Photon beams probe in a unique manner the crystalline and electronic structure of matter on a variety of length scales and time.

The Helmholtz Association unites all major German synchrotron radiation sources with public user access. Furthermore, Helmholtz centres are at the forefront of free electron laser (FEL) developments. At present, four synchrotron radiation sources (ANKA, BESSY II, DORIS III, PETRA III) and one FEL (FLASH) are in operation serving a large and diverse user community with a wide spectrum of different techniques. In addition, the European XFEL is being constructed.

The image shows a single shot coherent diffractive image of an artificial test structure on a SiN-membrane at FLASH. On the inset you see the reconstructed object.

Synchrotron radiationsources provide well collimated high intensity photon beams from the Terahertz to the hard X-ray regime. Beams with selectable circular polarization revolutionised the investigation of magnetic properties. Depending on the wavelength, the experiments can be made surface, interface or bulk sensitive and can probe samples under special environments. The coherent fraction of the X-ray beams allows for high resolution holography and micro-tomography of the target, whereas dynamics can be studied by intensity correlation spectroscopy. The very high intensity in focal spots down to the nm range enables the investigation of extremely small sample volumes and of matter under extreme conditions.

Compared to the best synchrotron radiation sources, X-ray free-electron lasers (FEL) provide a gain of 4 and 9 orders of magnitude in average and peak brilliance, respectively. Beams are coherent and a pulse length of the order of 50-100 fs allows for the investigation of excited and short lived intermediate states, i.e. real time observations of dynamics. The coherence properties of FELs enable totally new techniques to study complex samples.