Crossed ponderomotive lenses for spherical aberration correction in electron optics

This article evaluates the lens characteristics of a nonrotationally symmetric electron lens based on a ponderomotive potential, i.e., a ponderomotive lens, formed by intersecting one or more optical beams perpendicular to an electron beam. Based on geometric optics, design formulas are derived for the focal length and general spherical aberration coefficients of specifically crossed ponderomotive lenses. Numerical calculations demonstrate that a pair of these crossed ponderomotive lenses can effectively correct spherical aberration in the objective lens of an electron microscope. Unlike rotationally symmetric ponderomotive lenses, which require the optical beam to be coaxially aligned with the electron beam, the crossed ponderomotive lens avoids the need to place optical mirrors and lenses directly on the beam axis. Thus, it offers practical advantages in designing and building electron optical instruments and contributes to system miniaturization. With lens properties similar to multipole lenses, the proposed crossed ponderomotive lens is expected to facilitate diverse developments in electron optical systems incorporating ponderomotive potentials.