The first free electron lasers were built in the 1970s and produced infrared and later visible and ultraviolet light. In order to make FELs work for shorter wavelengths, in particular for X-rays, the technology was further developed during the 1990s culminating in the first demonstration of a single-pass FEL in the vacuum ultraviolet (VUV) around 100 nm wavelength in 2000 - 2002 at DESY, Hamburg. Based on these developments DESY proposed to construct a large FEL facility for hard X-rays. This proposal resulted in the European XFEL. The test facility at DESY was extended and converted to what is now known as the FLASH facility; it has been in routine user operation since 2005.
The successful proof-of-principle experiments triggered also a number of other new FEL projects worldwide. The Linac Coherent Light Source (LCLS) at SLAC, Stanford, USA, was funded and demonstrated for the first time perfect, stable operation at hard X-ray wavelengths in 2009. A new X-ray FEL (SACLA) was built in Japan; first lasing was achieved in 2011, user operation started in 2012. Another X-ray FEL is under construction in Pohang, Korea. In Europe, the FERMI@Elettra project near Trieste, Italy, has been realised, starting operation in 2011 as the first seeded FEL in the VUV to soft X-ray range, and the SwissFEL project at PSI, Villigen, Switzerland, is under construction.
Since FELs are unique light sources combining the properties of synchrotrons and conventional lasers, their scientific applications are broad and diverse, thus requiring a number of complementary beam lines and a large variety of experimental stations. On the other hand, FELs are lasers and can serve only a single experiment at a time. Consequently, a set of several, more or less complementary FEL light sources are required in order to exploit their scientific potential in an efficient way. The new research opportunities and the challenges of creating such a research infrastructure of free electron lasers in Europe were also discussed by the newly established European Strategy Forum on Research Infrastructures (ESFRI) and led to including two FEL projects in the first ESFRI roadmap: the European XFEL as a single-site facility and IRUVX-FEL (later called EuroFEL) as an additional consortium of national FEL facilities (ESFRI Report 2006).
From 2005 – 2007, the EUROFEL Design Study project http://www.eurofel.org was funded by the European Commission under FP6. This project brought together all interested parties in Europe (16 institutions) including research centres and relevant University institutes to develop the most critical technology needed for the construction and operation of the novel FEL user facilities. It was the enthusiastic start of joint research and development activities in this field coordinated on the European level.
Under FP7, both ESFRI projects received funding for preparatory phase projects: The Pre-XFEL project (July 2007 – June 2011, http://www.xfel.eu/project/pre_xfel/) supported the foundation of the European XFEL GmbH company. This included mainly the provision of technical, legal and financial documents necessary for the foundation of the company, the immediate recruitment of international staff, and the mobilisation and stimulation of the potential user community. The IRUVX-PP project (April 2008 – March 2011, http://www.iruvx.eu/e20) focused on the preparation of a future EuroFEL consortium, led by the key questions: How can we make sure that the scientific potential of free electron lasers can be fully exploited in Europe? How can we exploit the complementary features and expertise of the individual member facilities and maximise the benefits for both the member facilities and the users? What are the areas in which the partners should collaborate, what are the specific activities and the benefits for the stakeholders, and what kind of structure should the consortium have in order to achieve the best results?
At the end of IRUVX-PP, the collaboration continued under a memorandum of understanding (MoU) and was expanded to include the European XFEL. This MoU was signed on the 31 May 2012 by Elettra and INFN (Italy), European XFEL, DESY and HZB (Germany) , MAX IV (Sweden), NCBJ (Poland), PSI (Switzerland), SOLEIL (France), and STFC (United Kingdom). The membership has further increased to 14, with the admission of Ankara University (Turkey), CNRS (France), HZDR (Germany) and Radboud University (The Netherlands). These members agreed at the beginning of 2014 to continue the collaboration under the name "FELS OF EUROPE".