Electrostatic lens, and parallel beam generation device and parallel beam convergence device which use electrostatic lens and collimator

A parallel beam generation apparatus comprising an electrostatic lens and a planar collimator plate, said electrostatic lens comprising:

• an axisymmetric or substantially axisymmetric aspherical mesh, said mesh being concavely shaped with respect to a point source or a focusing spot;
• and
• one or more axisymmetric or substantially axisymmetric electrodes;
• wherein said aspherical mesh has a major axis from a vicinity of a center of a mesh opening to a mesh center position or said aspherical mesh has a spheroid shape in which the vicinity of the mesh opening expands inwardly with a convex curvature;
• wherein a mesh electrode connected to said aspherical mesh has an opening with a radius R1, and a first electrode adjacent to the mesh electrode has an opening with a radius R2, and a ratio of R2 to R1 is in the range of 1.2 to 1.6;
• wherein a ratio of the major axis radius to a minor axis radius in said spheroid is in the range of 1.0 to 2.0;
• said parallel beam generation apparatus further characterized in that:
• said electrostatic lens and said planar collimator plate are positioned coaxially with each other, with an acceptance angle of charged particles generated at a point source being ±60°;
• said planar collimator plate is furnished with pores, each pore having an aspect ratio defined as a ratio of pore diameter to pore length, the aspect ratio of 50% or more of said pores being in a range from 1:5 to 1:20;
• said planar collimator plate functions as a band-pass filter for selecting only charged particles of a specific kinetic energy;
• whereby in operation of the parallel beam generation apparatus a trajectory of charged particles is parallelized with a deviation angle of ±1° or less so that the charged particles incident on the planar collimator plate are approximately perpendicular to said plate.