Demonstration of two-color x-ray free-electron laser pulses with a sextupole magnet

We present measurements of two-color x-ray free electron laser (FEL) pulses generated with a novel scheme utilizing a sextupole magnet. The sextupole, in combination with a standard orbit control tool, is used to suppress the radiation from the bunch core, while keeping the head and the tail of the beam lasing, each at a different photon energy. The method is simple, cost-effective and applicable at any repetition rate. We demonstrate the tunability of the scheme and discuss its advantages and practical limitations.