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FLASH-News
25-Jul-2023
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Result defies established models of nanoparticle behaviour
Photocatalysis, sensors, solar cells: nanoparticles that are excited by light promise a variety of applications, if the processes behind their behaviour can be controlled. One such process is a type of collective electron motions. These movements lead to energy exchange in the nanoparticle that give them their characteristics but that can also be disruptive. However, so far the exact behaviour of those movements was unclear. A research team comprising scientists from the Center for Free-Electron laser Science (CFEL) at DESY, Universität Hamburg, the Max-Planck-Institute for the Structure and Dynamics of Matter, Hamburg, and TU Berlin reports in the journal Nano Letters experimental observations of a molecular movie recorded at DESY’s FLASH free-electron laser that cannot be explained by established models. In response to these findings, the team has provided a new theoretical model that explains their experimentally observed dynamics of the excited gold nanoparticles. The image Illustrates a gold nanoparticle: the researchers found that when activated by a light pulse, the electrons in the particle already shift, far sooner than earlier believed.
Reference: Time-resolved single-particle X-ray scattering reveals electron-density gradients as coherent plasmonic-nanoparticle-oscillation source; Dominik Hoeing, Robert Salzwedel, Lena Worbs, Yulong Zhuang, Amit K. Samanta, Jannik Lübke, Armando D. Estillore, Karol Dlugolecki, Christopher Passow, Benjamin Erk, Nagitha Ekanayake, Daniel Ramm, Jonathan Correa, Christina C. Papadopoulou, Atia Tul Noor, Florian Schulz, Malte Selig, Andreas Knorr, Kartik Ayyer, Jochen Küpper, Holger Lange; Nano Letters, 2023; DOI:10.1021/acs.nanolett.3c00920
28-Jun-2023
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Ultrashort Pulses at FLASH
Ultrashort soft X-ray pulses generated at FLASH made it to the Photonics Cover Story. The presented concept overcomes the coherence time barrier and results in ultrashort pulses in X-ray Free Electron Lasers. As well as a numerical illustration, the results of the first experimental test at the soft X-ray FEL user facility FLASH are presented in Photonics.
The pulse duration in short-pulse schemes for Self-Amplified Spontaneous Emission Free-Electron Lasers (SASE FELs) is limited by the FEL coherence time. A recently proposed concept allows to overcome the coherence time barrier and to obtain much shorter pulses. When the lasing part of an electron bunch is much shorter than the coherence time, one can suppress the radiation in the long main undulator while preserving microbunching within that short lasing slice. Then, a short radiation pulse is produced in a relatively short radiator. A possible suppression method, an excessive reverse undulator taper, is discussed and illustrated numerically. The first experimental tests of this method is performed at the soft X-ray FEL user facility FLASH. The measured pulse duration approaches 1 fs (FWHM) at the wavelength of 5 nm.
From: Abstracts of the article by E. Schneidmiller Photonics, Volume 10, Issue 6 (June 2023).
The image shows the Photonics cover story: "This concept overcomes the coherence time barrier and results in ultrashort pulses in X-ray Free Electron Lasers. As well as a numerical illustration, the results of the first experimental test at the soft X-ray FEL user facility FLASH are presented. The measured pulse duration approaches 1 fs (FWHM) with pulse energies of 1.5 µJ at a wavelength of 5 nm. The application of the proposed technique to hard X-ray FELs can open the way to generate extremely short pulses, in the range of a few tens of attoseconds."
Reference: Schneidmiller, E.; Dreimann, M.; Kuhlmann, M.; Rönsch-Schulenburg, J.; Zacharias, H. Generation of Ultrashort Pulses in XUV and X-ray FELs via an Excessive Reverse Undulator Taper. Photonics 2023, 10, 653. DOI:10.3390/photonics10060653
20-Mar-2023
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A critical milestone towards FLASH2020+ achieved
External seeding via Echo-Enabled Harmonic Generation (EEHG) has been established for the first time at FLASH. This is a major step towards FLASH2020+ external seeding, achieved by a major effort of the Xseed team with the support of many FLASH experts. Compared to standard SASE operation, the spectral quality and the longitudinal coherence are drastically improved and will ultimately allow for the next generation of user experiments.
