1. Emma, P., Akre, R., Arthur, J., Bionta, R., Bostedt, C., et al.: Nat. Photonics 4, 641 (2010)
2. Bostedt, Ch., Boutet, S., Fritz, D.M., Huang, Z., Lee, H.J., et al.: Rev. Mod. Phys. 88, 015007 (2016)
3. Materlik, G., Tschentscher, Th. (eds.): TESLA technical design report. Part V. The X-ray free electron laser. http://tesla.desy.de/new_pages/TDR_CD/PartV/fel.html (2001)
4. http://flash.desy.de/
5. LCLS web site: https://slacportal.slac.stanford.edu/sites/lcls_public/Pages/Default.aspx