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24-Jan-2022

Cosmic chemistry in the lab

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

Sub-picosecond metamagnetic phase transition in FeRh

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

Watching the charge move in photoexcited molecules

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

FLASH is in a Shutdown Period for Major Upgrades
16-November-2021 to 14-August-2022

Key items:
- Energy Upgrade
- Cryogenics
- Injector upgrade
- FLASH2 Afterburner
- FLASHForward
- XSEED

29-Jul-2021

FLASH2020+: Lucas Schaper Takes Over as Head of the Project

The FLASH2020+ project is DESY’s latest upgrade for the free-electron laser FLASH. Many technological improvements will increase the flexibility of the machine and enable the production of even brighter light in the future for the users. Since July 2020, the project has been led by seeding expert Enrico Allaria. On September 2021, he handed over the management of the ambitious project to DESY colleague Lucas Schaper, who has worked shoulder to shoulder with Enrico since the start of the project.

The image shows Lucas Schaper (left) takeing over the management of the FLASH2020+ project from Enrico Allaria (right).[Photo: DESY/M. Mayer]

21-Jul-2021

Novel computational framework streamlines ptychography imaging at FLASH

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

Timing molecular structural dynamics both excited and probed by extreme ultraviolet light

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

Microscopic origins of electrical conductivity in superheated solids revealed at FLASH

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

Direct observation of charge separation in an organic light-harvesting system

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

Measuring the Wave

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

FLASH reveals ultrafast dynamics of photocatalysis

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

XUV lasing from exploding noble-gas nanoclusters

New mechanism of XUV light amplification

An international team of scientists, headed by Nina Rohringer from DESY and Unversität Hamburg, has succeeded in getting bursts of laser-like extreme ultraviolet (XUV) emission from noble-gas clusters in the transient warm dense matter state. Xenon clusters were irradiated by DESY’s free-electron laser FLASH, and the resulting strongly amplified fluorescence signal was analysed by a high-resolution spectrometer. Theoretical modeling of the process indicates that the clusters, transformed to a nanometer-sized plasma (‘nanoplasma’), enable the creation of population inversion by means of electron-ion collisions. The transient but sizeable population inversion of the ensemble of clusters enables amplification of spontaneous emission in a single pass of the emitted XUV radiation. This study, performed at the CAMP station of the FLASH beamline BL1 at DESY, is published in Physical Review A and is highlighted as an Editors’ Suggestion.

The image shows an artist view of excited noble-gas clusters stimulating lasing emission in the forward direction. (Credit: Original publication in Phys. Rev. A (2020) https://doi.org/10.1103/PhysRevA.101.063412)

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.

Indico page FLASH2020+ Kick-Off Meeting

inform. Summer 2020

Newsletter of the DESY research center.

FLASH2020+: millions for the modernisation towards ultrashort snapshots

PR | Press and Public Relations

FLASH2020+: millions for the modernisation towards ultrashort snapshots (904KB)

Press and Public Relations - FLASH2020+

DESY Press and Public Relations - Mai 2020

6-Apr-2020

HEXTOF at FLASH

Merging time-resolved photoemission techniques into a new instrument

In the quest to gain predictive understanding of the functionality of condensed matter systems, the energy and momentum analysis of photoemitted electrons provide the most direct insights. Time-resolved photoemission in combination with the high-repetition rate of the free-electron laser FLASH at DESY enables now to probe the sub-picosecond dynamics of systems at the new versatile instrument for high energy X-ray time-of-flight (HEXTOF) measurements. In particular low-dimensional materials, molecular crystals, and quantum materials can be investigated.

HEXTOF is routinely used at the PG2 beamline at FLASH for pump probe photoemission studies, as well as - in between FLASH beamtimes - with a table-top high harmonic laser source in the Center for Free-Electron Laser Science (CFEL) to perform either sample pre-characterisation before FLASH beamtimes or independent research activities.

Image: 3D model of the HEXTOF setup (Credits: H. Meyer, S. Gieschen (Univ. Hamburg) and D. Kutnyakhov (DESY))

13-Nov-2019

Study at FLASH - Polarization-sensitive reconstruction of THz fields at dielectric interfaces

THz/X-ray pump-probe experiment at DESY

The FLASH THz facility is worldwide leading in providing tunable narrowband Terahertz (THz) pulses with an intrinsic synchronization to soft X-ray pulses. These THz pulses are continuously tunable in the range of 10‐300 μm (4-125 meV) and the energy per pulse is in the range of several 100 μJ for pump-probe experiments at the free-electron laser FLASH at DESY.

