Diffraction effects in directed radiation beams

A number of proposed applications of electromagnetic waves require that the radiation beam maintain a high intensity over an appreciable propagation distance. These applications include, among others, power beaming, advanced radar, laser acceleration of particles, and directed-energy sources. The quest to achieve these objectives has led to a resurgence of research on diffraction theory. We present a survey and critique of the analyses and experimental tests of solutions of the wave equation in connection with so-called diffractionless and other directed radiation beams. The examples discussed include electromagnetic missiles, Bessel beams, electromagnetic directed-energy pulse trains, and electromagnetic bullets.