron probe in this work. A computer programs used to achieve the results in objective lens which called Gemini lens.by changing the outer pole length of lens to get a better optical property. The results under constant lens excitation (NI=1000 A-t) and accelerating voltage (Vr=8 KV) are (f=3.93mm, Cs=2.59mm, Cc=2.87mm) and the magnetic field distribution Bz =1.72 tesla