The image shows a couple of plots related to the experiment. The graphs on the left-hand side illustrates the spectral properties of EEHG and HGHG at 22.1 nm, the 12th harmonic of the seed lasers fundamental of 266 nm. Evident are for example the reduced spectral bandwidth (left bottom) and high spectral reproducibility (left centre). Also the plots on the right-hand side demonstrate that upon variation of the strength of the second (bunching) chicane EEHG has an increased wavelength stability (right centre) and rather broad peak ins spectral intensity (right top). In addition the transverse mode of FLASH2 lasing in SASE mode is shown in the bottom centre.
EEHG is a seeding technique based on the interaction of the electron beam with two lasers to generate fully coherent and stable FEL pulses at harmonic wavelengths of the 266 nm seed laser (tripled Ti:Sa). In our case, we explored the 9th (29.5 nm), 12th (22.1 nm), 15th (17.7 nm), and 17th (15.6 nm) harmonics. A few selected results taken with the 12th harmonic at 22.1 nm are shown in the image. Here the difference between EEHG and the two operation modes High-Gain Harmonic Generation, overlapping a seed laser with the electron beam in just a single stage, are especially highlighted. While both seeded operation modes provide clean and reproducible spectra in contrast to SASE, the benefit of smallest spectral bandwidth and highest spectral intensity for EEHG is evident.
A week after the first demonstration the Xseed team was able to timely re-establish EEHG seeding conditions after accelerator maintenance in 4 hours. Among others, this time two electron bunches were distributed to the FLASH1 beamline - mimicking the shortest possible bunch-train. Upon shifting of the seed laser timing the output radiation properties in the two cases could be compared. This is a critical point towards FL2020+, where we plan to seed bunch trains up to 500 bunches at MHz repetition rate.
In parallel to seeding operation, the FLASH2 beamline was operated in SASE at 30 nm with intensities above 100 uJ and a nice transverse mode. This is another "first" worldwide and a crucial milestone as it demonstrates the feasibility of the future FLASH operation concept.
We would like to thank everyone involved.
10-Feb-2023
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Reaction of high interest to clean-energy innovations is closely analysed in X-ray study
Experiments at DESY’s light sources PETRA III and FLASH have revealed the complex mode of action behind the artificial splitting of water at its most efficient level. Using X-rays, a team led by DESY leading scientist Simone Techert managed to observe the interaction of water with a perovskite, a class of mineral that is of interest in many new materials and that is well-known as a catalyst for the breaking apart of water molecules into constituent hydrogen and oxygen molecules. This observation and analysis can help further improve the process, which can be used for efficient and clean production of so-called “green” hydrogen and oxygen for fuel cells and improved battery technologies, among other potential uses, such as in the chemical industry. The research has been published in the journal Accounts of Chemical Research.
The image shows a general overview of the neural network (β-VAE-network): from raw data to reconstruction. (Image from authors: HZB)
Reference: Torben Reuss, Sreeju Sreekantan Nair Lalithambika, Christian David, Florian Döring, Christian Jooss, Marcel Risch, and Simone Techert; Advancements in Liquid Jet Technology and X-ray Spectroscopy for Understanding Energy Conversion Materials during Operation; Accounts of Chemical Research, 2023;DOI: 10.1021/acs.accounts.2c00525
6-Jan-2023
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Successfully used in photon diagnostics at FLASH
Experimental data is often not only highly dimensional but also noisy and full of artefacts which makes it difficult to interpret them. Now a team from Helmholtz-Zentrum Berlin (HZB), together with scientists from DESY, University of Potsdam and University of Kassel, has designed software and tested it at FLASH. This software uses self-learning neural networks to compress the data in a smart way and reconstruct a low-noise version in the next step. It enables to recognise correlations that would otherwise not be discernible and has been successfully used in photon diagnostics experiments at FLASH at DESY.
In the published study, the team used the software to determine the photon energy of FLASH from single-shot photoelectron spectra. They succeeded in extracting this information from noisy electron time-of-flight data and much better than with conventional analysis methods. Even data with detector-specific artefacts can be 'cleaned up' this way.
The image shows a general overview of the neural network (β-VAE-network): from raw data to reconstruction. (Image from authors: HZB)
Reference: Gregor Hartmann, Gesa Goetzke, Stefan Düsterer, Peter Feuer-Forson, Fabiano Lever, David Meier, Felix Möller, Luis Vera Ramirez, Markus Gühr, Kai Tiedtke, Jens Viefhaus and Markus Braune, "Unsupervised realworld knowledge extraction via disentangled variational autoencoders for photon diagnostics", Sci Rep 12, 20783 (2022),DOI: 10.1038/s41598-022-25249-4
21-Dec-2022
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A new study on chiral molecules
In a recent study, researchers at Freie Universität Berlin, DESY, Kiel University, and Kansas State University have shown how light can turn a planar molecule into a chiral molecule with just one particular handedness, With the theoretical study which was published in the internationally renowned scientific journal Science Advances in December, the team provides a solution to the long-standing problem of absolute asymmetric synthesis.This new process could be particularly useful in chemically synthesizing compounds.