A group of scientists from University of Zurich, ETH Zurich, Paul Scherrer Institute (all from Switzerland), Universität Augsburg and DESY utilized this unique high-field THz accelerator-based radiation source to characterize the electric field of the THz pulse, that was driving ultrafast processes at the solid state interfaces. This novel, in-situ approach was using photon streaking. This means that after the soft X-ray pulses from FLASH photoionized the sample the energy and the momentum of the instantaneously created electrons was influenced by the presence of strong THz field, which could be measured.

The image shows THz streaking of the Pt(111) valence level of the thin-film sample. A whole delay trace is shown. (Source: Original publication Optica 2019)

21-Aug-2019

Superfluorescent emission in the UV range

Free-electron laser FLASH coaxes superfluorescent emission from the noble gas xenon

Scientists have for the first time induced superfluorescence in the extreme ultraviolet range. Superfluorescence, or superradiance, could be used to build a laser that does not require an optical resonator. The team headed by DESY’s lead scientist Nina Rohringer used DESY’s free-electron laser FLASH to stimulate xenon, a noble gas, inside a narrow tube, causing it to emit coherent radiation, like a laser. The research team is now presenting its work in the journal Physical Review Letters.

“The phenomenon of superfluorescence was first discovered in the microwave range in the 1970s, and then demonstrated for infrared and optical wavelengths too,” explains Rohringer. “In the meantime, superfluorescence has also been observed in the X-ray domain, and at one time this mechanism was believed to be a promising candidate for building X-ray lasers. Until now, however, superfluorescence had not been demonstrated in the extreme ultraviolet, or XUV, range.”

The image shows the xenon superradiation as a bright line (yellow) in front of the spectrum of a single flash of the free-electron laser. (Credit: Laurent Mercadier, European XFEL)

9-May-2019

DESY mourns the loss of Wilfried Wurth

Leading scientist of FLASH deceased unexpectedly

DESY mourns the loss of one of its pioneers in research at free-electron lasers: Prof. Wilfried Wurth, leading scientist of the free-electron laser FLASH and lead scientist at DESY, died suddenly and unexpectedly.

Wilfried Wurth’s sudden death hit us all very hard. We are losing an excellent scientist and a very esteemed and popular colleague,” says Helmut Dosch, Chairman of the DESY Board of Directors. “We will very much miss his positive nature and his always sharp analysis. Our deepest sympathy and our thoughts are with Wilfried Wurth´s family.”

Wilfried Wurth was lead scientist at DESY and professor of experimental physics at the University of Hamburg. He made a name for himself as an expert in X-ray spectroscopy and the investigation of ultrafast processes such as the observation of chemical reactions on surfaces in real time. Already before he joined DESY in 2014, he was one of the leading researchers at FLASH. He led the Advanced Study Group of the University of Hamburg at the Center for Free-Electron Laser Science, the cooperation of DESY, the Max Planck Society and the University of Hamburg. Wilfried Wurth played an important role in the construction of the center, as well as in the overall cooperation between the University of Hamburg and DESY.

From 2007 to 2013, Wilfried Wurth was spokesman of the BMBF research priority programme FLASH, the first priority programme in the field of condensed matter. It was created to bundle research the at the free-electron laser within the framework of collaborative project funding.

In Wilfried Wurth’s time as scientific director of FLASH, the second light generation line and the second experimental hall of the free-electron laser were built with the FLASH II expansion project. In DESY’s strategy process, which was completed in 2018, Wilfried Wurth took a leading role in developing the visions for the future of the pioneering facility. Most recently, he led the creation of the Conceptual Design Report for its further development to FLASH2020+.

Wilfried Wurth was 62 years old and leaves behind his wife and two grown-up sons.

5-Nov-2018

When is a laser a real laser?

