Theory of Nonlinear Harmonic Generation in Free-Electron Lasers with Helical Wigglers

Abstract

Coherent Harmonic Generation (CHG), and in particular Nonlinear Harmonic Generation (NHG), is of importance for both short wavelength Free-Electron Lasers (FELs), in relation with the achievement of shorter wavelengths with a fixed electron-beam energy, and high-average power FEL resonators, in relation with destructive effects of higher harmonics radiation on mirrors. In this paper we present a treatment of NHG from helical wigglers with particular emphasis on the second harmonic. Our study is based on an exact analytical solution of Maxwell's equations, derived with the help of a Green's function method. In particular, we demonstrate that nonlinear harmonic generation (NHG) from helical wigglers vanishes on axis. Our conclusion is in open contrast with results in literature, that include a kinematical mistake in the description of the electron motion.

arXiv comment23 pages, 4 figures

References in corpus (2)

• Undulator Radiation in a Waveguide
• Fourier Optics treatment of Classical Relativistic Electrodynamics

Cited by in corpus (3)

• VUV and X-ray coherent light with tunable polarization from single-pass free-electron lasers
• Longitudinal impedance and wake from XFEL undulators. Impact on current-enhanced SASE schemes
• Angular Distribution of Nonlinear Harmonic Generation in Helical Undulators: a comparison between experiments and theory