Abstract

When fast electrons pass through a periodic medium, electromagnetic wave is generated (resonant transition radiation)¹. The angle of emission θ with respect to the beam and wavelength λ for this radiation is related by $\sqrt{\overline{ϵ}}\cos \theta =c/v-n\lambda /l$ where $\overline{ϵ}$ is the average dielectric constant, v is the velocity of electron, n is an integer, and l is the spatial period of interfaces. We consider a system composed of many thin (≤100 Å) layers which makes it possible to drastically reduce the critical energy to a few tens Kev or lower ²,³. The use of lower energy is prevented by the scattering of electrons and absorption of X-ray photon in the material. Taking these two factors into consideration, we obtain the optimal range of electron energy E_o (which appears to be between a few hundreds Kev and a few Mev), the total thickness of the superlattice L and maximal radiation for a given frequency ω.

© 1986 Optical Society of America