The authors argue that the proposed experiment is feasible with already existing setups, for example, by means of the circular polarization provided by FLASH at DESY. The image gives an impression how chiral molecules exist in two mirror-image forms, similar to the left and right hand. (Image: Denis Tikhonov)
The study was carried out as part of the Collaborative Research Centre 1319 “Extreme Light for Sensing and Driving Molecular Chirality” (ELCH).
Reference: Denis S. Tikhonov, Alexander Blech, Monika Leibscher, Loren Greenman, Melanie Schnell, and Christiane P. Koch. “Pump-probe spectroscopy of chiral vibrational dynamics”, Science Advances, Vol 8, Issue 49 (2022), eade0311; DOI:10.1126/sciadv.ade0311
9-Nov-2022
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Resonant two-photon ionisation of helium measured with angular resolution
Using a new experimental method, physicists from the Max Planck Institute for Nuclear Physics in Heidelberg investigated the resonant two-photon ionisation of helium with improved spectral resolution and angular resolution. For this purpose, they utilised a reaction microscope in combination with a high-resolution extreme-ultraviolet (EUV) photon spectrometer developed at the Institute. The measurements have been performed at the Free Electron Laser in Hamburg (FLASH), a brilliant radiation source, delivering intense EUV laser flashes. This allows the events from each individual laser flash to be analysed in terms of photon energy, yielding spectrally high-resolution data sets. The image shows the spectrum of photons unsorted (top) and sorted by peak position (bottom). (Image: MPIK)
Reference: M. Straub et al.: Differential Measurement of Electron Ejection after Two-Photon Two-Electron Excitation of Helium, Phys. Rev. Lett. 129, 183204 (2022); DOI:10.1103/PhysRevLett.129.183204
1-Oct-2022
23-Aug-2022
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DESY's free-electron laser FLASH shows chemical changes in surfaces
Consider the humble plastic food wrapper. It may seem like a simple clear film that wraps a loaf of bread or fruit gummies, but these films are less simply composed as it seems. Each individual layer must be chemically treated so that it adheres well to the next. In their efforts to adapt an established X-ray analysis method to X-ray lasers, DESY scientists in collaboration with researchers at the Leibniz Institute for Plasma Science and Technology in Greifswald, Germany, have ended up showing potential improvements in the preparation of such plastic films made of polyethylene terephthalate (PET). DESY researcher Elke Plönjes lead a team that examined the surfaces of the layers at FLASH using a technique known as X-ray ptychography.
“With X-ray ptychography, we were able to image the three-dimensional structure of the PET surface in a larger area with a resolution similar to electron microscopy,” says Plönjes. “Even in these very smooth samples with only minor changes on the surface, we were able to visualize them and study the surface quality in detail.”
The image shows an example that film packaging for medicines (blisters) are often made of PET plastic. Credit: Pixabay
Reference: X-ray Ptychographic Imaging and Spectroscopic Studies of Plasma-Treated Plastic Films; Mehdi Ravandeh, Masoud Mehrjoo, Konstantin Kharitonov, Jan Schäfer, Antje Quade, Bruno Honnorat, Mabel Ruiz-Lopez, Barbara Keitel, Svea Kreis, Rui Pan, Seung-gi Gang, Kristian Wende, and Elke Plönjes; Polymers, 2022; DOI: 10.3390/polym14132528
15-Aug-2022 / 22-Sep-2022
1-Jun-2022
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Scientists watch moving charge density in real-time
An international research team led by DESY scientist Tim Laarmann has for the first time been able to monitor the quantum mechanically evolving electron charge distribution in glycine molecules via direct real-time measurement. The results – obtained at DESY´s brilliant free-electron laser FLASH – are published in the scientific journal Science Advances. Better knowledge of the quantum effects in the motion of electrons at the molecular level can pave the way to controlling, optimising, and engineering ionising radiation to be used for example in radiotherapy for cancer treatment.
