In radio astronomy, the theory of synchrotron emission by relativistic electrons spiraling in magnetic fields assumes that electrons radiate singly, so power scales with number of electrons. Yet in many astrophysical environments this is not so, and recently jets from active galactic nuclei show very high luminosity, inconsistent with plausible single-particle synchrotron emission. Laboratory experiments show that by stimulating plasma instabilities with relativistic electron beams, one can induce increases in both synchrotron and Compton-boosted spectral emission by factors of ~ 10^6. Enhancement presumably arises from coherent bunching of the relativistic electrons as they spiral in an ambient magnetic field. Higher frequency emission can come from coherent scattering of electrons by "cavitons" of compressed Langmuir waves. Both these mechanisms reveal facets in the laboratory which may be relevant to astrophysical environments, affecting both their brightness and their polarization.