Effect of induced betatron motion on longitudinal wiggler free-electron laser gain

In this article, we discuss the modifications that occur in the brightness and gain of a longitudinal wiggler-free electron laser with the aid of induced betatron oscillation. Two novel approaches have been discussed to improve the gain of the system. In the first scheme, an auxiliary undulator field with betatron oscillations brings in additional bunching and results in enhanced gain. In the second scheme, an axial magnetic field is tuned to provide additional bunching for gain enhancement.