Inhomogeneous broadening effects in a multiharmonic wiggler based optical klystron

Multiharmonic wiggler based optical klystrons driven by a monoenergetic electron beam are known to be capable of producing a considerably higher gain than conventional optical klystrons. In this contribution, inhomogeneous broadening effects due to electron energy spread are considered for these multiharmonic optical klystrons. A modification to a recently developed convolution technique is derived to formulate the inhomogeneously broadened interaction gain in the small signal regime, taking account of the energy spread effects on electron bunching in the drift section. Based on the new gain formulation, numerical examples are used to demonstrate that the beam quality requirement of multiharmonic optical klystrons is essentially the same as that of their conventional counterparts. Thus for the same interaction gain, the gain enhancement achieved with a multiharmonic optical klystron configuration can be used to relax requirements for both the quality and current of the electron beam. In addition, it is suggested that the new formulation may be used to improve the accuracy of gain spectrum based techniques for beam quality measurement.