ABSTRACT
This chapter discusses only a few fundamental problems concerning transition radiation and transition scattering. The radiation emitted forwards, particularly when the charge moves from a medium into a vacuum, has a higher-frequency spectrum and, for instance, in a condensed medium the transition radiation from relativistic particles can lie in the X-ray frequency range. The effect of transition radiation has many aspects, but until recently researchers have concentrated on the radiation emitted by a source crossing one or several boundaries between media. Transition scattering plays an important role in plasma physics, and on the whole it is a fairly general effect. For example, transition scattering must take place in a vacuum when an electromagnetic or gravitational wave is incident on a region with a strong static electromagnetic field. The general theory describing the scattering of arbitrary waves in a medium must therefore take transition scattering into account.
