The European Cluster of Advanced Laser Light sources (EUCALL) was a European Union-funded project which grouped most accelerator- and laser-driven X-ray research infrastructures (RIs) in Europe, operated for use by the wider scientific communities, so-called user facilities. Researchers from diverse science disciplines perform investigations using these facilities, leading to new scientific know-how, materials and, possibly, to new products. Europe has a leading position worldwide in Photon Science applications and technology, and the overall network of accelerator- and laser-driven user RIs is one fundament of this position. The overlap between optical lasers and accelerator-based X-ray light sources had been limited due to differences in their properties and their applications. Optical lasers are now so powerful that they can drive sources of X-rays and this community now builds and operates large RIs providing these secondary X-ray sources to users. At the same time, the development of accelerator-driven X-ray free-electron lasers now allow the generation of X-rays with laser properties, enabling to apply experimental techniques which until recently only where available for the (near-)visible spectrum using laser sources. Both of these developments started to fill a longstanding gap between the laser- and accelerator-based RIs.
Within EUCALL, accelerator- and laser-based RIs cooperated for the first time on common technical, scientific, and strategic issues, with the goal to make the future operation of these facilities more efficient, and therefore more sustainable. EUCALL developed solutions to technology and operation needs common to these RIs. Examples of technology developments within EUCALL include new standardized sample holders, new sensors and detectors for X-ray beams, new computer software to fully simulate experiments at the various light sources, and new schemes for ultrafast data transfer for experiments at the RIs. EUCALL developed methods and processes and enabled an exchange of know-how between the facilities, which together will enable the RIs, and also the wider light source communities, to better exploit the great research and innovation potential that these RIs provide. Through its results, EUCALL further harmonized the landscape of both classes of photon science RIs in Europe and beyond.