The image shows that in the pump-probe experiment the glycine molecule is first ionised by the high intensity X-ray pulse from DESY's free-electron laser FLASH (left). This induces a correlated motion of the valence electrons and holes, depicted by red and blue lobes. After a variable time delay from 0 to 175 femtoseconds the probe pulse samples the state of the glycine ion and electron motion through further ionisation and measurement of the ionisation products (right). In this example, a time delay of 10 femtoseconds is depicted, which shows two extrema of the oscillatory electron/hole motion, i.e. a half period of the electron coherence. Credit: DESY, David Schwickert
Reference: Electronic quantum coherence in glycine molecules probed with ultrashort x-ray pulses in real time; David Schwickert, Marco Ruberti, Přemysl Kolorenč, Sergey Usenko, Andreas Przystawik, Karolin Baev, Ivan Baev, Markus Braune, Lars Bocklage, Marie Kristin Czwalinna, Sascha Deinert, Stefan Düsterer, Andreas Hans, Gregor Hartmann, Christian Haunhorst, Marion Kuhlmann, Steffen Palutke, Ralf Röhlsberger, Juliane Rönsch-Schulenburg, Philipp Schmidt, Sven Toleikis, Jens Viefhaus, Michael Martins, André Knie, Detlef Kip, Vitali Averbukh, Jon P. Marangos, Tim Laarmann;
Science Advances, 8, eabn6848 (2022); DOI: 10.1126/sciadv.abn6848
19-May-2022
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Resonant four-wave mixing spectroscopy at FLASH
A team of researchers from Max Born Institute (MBI) in Berlin, and DESY has now observed a new kind of such wave mixing process involving soft X-rays at FLASH. Overlapping ultrashort pulses of soft X-rays and infrared radiation in a single crystal of lithium fluoride (LiF), they see how energy from two infrared photons is transferred to or from the X-ray photon, changing the X-ray “color” in a so-called third-order nonlinear process. Not only do they observe this particular process with X-rays for the first time, they were also able to map out its efficiency when changing the color of the incoming X-rays. It turns out that the mixing signals are only detectable when the process involves an inner-shell electron from a lithium atom being promoted into a state where this electron is tightly bound to the vacancy it left behind – a state known as exciton. Furthermore, comparison with theory shows that an otherwise “optically forbidden” transition of an inner-shell electron contributes to the wave mixing process.
The image shows two light beams from flashlights will not be influenced by each other when they cross. This is different for very intense laser pulses which meet in a suitable “nonlinear material” – here, beams can be deflected and new beams of different color can be created in a process called wave-mixing. The observation of such wave-mixing phenomena allows researchers to draw conclusions about electronic transitions within the nonlinear material which are otherwise invisible. Researchers from MBI and DESY have now observed how an X-ray beam interacts with a laser beam, paving a route to atom-selective studies of ultrafast processes in the future. (Image credit: Anne Riemann, Forschungsverbund Berlin e.V.)
Reference: Probing electron and hole colocalization by resonant four-wave mixing spectroscopy in the extreme ultraviolet, Horst Rottke, Robin Y. Engel, Daniel Schick, Jan O. Schunck, Piter S. Miedema, Martin C. Borchert, Marion Kuhlmann, Nagitha Ekanayake, Siarhei Dziarzhytski, Günter Brenner, Ulrich Eichmann, Clemens von Korff Schmising, Martin Beye, Stefan Eisebitt, Science Advances (2022). DOI: 10.1126/sciadv.abn5127
18-May-2022
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Study shows ultrafast dynamics of electron orbitals in molecules
Researchers from Universität Hamburg, European XFEL and DESY have succeeded in looking at details of molecular orbitals at DESY's free-electron laser FLASH. The team reports in the journal Nature Communications on the new method, which makes it possible to observe the temporal change of the wave function of molecules. These changes are crucial for reactions of molecules on surfaces and can lead to new insights into the development of functional devices.
