The growth and saturation of spontaneous emission and coherent radiation in a long undulator are studied by use of the 3D Maxwell-Klimontovich equation. Electron correlation, transverse radiation profiles, spectral features, transverse coherence, and intensity characteristics are discussed. The results, which agree with recent microwave experiments, are applied to proposed schemes for generation of short-wavelength coherent radiation.

• Received 28 April 1986

DOI:https://doi.org/10.1103/PhysRevLett.57.1871