2018-8-3, Sauppe, Mario, Rompotis, Dimitrios, Erk, Benjamin, Bari, Sadia, Bischoff, Tobias, Boll, Rebecca, Bomme, Cédric, Bostedt, Christoph, Dörner, Simon, Düsterer, Stefan, Feigl, Torsten, Flückiger, Leonie, Gorkhover, Tais, Kolatzki, Katharina, Langbehn, Bruno, Monserud, Nils, Müller, Erland, Müller, Jan P., Passow, Christopher, Ramm, Daniel, Rolles, Daniel, Schubert, Kaja, Schwob, Lucas, Senfftleben, Björn, Treusch, Rolf, Ulmer, Anatoli, Weigelt, Holger, Zimbalski, Jannis, Zimmermann, Julian, Möller, Thomas, Rupp, Daniela

Extreme ultraviolet (XUV) and X-ray free-electron lasers enable new scientific opportunities. Their ultra-intense coherent femtosecond pulses give unprecedented access to the structure of undepositable nanoscale objects and to transient states of highly excited matter. In order to probe the ultrafast complex light-induced dynamics on the relevant time scales, the multi-purpose end-station CAMP at the free-electron laser FLASH has been complemented by the novel multilayer-mirror-based split-and-delay unit DESC (DElay Stage for CAMP) for time-resolved experiments. XUV double-pulses with delays adjustable from zero femtoseconds up to 650 picoseconds are generated by reflecting under near-normal incidence, exceeding the time range accessible with existing XUV split-and-delay units. Procedures to establish temporal and spatial overlap of the two pulses in CAMP are presented, with emphasis on the optimization of the spatial overlap at long time-delays via time-dependent features, for example in ion spectra of atomic clusters.

2017-04-10, Savelyev, Evgeny, Boll, Rebecca, Bomme, Cédric, Schirmel, Nora, Redlin, Harald, Erk, Benjamin, Düsterer, Stefan, Müller, Erland, Höppner, Hauke, Toleikis, Sven, Müller, Jost, Kristin Czwalinna, Marie, Treusch, Rolf, Kierspel, Thomas, Mullins, Terence, Trippel, Sebastian, Wiese, Joss, Küpper, Jochen, Brauβe, Felix, Krecinic, Faruk, Rouzée, Arnaud, Rudawski, Piotr, Johnsson, Per, Amini, Kasra, Lauer, Alexandra, Burt, Michael, Brouard, Mark, Christensen, Lauge, Thøgersen, Jan, Stapelfeldt, Henrik, Berrah, Nora, Müller, Maria, Ulmer, Anatoli, Techert, Simone, Rudenko, Artem, Rolles, Daniel

In pump-probe experiments employing a free-electron laser (FEL) in combination with a synchronized optical femtosecond laser, the arrival-time jitter between the FEL pulse and the optical laser pulse often severely limits the temporal resolution that can be achieved. Here, we present a pump-probe experiment on the UV-induced dissociation of 2,6-difluoroiodobenzene (C6H3F2I) molecules performed at the FLASH FEL that takes advantage of recent upgrades of the FLASH timing and synchronization system to obtain high-quality data that are not limited by the FEL arrival-time jitter. We discuss in detail the necessary data analysis steps and describe the origin of the time-dependent effects in the yields and kinetic energies of the fragment ions that we observe in the experiment.

2018-8-2, Erk, Benjamin, Müller, Jan P., Bomme, Cédric, Boll, Rebecca, Brenner, Günter, Chapman, Henry N., Correa, Jonathan, Düsterer, Stefan, Dziarzhytski, Siarhei, Eisebitt, Stefan, Graafsma, Heinz, Grunewald, Sören, Gumprecht, Lars, Hartmann, Robert, Hauser, Günter, Keitel, Barbara, von Korff Schmising, Clemens, Kuhlmann, Marion, Manschwetus, Bastian, Mercadier, Laurent, Müller, Erland, Passow, Christopher, Plönjes, Elke, Ramm, Daniel, Rompotis, Dimitrios, Rudenko, Artem, Rupp, Daniela, Sauppe, Mario, Siewert, Frank, Schlosser, Dieter, Strüder, Lothar, Swiderski, Angad, Techert, Simone, Tiedtke, Kai, Tilp, Thomas, Treusch, Rolf, Schlichting, Ilme, Ullrich, Joachim, Moshammer, Robert, Möller, Thomas, Rolles, Daniel

The non-monochromatic beamline BL1 at the FLASH free-electron laser facility at DESY was upgraded with new transport and focusing optics, and a new permanent end-station, CAMP, was installed. This multi-purpose instrument is optimized for electron- and ion-spectroscopy, imaging and pump–probe experiments at free-electron lasers. It can be equipped with various electron- and ion-spectrometers, along with large-area single-photon-counting pnCCD X-ray detectors, thus enabling a wide range of experiments from atomic, molecular, and cluster physics to material and energy science, chemistry and biology. Here, an overview of the layout, the beam transport and focusing capabilities, and the experimental possibilities of this new end-station are presented, as well as results from its commissioning.