The image shows a snapshots of molecular orbitals contain high-precision details about photoinduced electronic and nuclear transformations on sub-picosecond time scales. Credit: Universität Hamburg, Marvin Reuner und Daria Gorelova
Reference: Ultrafast orbital tomography of a pentacene film using time-resolved momentum microscopy at a FEL; Kiana Baumgärtner, Marvin Reuner, Christian Metzger, Dmytro Kutnyakhov, Michael Heber, Federico Pressacco, Chul-Hee Min, Thiago Peixoto, Mario Reiser, Chan Kim, Wei Lu, Roman Shayduk, Manuel Izquierdo, Günter Brenner, Friedrich Roth, Achim Schoell, Serguei Molodtsov, Wilfried Wurth, Friedrich Reinert, Anders Madsen, Daria Popova-Gorelova, and Markus Scholz; Nature Communications, 2022; DOI: 10.1038/s41467-022-30404-6
22-Mar-2022
03-Mar-2022
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New experimental finding reveals the potential of plasma as energy booster for high-rate accelerators
An international team of researchers led by DESY scientists has demonstrated for the first time at the FLASHForward experiment that in principle it is possible to operate plasma accelerators at the repetition rates desired by particle physicists and photon scientists. This opens the opportunity to utilise such high-gradient accelerators as booster stages in existing high-repetition-rate facilities, such as the large-scale X-ray free-electron lasers FLASH and European XFEL, in order to significantly increase the energy of long trains of particles in short distances. The team presents the results of their studies in the journal Nature.
The image shows the two FLASHForward plasma cells observed through a vacuum window. The cells are filled with argon gas and then ionised with a high-voltage electrical discharge to form a plasma. As the plasma recombines it emits light in the blue wavelength range. Both plasma cells, of length 50 and 195 millimetres, can then be used for plasma acceleration of electron bunches in gigavolt-per-metre accelerating gradients. Photo: DESY, C.A. Lindstrøm
Reference: Recovery time of a plasma-wakefield accelerator; R. D’Arcy, J. Chappell, J. Beinortaite, S. Diederichs, G. Boyle, B. Foster, M.J. Garland, P. Gonzalez Caminal, C.A. Lindstrøm, G. Loisch, S. Schreiber, S. Schröder, R.J. Shalloo, M. Thévenet, S. Wesch, M. Wing, and J. Osterhoff; Nature 603, 34-35 (2022), DOI:10.1038/d41586-022-00544-2 and Nature "News and Views" 02 March 2022 DOI:10.1038/s41586-021-04348-8
2-Mar-2022
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Recovery time of a plasma-wakefield accelerator
"Particle accelerators are usually associated with the discovery of fundamental particles, but they also have a long history of powering light sources. One such source is the free-electron laser, in which a high-energy beam of electrons from a linear accelerator generates ultrashort X-ray laser pulses by travelling through a series of magnets. However, conventional accelerators are expensive and unwieldy, needing up to one kilometre of space under Earth’s surface, and a smaller, cheaper accelerator based on plasma (ionized gas) might be capable of doing the job. The plasma in such a device needs to settle before each new interaction with the electron beam, but the interactions must be repeated at a high rate to power a free-electron laser that has sufficient average brilliance. Writing in Nature, D’Arcy et al. report that the maximum repetition rate of a plasma-based accelerator could be as high as one million times per second — or even higher, putting it comfortably in the realm of nearly all potential applications."
Extraction of the article by Michel Litos Nature News and Views, 02 March 2022.
The image illustrates that for the perturbed measurements, a leading bunch drives a wakefield, which in turn stimulates motion of the plasma ions. The two probe bunches sample the perturbed plasma in increments of 0.77 ns after the temporally locked leading bunch. For the unperturbed measurements, the procedure is the same but without the presence of the leading bunch. The rendering was performed using VisualPIC33.
The experiment was taken out at FLASHForward, the third beamline of the free-electron laser facility FLASH.
Reference: R. D’Arcy, J. Chappell, J. Beinortaite, S. Diederichs, G. Boyle, B. Foster, M. J. Garland, P. Gonzalez Caminal, C. A. Lindstrøm, G. Loisch, S. Schreiber, S. Schröder, R. J. Shalloo, M. Thévenet, S. Wesch, M. Wing & J. Osterhoff, "Recovery time of a plasma-wakefield accelerator", Nature 603, 58–62 (2022); DOI:10.1038/s41586-021-04348-8
24-Feb-2022
24-Jan-2022
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Investigating the harsh environment of interstellar space in a FLASH
Using DESY's free-electron laser FLASH, scientists have recreated some of the harsh environment of interstellar space in the lab and analysed the reaction of astrochemical molecules to these conditions. The results show a comprehensive picture of the dynamics of polycyclic aromatic hydrocarbons (PAH) under extreme ultraviolet radiation in a vacuum – resembling the cosmic environment between the stars of our galaxy, the Milky Way. As the international team led by DESY scientists Bastian Manschwetus and Melanie Schnell write, the results promote understanding of organic chemistry in space. Their study has been published in the journal Nature Communications, and is featured in DESY's new Photon Science 2021 highlights report.
