Abstract
This book presents the theory of quadrupole focusing with the practical development of microprobe systems in mind. The introductory chapter outlines the analytical processes and provides a background to the problems of designing quadrupole probe-forming systems. Following a description of the quadrupole lens and the mathematical models used to describe the fields within both magnetic and electrostatic quadrupole lenses, the authors describe two techniques for calculating the path of a charged particle through a beam-optical system; matrix methods and numerical raytracing. The minimum spot size achieved by a quadrupole system is influenced strongly by parasitic aberrations due to imperfections in the construction and alignment of the instrument. The authors assess the importance of the various effects by reference to their influence in three existing microprobe systems. Finally, they describe briefly some novel and interesting alternatives to the quadrupole lens as the focusing element. Refs.