Effects of Finite Larmor Radius on Small Signal Free Electron Laser With a Staggered Undulator

In this article, the theory of the spectral properties of undulator radiation and the free electron laser (FEL) gain in staggered undulator has been discussed. The important contributions of the pole-to-pole gap parameter and the finite larmor radius effects of the electron are included in the analysis. A finite electron larmor radius of the electron introduces azimuthal bunching through cyclotron motions and the axial electron bunching degrades. The interaction of the electron and the electromagnetic wave is driven away from the resonance and causes reduction in the FEL gain. An estimate of the gain reduction is presented through an analytical calculation.