The image shows polycyclic aromatic hydrocarbons (PAHs) which are compounds consisting of carbon rings (black) with various numbers of hydrogen atoms (grey) attached. Infrared observations show these molecules are ubiquitous in space. Credit: DESY, Bastian Manschwetus (Background NASA/Hubble).
Reference:
Time-Resolved Relaxation and Fragmentation of Polycyclic Aromatic Hydrocarbons Investigated in the Ultrafast XUV-IR Regime; J. W. L. Lee, D. S. Tikhonov, et al.; Nature Communications, 2021; DOI: 10.1038/s41467-021-26193-z
18-Jan-2022
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Investigating the specific timescale of spin and electron dynamics
Spintronics, the manipulation of electron spins and magnetic moments, is aimed at supplying an alternative to conventional electronics technology which uses the change of electronic states to store and transfer information using binary bits. At FLASH, an international research team, including the Central European Institute of Technology (CEITEC) in Brno (Czech Republic) and the University of Mainz, has now addressed the problem of ultrafast generation of magnetic ordering in a possible candidate for the realisation of spintronic devices. To solve this question, they combined time-resolved soft X-ray photoemission with state-of-the-art time-dependent Density Functional Theory (DFT) calculations.
The image shows the FeRh structure and magnetic moments in the anti-ferromagnetic phase (partly from original publication).
Reference:
F. Pressacco, et al., Subpicosecond metamagnetic phase transition in FeRh driven by non-equilibrium electron dynamics, Nat. Commun. (2021), DOI: 10.1038/s41467-021-25347-3
13-Jan-2022
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An international research team led by Markus Gühr’s group at the University of Potsdam performed laser experiments at DESY's free-electron laser FLASH to monitor charge motions in light-excited molecules of thiouracil, which is a modified nucleobase. This class of molecules has a variety of medical applications, including possible novel cancer therapies. Their basic research now published in Nature Communications opens up the possibility to map the charge flowing inside the molecular landscape.
The image shows the charge density induced by ultraviolet excitation (red means less electrons, blue means more) in the molecule 2-thiouracil. The X on the structure marks the sulfur atom, where the authors investigated the charge flow using time resolved x-ray photoelectron spectroscopy. The molecule jumps for the first few 100 femtoseconds between the two electron configurations indicated. Image Credit: University of Potsdam, David Picconi/Markus Gühr [Source]
Reference: Following excited-state chemical shifts in molecular ultrafast x-ray photoelectron spectroscopy; Mayer, D., Lever, F., Picconi, D. et al.; Nature Communications, 2022; DOI: 10.1038/s41467-021-27908-y
16-Nov-2021
29-Jul-2021
21-Jul-2021
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Microscopic imaging using X-ray free-electron lasers like FLASH enables studies of structural features with a resolution down to a few nanometers and has become a major field of these facilities worldwide.
Ptychography, as a modern computational microscopy technique, simultaneously retrieves the object under study and information on the light pulses illuminating it. High-resolution ptychographic images are collected through scanning a larger object by the focused free-electron lasers (FEL) pulses. It has to be ensured that the light pulses are moved across the sample with sufficient overlap from position to position. This process allows the retrieval of both, object and light pulse. However, standard ptychography algorithms require an ideal stable light pulse from shot to shot. Thus, the chaotic fluctuations of the FEL pulse properties, caused by the SASE (self-amplified spontaneous emission) process, complicate the implementation and data analysis of such experiments under real conditions.
To overcome these difficulties and to facilitate ptychography at FELs, a research team from FLASH at DESY developed a new computational framework.
The image shows a reconstructed sample through the A-AD ptychography at the FLASH2 facility at the beamline FL24. Without applying the A-AD model it was impossible to fully retrieve the sample. The A-AD concept relaxes the constraints and disentangles the uncertainties (Figure from original publication).
DOI:10.1364/OE.426931
08-Jul-2021
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A large international collaboration of scientists from the Max-Planck Institute for Nuclear Physics (MPIK) in Heidelberg, DESY, Heidelberg University, University of Münster and many others demonstrated for the first time an all-XUV (extreme ultraviolet) time-resolved absorption spectroscopy investigation of a small molecule: the photoinduced structural dynamics of diiodomethane. By means of the short wavelength of XUV laser pulses, individual atoms in the molecule can be addressed specifically via a well-defined electronic excitation.
