What bandwidth limitations are you referencing? My understanding is that deep euv lithography is limited by chromatic aberration, so the narrow bandwidth of a single beam FEL would be an advantage. If you need more bandwidth, you can chirp it. Is the bandwidth too high?
They mean bandwidth as in rate at which one can expose a mask using an electron beam, because they’ve confused two different technologies. See my other reply.
P.S. Can you usefully chirp an FEL? I don’t know whether the electron sources that would be used for EUV FELs can be re-tuned quickly enough, nor whether the magnet arrangements are conducive to perturbing the wavelength. But relativistic electron beams are weird and maybe it works fine. Of course, I also have no idea why you would want to chirp your lithography light source.