Observation of harmonic lasing in the Angstrom regime at European X-ray Free Electron Laser

Harmonic lasing provides an opportunity to extend the photon energy range of existing and planned x-ray free electron laser (FEL) user facilities. Contrary nonlinear harmonic generation, can generate a much more intense, stable, narrow-band FEL beam. Another interesting application is self-seeding that allows improve longitudinal coherence spectral power self-amplified spontaneous emission FEL. This concept was tested at soft facility FLASH in 4.5--15 nm Pohang accelerator laboratory X-ray Free Electron Laser (XFEL) 1 nm. In this paper we present recent results from European XFEL where successfully demonstrated 5.9 Angstrom 2.8 Angstrom. latter case obtained both third fifth and, for first time, operated cascade (fifth-third-first harmonics undulator). These pave way reaching very high energies, up 100 keV.