The team, headed by Christian Ott from the division of Thomas Pfeifer at the MPIK, performed the experiment at the FLASH beamline BL2 at DESY. Two identical XUV pulses with a variable time delay interact subsequently with an iodine atom of CH2I2. The excitation during the first pulse triggers the dissociation of the molecule, which includes a structural deformation through a short-lived isomeric state (see sketches ①②③ in the figure).
Image: Sketch of the all-XUV pump-probe time-resolved measurement of the molecular structural dynamics of the diiodomethane molecule at FLASH (Figure: © MPIK Heidelberg).
DOI:10.1103/PhysRevX.11.031001
22-Apr-2021
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Scientists used terahertz radiation for measurements of strongly excited material
In-depth understanding of the electrical conductivity of matter is the key to many cutting-edge research and applications, ranging from phase-change memory in microelectronics to magnetospheres rooted in planetary interiors due to the motion of the conductive fluid. Unique states of material created by ultrafast table-top lasers or free-electron lasers (FEL) allow us to gain insight into atomic levels. However, it also requires sub-picosecond resolution to capture the details on the timescale of atomic motion.
An international research team, led by scientists from the SLAC National Accelerator Laboratory and DESY, have recently measured the electrical conductivity of strongly heated material using the THz FEL radiation at FLASH. In this study, gold nano-foil samples were heated by the FLASH extreme ultraviolet (XUV) FEL pulses to electron temperatures up to 16,000 °C. As the thermal energy transfers from the electrons to the ions, the sample transits from cold to superheated solid and eventually melts into warm dense liquid. The researchers have determined the DC electrical conductivity by measuring the transmitted THz electric field through the heated samples. The multi-cycle THz pulses from FLASH provide continuous measurements with temporal resolutions better than 500 femtoseconds.
Image: The FLASH XUV pulse heats the gold nanofoil samples to electron temperature above 16,000 °C while the multi-cycle THz pulse enables measuring the electrical conductivity of the nanofoil samples as thermal energy transfers from electrons to ions (Credit: Z. Chen, SLAC).
DOI:10.1038/s41467-021-21756-6
24-Feb-2021
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Study at FLASH with femtosecond time-resolved X-ray photoemission spectroscopy (TR-XPS)
Molecular heterojunctions receive significant attention due to their key role in a wide variety of emerging organic semiconductor applications, such as organic light-emitting diodes, field-effect transistors, spintronic devices, and photovoltaic cells. Understanding ultrafast dynamics of photon-to-charge conversion is paramount for optimising novel light-harvesting systems. By using the femtosecond long X-ray pulses of the free-electron laser FLASH at the plane-grating monochromator beamline PG2 and the wide-angle electron spectrometer (WESPE) end station, the team of researchers has access to specific charge separation sites and monitor free charge formation in a model donor-acceptor system on their natural timescale.
Image: Left: 2D false-colour map of the measured time-dependent C 1s signal of the CuPc:C60 heterojunction as a function of time-delay and kinetic energy and schematic representation of the time-resolved XPS experiment and the observed kinetics. (Figures from original publication F. Roth et al., licensed under a Creative Commons Attribution 4.0)
DOI:10.1038/s41467-021-21454-3
25-Nov-2020
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New method displays accelerating field in plasma accelerator with unparalleled precision
The technology of plasma-based acceleration promises to deliver a new generation of powerful and compact particle accelerators. Prior to applying this new technology, however, various obstacles must be overcome. In particular precise control of the acceleration process itself must be achieved. Using an innovative technique researchers at DESY have now succeeded in measuring the accelerating plasma wake with previously unattained precision. Their method allows the shape of the effective accelerating field to be determined with a resolution on the order of femtoseconds (trillionths of a millionth of a second) so that the acceleration process can be studied in great detail, thereby paving the way for the controlled and optimised operation of future plasma accelerators, as the team led by DESY’s Jens Osterhoff explains in the journal Nature Communications.
Image: View of the FLASHForward accelerator module. The plasma is generated in the narrow channel in the centre by a high voltage. Credit: DESY, Alexander Knetsch
DOI:10.1038/s41467-020-19811-9
24-Nov-2020
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Free electron laser study sheds light on the mechanism and timescale of the photocatalytic oxidation of carbon monoxide on titanium oxide
An international team of scientists have studied, for the first time, the light induced oxidation of carbon monoxide (CO) to carbon dioxide (CO2) on the surface of an oxide photocatalyst in real-time using the soft X-ray free-electron laser FLASH combined with theoretical calculations. According to their findings, which are published in the journal ACS Catalysis, the photoconversion of CO to CO2 takes place between 1.2 and 2.8 picoseconds (ps) after the reaction is triggered by an ultrafast optical laser pulse.