Photon statistics matter

Pulsed lasers are intense and coherent light sources, and the latest category is that of X-ray Free Electron Lasers (FEL), such as FLASH and the European XFEL in Hamburg or FERMI in Trieste (Italy). It is well known that coherence leads to interference phenomena which are for example visible in the famous double slit experiment by Young (spatial coherence) and interferometer experiment by Michelson (temporal coherence). First order coherence of light sources, which is manifested for example in diffraction phenomena, represents the correlation between the amplitudes of a wave at different points in space (transverse (spatial) coherence) or time (longitudinal (temporal) coherence.) However, a high degree of first order coherence is not enough to define a laser, according to the 2005 Nobel laureate Roy Glauber, who stated that a laser can be defined as a source that is coherent in all orders. The higher order correlations are between intensity at different points in time and space. How are these correlations measured? For this one has to look at the statistics of the photons.

The image shows the difference between chaotic and coherent light sources. (a) Photon correlation map for FERMI operated in seeded mode. (b) Corresponding spectrum. (c) Correlation map for FERMI operated in Self Amplified Stimulated Emission mode (the mode of operation of most Free Electron Lasers). (d) Corresponding spectrum. Reprinted from Original publication (Copyright Nature Publishing Group).

1-Aug-2018

Novel liquid jet nozzle for high repetition diffraction experiments at free-electron lasers

Rapid sample delivery for megahertz serial crystallography

A team of researchers, led by scientists from DESY, has demonstrated the successful use of a new type of liquid jet at high pulse repetition rates at FLASH. The study shows that liquid jets recover in time for the next pulse even at very short inter-pulse times of only 220 nanoseconds. Furthermore the researchers conducted the first crystal diffraction experiments using X-ray pulse repetition rates of about a million pulses per second (MHz).

The image shows microscopic images showing the interaction of the liquid jet with the X-ray beam. The last image in the sequence shows the jet after being hit by the second pulse in the pulse train. The horizontal red line indicates the position of the X-ray beam and it can be seen that the jet has recovered and is stable in the X-ray interaction region after < 290 ns. The scale bar is 20 µm. X-rays are incident from the left. (Credit: Figure from publication in IUCr, published under CC-BY-3.9)

26-Jun-2018

FLASHForward makes waves

Electron beam generates strong wakefield in plasma at DESY for the first time

The plasma accelerator project FLASHForward has reached an important milestone: in the night to 19 June, DESY physicist Jens Osterhoff and his team for the first time generated a wakefield - a kind of bow wave - in a plasma with a field strength of more than 12 gigavolts per meter using an electron beam from DESY’s FLASH accelerator. This demonstrate that it is possible to drive strong acceleration field strengths in plasma waves with FLASH that exceed the field strengths in "classic" metallic accelerator cavities by more than two orders of magnitude. The goal is to accelerate particles with the beam-generated wakefield - the milestone now reached was a critical step on the way there.

The image shows a view into the three-centimetre plasma cell of FLASHForward. Image: DESY

22-Dec-2017

Grazing light for rapid events

“X-ray streaking” allows ultrafast processes to be followed using a single pulse of light

An international team of scientists has developed a new experimental method at the FLASH X-ray laser which allows the sequence of events involved in a process to be observed using a single, ultrashort pulse of light from FLASH. Their method is called “X-ray streaking” and enables researchers to observe ultrafast processes continuously, instead of being confined to taking snapshots at discrete intervals using separate X-ray pulses. Apart from the extreme brightness of the FLASH beam, the scientists also made use of an X-ray lens which they introduced into the beamline in a particular configuration, so as to capture a chronological sequence of events using a single X-ray pulse. To demonstrate the functionality of X-ray streaking, they observed the ultrafast demagnetisation of cobalt.

The images show that the reflection signal of the sample (left), corrected by the reference signal (middle) yields the progression of the demagnetization process (right) (picture: Buzzi et al.).

14-Dec-2017

Innovation-Award on Synchrotron Radiation

The Friends of Helmholtz-Zentrum Berlin bestowed the Innovation Award upon a team of physicists from DESY, Hamburg: Dr. Bart Faatz, Dr. Evgeny Schneidmiller, Dr. Siegfried Schreiber, Dr. Markus Tischer and Dr. Mikhail Yurkov have been awarded for their work on „Innovative applications of gap-tunable undulators with integrated phase shifters in SASE x-ray FELs“.

