BEAMS
In the literature: open
Origin of the spectral pedestal in self-seeded hard X-ray FELs
In plain words
Self-seeding is supposed to make X-ray pulses of one clean color, but a broad background of extra colors remains. Its source has not been fully identified.
Precise statement
Hard X-ray self-seeded FELs show a broadband pedestal around the seeded line containing a sizable fraction of the energy. Determine the fractions due to residual SASE noise, sideband instability, electron-beam microbunching from the accelerator, and seed-crystal effects, and the minimum achievable pedestal fraction.
What would settle it
Spectral measurements with controlled microbunching and undulator taper, compared with 3D FEL simulations using measured electron phase space.