Virtual dielectric waveguide mode description of a high-gain free-electron laser.II. Modeling and numerical simulations

摘要

A high-gain free-electron laser is modeled using an expansion of the radiation field in terms of guidedLaguerre-Gaussian modes of a virtual dielectric waveguide [E. Hemsing, A. Gover, and J. Rosenzweig, pre-ceding paper, Phys Rev. A 77, 063830 (2008)]. The radiation profile evolution, power gain, and detuningefficiency characteristics are investigated for seeding with fundamental Gaussian and higher-order Laguerre-Gaussian input modes on a Gaussian e-beam in the collective regime. The full wave evolution solution atdifferent seed radiation injection conditions results in determination of the optimal waist size and waist positionof the seed radiation beam for maximum power coupling efficiency. Results for guided mode evolution andpower gain are shown to be consistent with simulations performed with the code GENESIS 1.3. The amplifica-tion and spontaneous generation of FEL radiation with orbital angular momentum is also considered.