AES Instrumentation: Magnetic Lenses

Magnetic lenses are often used in electron optics to avoid the high voltages required by electrostatic lenses. Magnetic lenses have rotational symmetry with the radial component of the magnetic field equal to zero along the lens axis. Charged particles traveling on the axis are not deflected by the lens. Charged particles travelling parallel to the axis are deflected across the axis at the focal point. The focal point can be adjusted by changing the current in the magnet windings. Magnetic lenses are often asymmetric along the rotational axis. This provides space for deflectors, stigmators, and apertures behind the lens. Electron columns use an asymmetric lens to demagnify the electron beam to its final spot size (2 to 200 nm).

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