Speaker
Description
In echo-enabled harmonic generation, adjacent harmonics naturally carry comparable microbunching amplitudes. We investigate how coherent–synchrotron–radiation–induced gain shaping, controlled transverse structure in the seed lasers, and polarization tuning, tapering, and detuning of the radiators can be used to steer these neighboring harmonics into different FEL eigenmodes. Under suitable conditions, this allows two nearby wavelengths to achieve comparable output power, with one harmonic lasing in an off-axis annular mode. At the same time, the other produces the familiar on-axis Gaussian mode characteristic of externally seeded FELs. Such a tunable, multimodal, multi-color configuration may be directly valuable for a broad range of user experiments. This work is supported by start-to-end simulations using realistic soft-X-ray FEL parameters. Finally, we discuss potential applications of such a scheme at high-repetition-rate seeded FELs, such as Free-Electron LASer in Hamburg (FLASH), where stable dual-color, multimode operation could expand experimental capabilities.
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