30-Oct-2017

Imaging using incoherent light

Physicists demonstrate new method for viewing nanostructures

Physicists at the Friedrich Alexander University Erlangen-Nürnberg (FAU), the University of Hamburg and the research facility DESY have succeeded for the first time in revealing tiny structures using an imaging method that relies on the usual diffraction of light, but which does not require the scattered light to be coherent. With conventional imaging methods using the diffraction of coherent light, scientists have to go to considerable lengths to ensure the coherence of the radiation, i.e. the electromagnetic waves must remain in phase during the scattering process. The new method uses incoherent light instead. The process, which has now been demonstrated for the first time using short-wave ultraviolet radiation, stands to revolutionise the methods of diffractive optics and has been published in the journal Nature Physics.

The picture shows a diffraction image of a grating consisting of four slits, created using partially coherent light from the Free-Electron Laser Hamburg (FLASH), as used in the experiment. The coherent component of the FLASH radiation produces the horizontal diffraction pattern with a small number of pronounced maxima in its intensity; the incoherent component generates the so-called speckle pattern that can be seen above and below the coherent diffraction pattern. This is precisely the component of the light that was used by the new imaging method. Credit: Raimund Schneider et al.Beugungsbildes sichtbare sog. Speckle-Muster. Genau dieser Anteil des Lichtes wurde für die Bildgebung nach dem neuen Verfahren genutzt. Bild: Raimund Schneider et al.

30-Mai-2017

Double flashes with attosecond precision

Scientists demonstrate unparalleled phase control of free-electron laser pulses

Thanks to a smart mirror scientists can control the phase of X-rays from DESY's free-electron laser FLASH with attosecond precision. The feat enables new investigations of the interactions of light and matter, as the team headed by DESY scientist Tim Laarmann reports in the journal Nature Communications. An attosecond is a billionth of a billionth of a second.
The phase indicates at which point in its rapid oscillation a light wave is at a given point in time or space. Phase-sensitive measurements are important to gain insight of light-matter interactions and require phase-controlled pulses. Although phase control is an established technique in optics, the soft X-rays generated by FLASH oscillate a hundred times faster than visible light, requiring a hundred times better precision.

The scientists have now demonstrated phase control and interferometric autocorrelation at FLASH using pulse pairs created with a smart split-and-delay unit.

The image shows how the lamellar mirror splits the incoming X-ray pulse into two parts. The part reflected by the lower lamellae has a longer path of flight, resulting in a delay that can be adjusted with attosecond precision. Credit: Sergey Usenko, DESY

26-Mai-2017

Profiling FLASH electron bunches on a femtosecond scale

The success of FELs, having a transformative impact on science with X-rays, relies on the capability of analysing and controlling ultra-relativistic electron beams on femtosecond timescales. One major challenge is to extract tomographic electron slice parameters for each bunch instead of projected electron beam properties. A team of scientists has developed an elegant method to derive the slice emittance from snapshots of electron bunches with femtosecond resolution. Mapping of electron slice parameters and seeded FEL pulse profiles is an important ingredient for both, today's large scale facilities and future compact table-top FELs and creates new opportunities for tailored photon beam applications. The project team headed by Jörg Rossbach from the University of Hamburg, DESY photon scientist Tim Laarmann and DESY accelerator physicist Jörn Bödewadt, reports its work in the journal Scientific Reports.

The image shows the electron energy as a function of electron position (measured in fs units) in the electron bunch. The color codes the amount of electrons in the region. The spike towards lower energies is the trace left in the electron bunch by the seeded radiation process (picture: Tim Plath, UHH/DESY).

17-Feb-2017

FLASHForward accelerates first electron bunches

The plasma accelerator project FLASHForward achieved an important milestone in January: for the first time, the facility’s high-power laser accelerated electron bunches in a plasma cell. Later in the operational phase, the laser will control the formation of the plasma at FLASH. The group of scientists around DESY’s Jens Osterhoff used the laser to ignite a plasma, from which electrons were accelerated to energies of around 100 mega-electronvolts within a distance of just a few millimetres. This allows important pre-experiments for the planned beam-driven plasma experiment. As of the second half of this year, the FLASHForward scientists want to use the FLASH electron beam to generate a plasma in a plasma cell in order to further accelerate other electron bunches from the FLASH particle accelerator or electron bunches which are formed in the plasma itself.

The image shows a plasma cell in which the FLASHForward scientists accelerated the first electron bunches (photo: DESY/ H. Müller-Elsner).

