Novel possibilities for coherent radiation sources

Higher frequency radiation sources and their detectors have many potential uses - especially if they are compact, variable, efficient and have high brightness. We discuss some possibilities together with various impediments to their realization. The differences between bound and free electrons are studied from the standpoint of the frequencies that are practicably achievable. With the ansatz that the transport physics with Maxwell´s equation are valid but modified by the material properties, a number of analogs exist between these two basic sources of radiation. In many cases, the differences are between macro and micro implementations e.g. between klystron and klystrinos (micro or nano) or solid state and semiconductor lasers or rare-earth doped transistors. Cases with no apparent analogs are ones due to unique quantum effects e.g. radiation at 3kT_c in superconductors. This is well above magnetic resonance imaging MRI around 0.4 μeV but well known below room temperature at 25 meV. Bound and free possibilities for planar, micro undulators over this range are studied using FDTD techniques. To our knowledge, there have been no implementations of either possibility.