Image: Using FLASH, the research team was able to precisely resolve that between 1.2 and 2.8 picoseconds after triggering, the carbon monoxide oxidised to carbon dioxide.
DOI:10.1021/acscatal.0c04098
11-Aug-2020
FLASH2020+ Kick-Off Meeting 3-Jul-2020
Impression from the virtual Kick-off meeting of the FLASH2020+ project at DESY on 3 July 2020, including images of the speakers (Credit: DESY).
FLASH2020+ technical design phase started
Making FLASH brighter, faster and more flexible
The technical design phase of the FLASH2020+ project at DESY started with an internal virtual kick-off meeting. Over 270 participants mainly from DESY and the campus in Hamburg joined the project team online on 3 July 2020. Key topics were the upgrade project of the free-electron laser (FEL), scientific goals, the embedding at DESY and the international landscape, the project structure and its timeline over the next five years.
The FLASH2020+ project is based on the long history of FLASH at DESY, from its inception as a test facility for the TESLA project in the mid-90s of the last century to the worldwide first XUV to soft X-ray FEL user facility ten years later. With the FLASH2 project, it is now the first FEL that runs two independent undulator lines in parallel, again about ten years later.
In 2020, yet another ten years later, the project is right in time to make the next step forward with the facility where especially the external seeding and shorter pulses will enable new and unique scientific opportunities. The upgrade will keep FLASH at the forefront of science with FELs for the next decade, as highlighted by Edgar Weckert, director in charge for DESY Photon Science. The importance of the project for the DESY strategy to further advance DESY’s machines and to develop new technologies for future accelerators was stressed by Wim Leemans, the DESY director of the accelerator division. With such a project, DESY contributes also to the technical developments in FEL science and teaching of the next generation of scientists.
The FLASH2020+ project is be led by Enrico Allaria, who presented the project phases, timeline and structure. He is an expert from the FEL “FERMI” in Trieste (Italy) and has just started to work at DESY.
Further information (slides) from the FLASH2020+ kick-off meeting web pages.
FLASH2020+: millions for the modernisation towards ultrashort snapshots (904KB)
Press and Public Relations - FLASH2020+
DESY Press and Public Relations - Mai 2020
6-Apr-2020
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4-Sep-2015
Kai and Albert
Kai Siegbahn was awarded the 1981 Nobel Prize in physics for “his contribution to the development of high-resolution electron spectroscopy”.
Albert Einstein received the 1921 Nobel Prize in physics for “his services to theoretical physics, and especially for his discovery of the law of the photoelectric effect”.
20-May-2015
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14-Jan-2015
10 years of SASE at FLASH
Back in 2005, early in the morning of January 14th, first SASE has been observed at DESY's newly installed VUV free-electron laser. The electron beam has been accelerated to 445 MeV corresponding to a wavelength of 32 nm. In summer 2005, the VUV-FEL turned into a user facility named FLASH.
The image shows the Spectrum of the first SASE signal measured in the early morning of January 14th, 2005.
20-Aug-2014
SASE FEL radiation observed on a Ce:YAG screen of the FLASH2 photon beamline.
20-Aug-2014
5-Aug-2014
21-Jul-2014
12-May-2014
11-Mar-2014
24-Feb-2014
Fifth user period started 24-Feb-2014 with its first beam time block
Coming out of a long shutdown to finish up the construction of the new beamline FLASH2, the fifth user period for beamline FLASH1 has started end of February with its first user block. Until April 2015, more than 5000 hours of user experiments are scheduled. Beam time will also be available for accelerator and photon beam line studies as well as for FLASH2 commissioning. FLASH2 saw first beam in March 2014 pushing the beam to the dump for the first time May, 23. Since then, FLASH2 is operated in parallel to FLASH1 whenever possible to finish up the commissioning of beam diagnostics and to refine beam optics. First SASE radiation at 40 nm has been seen on Aug 20, 2014. The next goal is to characterize the SASE radiation, to measure gain length for example for as many other wavelength.
The image shows a schematic layout of FLASH. Not to scale. The second beamline, FLASH2, is being commissioned.
25-Sep-2013
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26-Jul-2013
Installation of the new switch yard and extraction beamline to FLASH2 ready to go. The extraction beamline turns to the right through the new opening of the FLASH tunnel towards the FLASH2 beamline hall.
18-Nov-2012
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