A new monochromator with multiple offset cylindrical lenses 2: Aberration analysis and its applications

Abstract

In this article, we continue our investigation and offer a complementary discussion of our newly proposed monochromator (MC). It consists of multiple offset cylindrical lenses and achieves high performance with a simple structure. We simulate beam profiles in an extensive current range by means of a ray trace method. Through a multiple regression analysis, we derive the aberrations of the MC up to the third rank. The second-order aperture aberration and lateral energy dispersion are canceled on the exit image plane, which is a crucial condition when MCs are applied to electron microscopes. These aberrations enable the interpretation of the beam profiles for various currents and energy deviations. In addition, they provide the dependencies pertaining to the MC performance, such as the energy spread and brightness, of beam currents for various source conditions. This information is essential to implement the MC onto an electron microscope. By improved the spatial resolutions and energy resolutions, the microscope can reveal new information about various specimens. In addition, the simple and robust structure of the MC will satisfy the demand from industry. Additionally, this study contributes to charged particle optics theory in that it presents a practical example of aberration computation, of which the optics is too complicated to establish aberration integrals, through the ray trace method and regression analysis.