Comparison Between the Properties of Three New Designs of Pinhole Magnetic Lens

Abstract

Three different new designs of an objective pinhole lens were compared. Their magnetic and optical properties were studied using Finite Element Method for Calculating Magnetic Field Distribution (FEM-CMFD) and Magnetic Electron Lens Optical Properties (MELOP) software. The focal length (fo), spherical aberration (Cs), chromatic aberration (Cc), and the resolving power (δ) of each lens were compared at a range of relatively corrected acceleration voltages (Vr = 100 V-100 kV) and a constant excitation of (NI = 5280 A-t (where A represents Ampere and t represents turn)) and current density (2 A/mm2) to find the best design. The L1 lens is similar to the Gemini lens. L2 and L3 are the traditional pinhole lens shape. The L1 lens gave the best results in terms of optical and magnetic properties as its optical properties at medium and low acceleration voltages. L2 and L3 Lenses had almost identical magnetic properties, but the difference was apparent in optical properties.