▎ 摘　　要

We theoretically study the efficiency and angular distribution of a graphene-plasmon excitation by an electron beam. An electron beam incident on doped graphene induces the out-of-plane transition radiation and in-plane plasmon-polariton waves. At the same time the electron loses its kinetic energy by energy conservation. From the momentum-resolved energy-loss spectrum, we can determine how much kinetic energy of the electron is converted into the transition radiation and plasmon-polariton excitation. Numerical results are presented by changing the incident angle and electron velocity. We find that the graphene plasmon polariton of particular frequency can be excited by an electron beam of appropriate velocity. Moreover, a deeply tilted incidence of the electron beam very efficiently excites the graphene plasmon polariton with an angular distribution range from -30 to 30 degrees. We also show that the transition radiation through graphene exhibits a peak at the threshold energy of the interband transition. These theoretical results are obtained under the local-response approximation of the optical conductivity as well as under the plasmon pole approximation. The results are also compared with those obtained in a thin metallic slab.