Induced Channeling Process in a Crystal

Abstract

It is known that due to the relativistic motion of a charged particle in a crystal, an exotic situation takes place when the effective potential of the crystal planes or axes becomes a potential well for the particle in the transverse direction with respect to its initial motion, and so-called channeling of the particle occurs accompanied by spontaneous channeling radiation. The channeling radiation of ultrarelativistic electrons and positrons in a crystal is of great interest for two major reasons: the radiation is in the shortwave region (X-ray and $\gamma$-ray domains) and its spectral intensity considerably exceeds that of the other types of radiation in this range of frequencies. Induced channeling radiation in the presence of an external coherent radiation field becomes important as a potential source for shortwave coherent radiation, which may be considered as a version of a free electron laser . As a periodic system with high coherency and owing to the similar periodic character of particle motion, the crystal channel may be compared with an undulator—it is a “micro-undulator” with the space period much smaller than that of an undulator. On the other hand, the particle–external coherent EM wave interaction process in the channel of a crystal proceeds with the inverse stimulated effect reducing the particle acceleration and other classical and quantum coherent effects. Hence, this chapter will consider the induced channeling process with regard to general aspects of coherent interaction of relativistic electrons and positrons with a plane transverse EM wave in a crystal.