Microwave-induced control of free-electron-laser radiation - art. no. 026505

The dynamical response of a relativistic bunch of electrons injected in a p lanar magnetic undulator and interacting with a counterpropagating electrom agnetic wave is studied. We demonstrate a resonance condition for which the free-electron-laser (FEL) dynamics is strongly influenced by the presence of the external field. It opens up the possibility of control of short wave length FEL emission characteristics by changing the parameters of the micro wave field without requiring change in the undulator's geometry or configur ation. Numerical examples, assuming realistic parameter values analogous to those of the TTF-FEL, currently under development at DESY, are given for p ossible control of the amplitude or polarization of the emitted radiation.