Synchrotron Radiation / Free-electron lasers
Synchrotron radiation arises when energetic electrons are accelerated, for example, by being forced to travel in a curved path by bending magnets or special magnetic structures known as wigglers and undulators of the DORIS III or PETRA III storage rings at the Hamburg Synchrotron Radiation Laboratory (HASYLAB). The radiation produced possesses many properties which simply cannot be achieved using conventional radiation sources such as rare gas discharge lamps or X-ray tubes. Synchrotron radiation opens up a wealth of new research possibilities in all areas of natural science.
Angle-resolved photoemission spectroscopy excited with synchrotron radiation is the most powerful tool for probing the electronic structure of atoms, molecules, clusters and solids. Our Angular Spectrometer for Photoelectrons with High Energy REsolution (ASPHERE) is used at two beamlines at HASYLAB delivering synchrotron light between 10 eV and 40 eV (HONORMI) or between 40 eV and 1500 eV (BW3).
'Fourth-generation' synchrotron light sources, based on free-electron lasers are currently under development (FLASH, X-FEL), that will be capable of producing light of such extreme brilliance that new ways of focusing the radiation will have to be found. We are working on the development of new X-ray optics, based on the simple concept of an array of pinholes. The 'photon sieve' exploits the monochromaticity and coherence of light from an free-electron laser to focus soft X-rays with unprecedented sharpness. The combination of sharper focus with extreme brightness should herald a new era of photoelectron spectroscopy combining highest spatial, angular and energy resolution.
Figure 1: Side view of the experimental setup at the BW3 beamline guiding the monochromatized synchrotron radiation to our photoelectron spectrometer ASPHERE (picture from S. Woedtke, Ph.D. thesis).