  Presently, the term transition radiation tends to denote a somewhat different
physical phenomenon than the original transition radiation discovered by J. E.
Lilienfeld in 1919, and re-employed in different forms again in 1953 and 1971.
Lilienfeld transition radiation is a subtle kind of radiation with distinctive
properties that may often be unexpected in prospect, yet is intuitive and
readily understood in retrospect. This paper distinguishes in clear terms
between the different kinds of transition radiation, and shows its link to
modern apparatus such as possible applications in the area of x-ray microscopy,
microholography, and the free electron laser .
