First Demonstration of Sub-femtosecond X-ray Pulses at SwissFEL

We have produced ultra-short X-ray FEL pulses at SwissFEL by strongly compressing low-charge electron beams.  Single-shot spectral measurements with only a single mode (see the figure below) indicate a pulse duration well below one femtosecond (detailed analysis on the exact pulse duration is ongoing). There is a continuing effort to improve the performance of these short pulses in terms of stability and pulse energy. The generation of sub-femtosecond X-ray FEL pulses fulfills an important milestone for SwissFEL. Such pulses will allow the observation of matter with time and spatial resolutions on the atomic level, considering that an electron goes around a hydrogen atom in the order of 100 attoseconds (= 0.1 femtoseconds). This will make SwissFEL an invaluable tool for ultrafast science.