teaching and education Synchrotron radiation and X-ray free-electron lasers (X-FELs) explained to all users, active and potential ISSN 1600-5775 Yeukuang Hwua,b,c* and Giorgio Margaritondod* aInstitute of Physics, Academia Sinica, Taipei 11529, Taiwan, bDepartment of Engineering Science, National Cheng Kung University, Tainan 70101, Taiwan, cBrain Research Center, National Tsing Hua University, Hsinchu 30013, Taiwan, and dFaculte´ des Sciences de Base, Ecole Polytechnique Fe´de´rale de Lausanne, 1015 Lausanne, Switzerland. Received 8 September 2020 *Correspondence e-mail:
[email protected],
[email protected] Accepted 29 March 2021 Synchrotron radiation evolved over one-half century into a gigantic worldwide Edited by M. Yamamoto, RIKEN SPring-8 enterprise involving tens of thousands of researchers. Initially, almost all users Center, Japan were physicists. But now they belong to a variety of disciplines: chemistry, materials science, the life sciences, medical research, ecology, cultural heritage Keywords: synchrotron; X-FEL; relativity; and others. This poses a challenge: explaining synchrotron sources without ponderomotive. requiring a sophisticated background in theoretical physics. Here this challenge is met with an innovative approach that only involves elementary notions, commonly possessed by scientists of all domains. 1. Background Synchrotron radiation sources and free-electron lasers (Margaritondo, 1988, 2002; Winick, 1995; Willmott, 2011; Mobilio et al., 2015; Bordovitsyn, 1999) are, arguably, the most important practical applications of Albert Einstein’s special relativity (Rafelski, 2017). Indeed, they exploit relativistic properties to produce electromagnetic radiation in spectral ranges where other emitters are unsatisfactory, most notably X-rays. Explaining such sources to non-physicists is not easy. We propose here an approach that only requires a few basic scientific notions.