Coherent Absorption and Emission Processes of Energetic Particles Penetrating Crystals

Abstract

Swift charged particles moving through an ordered array of atoms in a crystal experience periodic perturbations which can give rise to coherent absorption or emission of photons. Indeed the phenomenon of coherent bremsstrahlung arising from ultrarelativistic electron penetration of crystals has been studied for many years.¹ The complexity of the Fourier components of the electric field experienced by the particle is greatly reduced if the direction of motion lies along a crystal axis or in a crystal plane. Here, however, the motion of the particle may be governed by correlated collisions with the atomic rows or planes and the particle is said to be “channeled.” In this case another periodicity is involved in the motion and transitions between bound states in the transverse motion can lead to radiation of another type which has been dubbed “channeling radiation.”