Cathodoluminescence of ruby as a function of angle of incidence

The effect is explained in terms of an increase in efficiency with angle of incidence. Inclined excitation is proposed as a method of preventing charging of the surface.We are indebted to Professor V. L. Levshin for discussions, to A. G. Dvchinnikov for assistance in making the attachment, and to Yu. V. Khrushchev for assistance in the experiments.