Experimental demonstration of mode-coupled and high-brightness SASE in an x-ray FEL

This contribution will present the first experimental demonstration of two schemes that enhance the longitudinal coherence of SASE X-ray FEL pulses: 1) mode-coupled SASE, which results in frequency combs with tunable peak separation; and 2) high-brightness SASE, producing FEL pulses with a bandwidth reduction up to a factor of three with respect to SASE. Both schemes are based on delaying the electron beam with magnetic chicanes placed within the undulator. The demonstration has been carried out at the soft X-ray beamline of SwissFEL for photon energies between 500 and 600 eV. This work will benefit current FEL applications and may open up new research areas requiring frequency combs or narrow bandwidths.