Interaction of short-wavelength free-electron laser (FEL) beams with matter is undoubtedly a subject to extensive investigation in last decade. During the interaction various exotic states of matter, such as warm dense matter, may exist for a split second. Prior to irreversible damage or ablative removal of the target material, complicated electronic processes at the atomic level occur. As energetic photons impact the target, electrons from inner atomic shells are almost instantly photo-ionized, which may, in some special cases, cause bond weakening, even breaking of the covalent bonds, subsequently result to so-called non-thermal melting. The subject of our research is ablative damage to lead tungstate (PbWO4) induced by focused short-wavelength FEL pulses at different photon energies. Post-mortem analysis of complex damage patterns using the Raman spectroscopy, atomic-force (AFM) and Nomarski (DIC) microscopy confirms an existence of non-thermal melting induced by high-energy photons in the ionic monocrystalline target. Results obtained at Linac Coherent Light Source (LCLS), Free-electron in Hamburg (FLASH), and SPring-8 Compact SASE Source (SCSS) are presented in this Paper.

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Vojtech Vozda, Pavel Boháček, Tomáš Burian, Jaromir Chalupský, Vera Hájková, Libor Juha, Ludek Vyšín, Jérôme Gaudin, Philip A. Heimann, Stefan P. Hau-Riege, Marek Jurek, Dorota Klinger, Jacek Krzywinski, Marc Messerschmidt, Stefan P. Moeller, Robert Nagler, Jerzy B. Pelka, Michael Rowen, William F. Schlotter, Michele L. Swiggers, Harald Sinn, Ryszard Sobierajski, Kai Tiedtke, Sven Toleikis, Thomas Tschentscher, Joshua J. Turner, Hubertus Wabnitz, Art J. Nelson, Maria V. Kozlova, Sam M. Vinko, Thomas Whitcher, Thomas Dzelzainis, Oldrich Renner, Karel Saksl, Roland R. Fäustlin, Ali R. Khorsand, Marta Fajardo, Bianca S. Iwan, Jakob Andreasson, Janos Hajdu, Nicusor Timneanu, Justin S. Wark, David Riley, Richard W. Lee, Mitsuru Nagasono, and Makina Yabashi, "Non-thermal damage to lead tungstate induced by intense short-wavelength laser radiation (Conference Presentation)," Proc. SPIE 10236, Damage to VUV, EUV, and X-ray Optics VI, 102360G (Presented at SPIE Optics + Optoelectronics: April 25, 2017; Published: 21 June 2017); https://doi.org/10.1117/12.2270944.5463398567001.