2018, Amini, Kasra, Savelyev, Evgeny, Brauße, Felix, Berrah, Nora, Bomme, Cédric, Brouard, Mark, Burt, Michael, Christensen, Lauge, Düsterer, Stefan, Erk, Benjamin, Höppner, Hauke, Kierspel, Thomas, Krecinic, Faruk, Lauer, Alexandra, Lee, Jason W. L., Müller, Maria, Müller, Erland, Mullins, Terence, Redlin, Harald, Schirmel, Nora, Thøgersen, Jan, Techert, Simone, Toleikis, Sven, Treusch, Rolf, Trippel, Sebastian, Ulmer, Anatoli, Vallance, Claire, Wiese, Joss, Johnsson, Per, Küpper, Jochen, Rudenko, Artem, Rouzée, Arnaud, Stapelfeldt, Henrik, Rolles, Daniel, Boll, Rebecca

We explore time-resolved Coulomb explosion induced by intense, extreme ultraviolet (XUV) femtosecond pulses from a free-electron laser as a method to image photo-induced molecular dynamics in two molecules, iodomethane and 2,6-difluoroiodobenzene. At an excitation wavelength of 267 nm, the dominant reaction pathway in both molecules is neutral dissociation via cleavage of the carbon-iodine bond. This allows investigating the influence of the molecular environment on the absorption of an intense, femtosecond XUV pulse and the subsequent Coulomb explosion process. We find that the XUV probe pulse induces local inner-shell ionization of atomic iodine in dissociating iodomethane, in contrast to non-selective ionization of all photofragments in difluoroiodobenzene. The results reveal evidence of electron transfer from methyl and phenyl moieties to a multiply charged iodine ion. In addition, indications for ultrafast charge rearrangement on the phenyl radical are found, suggesting that time-resolved Coulomb explosion imaging is sensitive to the localization of charge in extended molecules.

2018-01-09, Young, Linda, Ueda, Kiyoshi, Gühr, Markus, Bucksbaum, Philip H., Simon, Marc, Mukamel, Shaul, Rohringer, Nina, Prince, Kevin C., Masciovecchio, Claudio, Meyer, Michael, Rudenko, Artem, Rolles, Daniel, Bostedt, Christoph, Fuchs, Matthias, Reis, David A., Santra, Robin, Kapteyn, Henry, Murnane, Margaret, Ibrahim, Heide, Légaré, François, Vrakking, Marc, Isinger, Marcus, Kroon, David, Gisselbrecht, Mathieu, L’Huillier, Anne, Wörner, Hans Jakob, Leone, Stephen R.

X-ray free-electron lasers (XFELs) and table-top sources of x-rays based upon high harmonic generation (HHG) have revolutionized the field of ultrafast x-ray atomic and molecular physics, largely due to an explosive growth in capabilities in the past decade. XFELs now provide unprecedented intensity (1020 W cm−2) of x-rays at wavelengths down to ∼1 Ångstrom, and HHG provides unprecedented time resolution (∼50 attoseconds) and a correspondingly large coherent bandwidth at longer wavelengths. For context, timescales can be referenced to the Bohr orbital period in hydrogen atom of 150 attoseconds and the hydrogen-molecule vibrational period of 8 femtoseconds; wavelength scales can be referenced to the chemically significant carbon K-edge at a photon energy of ∼280 eV (44 Ångstroms) and the bond length in methane of ∼1 Ångstrom. With these modern x-ray sources one now has the ability to focus on individual atoms, even when embedded in a complex molecule, and view electronic and nuclear motion on their intrinsic scales (attoseconds and Ångstroms). These sources have enabled coherent diffractive imaging, where one can image non-crystalline objects in three dimensions on ultrafast timescales, potentially with atomic resolution. The unprecedented intensity available with XFELs has opened new fields of multiphoton and nonlinear x-ray physics where behavior of matter under extreme conditions can be explored. The unprecedented time resolution and pulse synchronization provided by HHG sources has kindled fundamental investigations of time delays in photoionization, charge migration in molecules, and dynamics near conical intersections that are foundational to AMO physics and chemistry. This roadmap coincides with the year when three new XFEL facilities, operating at Ångstrom wavelengths, opened for users (European XFEL, Swiss-FEL and PAL-FEL in Korea) almost doubling the present worldwide number of XFELs, and documents the remarkable progress in HHG capabilities since its discovery roughly 30 years ago, showcasing experiments in AMO physics and other applications. Here we capture the perspectives of 17 leading groups and organize the contributions into four categories: ultrafast molecular dynamics, multidimensional x-ray spectroscopies; high-intensity x-ray phenomena; attosecond x-ray science.