Author Affiliations

Praveen K. Maroju,¹ Matteo Moioli,¹ Dominik Ertel,¹ Hamed Ahmadi,¹ Giuseppe Sansone,¹ Cesare Grazioli,² Michele Di Fraia,³ Oksana Plekan,³ Paola Finetti,³ Enrico Allaria,³ Luca Giannessi,³ Carlo Spezzani,³ Giuseppe Penco,³ Simone Spampinati,³ Alexander Demidovich,³ Miltcho Danailov,³ Roberto Borghes,³ Georgios Kourousias,³ Carlos Eduardo Sanches Dos Reis,³ Fulvio Billé,³ Kevin C. Prince,³ Carlo Callegari,³ Giovanni De Ninno,⁴ A. Lutman,⁵ Richard J. Squibb,⁶ Raimund Feifel,⁶ Paolo Carpeggiani,⁷ Tommaso Mazza,⁸ Michael Meyer,⁸ Samuel Bengtsson,⁹ Neven Ibrakovic,⁹ Emma Rose Simpson,⁹ Johan Mauritsson,⁹ Tamás Csizmadia,¹⁰ Mathieu Dumergue,¹⁰ Sergei Kühn,¹⁰ N.G. Harshitha,¹⁰ Daehyun You,¹¹ Kiyoshi Ueda,¹¹ Marie Labeye,¹² Jens Egebjerg Bækhøj,¹² Kenneth J. Schafer,¹² Elena V. Gryzlova,¹³ and Alexei N. Grum-Grzhimailo¹³

¹Physikalisches Institut, Albert-Ludwigs-Universität Freiburg Hermann-Herder-Straße 3, 79104 Freiburg, Germany

²ISM-CNR, Trieste LD2 Unit, Basovizza AREA Science Park, Trieste, I-34149, Italy

³Elettra-Sincrotrone Trieste, 34149 Basovizza, Trieste, Italy

⁴Elettra-Sincrotrone Trieste, 34149 Basovizza, Trieste, Italy; Laboratory of Quantum Optics, University of Nova Gorica, 5001 Nova Gorica, Slovenia

⁵SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA

⁶Department of Physics, University of Gothenburg, Origovagen ¨ 6B, 412 96 Gothenburg, Sweden

⁷Technische Universität Wien, Austria

⁸European XFEL, Holzkoppel 4, 22869 Schenefeld, Germany

⁹Department of Physics, Lund University, PO Box 118, SE-221 00 Lund, Sweden

¹⁰ELI-ALPS, ELI-Hu Kft., Dugonics tér 13, H-6720 Szeged Hungary

¹¹Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan

¹²Department of Physics and Astronomy Louisiana State University Baton Rouge, Louisiana 70803-4001, USA

¹³Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Moscow 119911, Russia