The basic theory of free-electron lasers (FELs) indicates that the output wavelength of a seeded FEL operated in the high-gain harmonic generation (HGHG) configuration is determined by the wavelength of the seed laser and light is emitted when the undulators are tuned to an exact harmonics of the seed laser. In a realistic case. when taking into account the electron beam imperfections... https://www.jmannino.com/save-now-3D-Key-Ring-Rainbow-Lorikeet-Pete-Cromer-Wilmot-Harvey-super-grab/