An array of spatially separated beamlets is produced by a corresponding array of charged particle emitters. Each emitter is at an electrostatic potential difference with respect to an immediately adjacent emitter in the array. The beamlets are converged laterally to form an charged particle beam. The beam is modulated longitudinally with infrared radiation to form a modulated beam. The charged particles in the modulated beam are bunched longitudinally to form a bunched beam. The bunched beam may be modulated with an undulator to generate a coherent radiation output. This abstract is provided to comply with rules requiring an abstract that will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.