Published online by Cambridge University Press: 05 August 2012
Fifty years ago devices employing charged-particle beams were confined to the purview of a small group of physicists studying elementary processes. Today chemists, biologists, and engineers employ beams of ions or electrons to probe various materials and to investigate discrete processes. Physicists are constructing beam machines to control the momentum of interacting particles with energies from a few tenths of an electron volt to trillions of electron volts. Chemists routinely use mass spectrometers as analytical tools and various electron spectrometers to probe molecular structures. The electron microscope is one of the primary tools of the modern biologist. Furthermore charged-particle beam technology has spread to industry, where electron-beam machines are used for cleaning surfaces and welding, and ion-beam devices are used in the preparation of semiconductors.
The properties of charged-particle beams are analogous in many respects to those of photon beams: hence the appellation charged-particle optics. In the following sections the laws of geometrical optics will be covered insofar as they apply to charged-particle beams. The consequences of the coulombic interaction of charged particles will be considered. In addition we shall discuss the design of electron and ion sources, as well as the design of electrodes that constitute optical elements for manipulating beams of charged particles. We shall consider primarily electrostatic focusing by elements of cylindrical symmetry and restrict discussion to particles of sufficiently low kinetic energies that relativistic effects can be ignored.