Improved Generation of Higher Harmonics and Suppression of the Lowest Harmonics in an X-Ray FEL with a Two-Frequency Undulator

Abstract

Theoretical research and simulation of the suppression of the lowest harmonics of free-electron laser radiation (FEL) with a two-frequency undulator was carried out. A phenomenological model of an FEL that describes the evolution of power in an FEL considering all the main losses was used. Radiation of harmonics in an FEL with a two-frequency flat undulator is compared with the radiation of harmonics in an FEL with an ordinary flat undulator. Radiation of harmonics and the FEL-induced energy spread in a single-pass FEL, where harmonics that are lower with respect to the nth harmonic are suppressed, for example, by a shift of the electron phase relative to photons by kπ/n, k = even, between the undulator walls were investigated. The advantages of using a two-frequency undulator in an FEL with suppressed lowest harmonics and the possibility of generating high-power X-ray radiation of higher harmonics in a linear mode are illustrated. The power of the higher harmonics can exceed the pitch power of an ordinary FEL with a flat undulator.