6-Dec-2016

Partnership at a distance: deep-frozen helium molecules

Precise test of quantum physical tunnel effect at DESY’s X-ray laser FLASH

Helium atoms are loners. Only when you cool them to very low temperatures do they form extremely weakly bonded molecules. Yet even in this state, they are able to maintain an extremely large separation from each other thanks to quantum tunnelling. With the help of DESY’s free-electron laser FLASH, Frankfurt nuclear physicists have been able to confirm that the atoms spend more than 75 percent of their time so far apart from each other that their bond can only be explained by means of quantum tunnelling. The scientists have presented their findings in the US journal “Proceedings of the National Academy of Sciences” (PNAS).

The image above shows the experimental setup: The helium molecules are generated in an extremely cool gas stream and are separated in a diffraction grating from the rest of the gas jet. FLASH's X-rays (red) ionize both helium atoms of the molecule, causing them to separate in an explosive manner. The ions are then imaged on a location-resolving detector, symbolised by the film strip. The wave function is then reconstructed from a multitude of individual images. Credit: Reinhard Dörner / Goethe-University Frankfurt

9-Apr-2016

FLASH observes exploding xenon nanoparticles

DESY’s X-ray laser offers new insights into the interaction between light and matter

A team of researchers led by Daniela Rupp from the Technical University of Berlin has been using DESY’s X-ray laser FLASH to study the ultrafast, light-induced explosion of nanoparticles made up of xenon. Studying these so-called xenon clusters provides new insights into the fundamental interaction between intense radiation and matter, as the scientists report in the journal Physical Review Letters.

“Clusters play a fundamental role in this study,” explains Rupp. “They have a high density and at the same time, when being in the gas phase, they are extremely well isolated from their surroundings, allowing a very clean analysis of the light-matter interaction.” The researchers produced the clusters by blowing cold, pressurized xenon gas into a vacuum chamber. “In the process, the gas cools even further, first forming droplets, which then freeze and agglomerate, much like a hailstone,” describes Rupp.

The scientists then fired ultrashort, high-intensity pulses of laser light from FLASH at these tiny xenon nanoparticles, roughly 400 nanometres (millionths of a millimetre) across, whereby the radiation reached intensities of up to 500 trillion watts per square centimetre for a few trillionths of a second. By comparison: the intensity of sunlight striking the surface of the Earth is around 0.1 watts per square centimetre. The bright pulse of radiation liberated numerous electrons from the xenon atoms in the cluster, creating a plasma – a hot gas consisting of electrically charged atoms, so-called ions, with electrons racing around between them.

29-Jun-2016

DESY mourns Helen Edwards

On 21 June, Helen T. Edwards passed away at the age of 80 at her home in Illinois, USA. Helen Edwards was the chief scientist in charge of building and operating the Tevatron at the US Fermi National Accelerator Laboratory (Fermilab), and from the early 1990s onwards she played a key role in developing the TESLA superconducting accelerator technology. She maintained close ties with DESY for over three decades and was together with her husband Don an essential driving force behind years of fruitful collaboration between Fermilab and DESY.

During the early stages of the HERA project, DESY profited enormously from her experiences at Tevatron, and in the course of numerous visits to DESY Helen Edwards also contributed towards getting the proton ring accelerator up and running. In the course of the TESLA collaboration, she was behind various crucial contributions made by Fermilab towards the design of the linear collider as well as the design and construction of the TESLA Test Facility, from which FLASH later emerged. Numerous colleagues at DESY remember and value Helen Edwards from many years of collaboration, and were extremely fond of her.

With her own brand of curiosity and her desire to get to the bottom of things, she worked with accelerator physicists at DESY until shortly before her death to analyse beam effects at FLASH. She will be remembered at DESY as a competent, dedicated and open-minded scientist who was always open for discussions, and her fond memory will always be cherished. Our thoughts go out to her husband and family.

28-Apr-2016

Helmholtz Prize for science at FLASH

For their high-precision measurements carried out at DESY’s free-electron laser FLASH, five research scientists from the Goethe University in Frankfurt am Main are to receive the Helmholtz Prize in Metrology. The team surrounding Reinhard Dörner, professor for atomic physics, used a special apparatus to study extremely weakly bound helium molecules. In the process, the scientists also discovered a molecule made of three helium atoms, which had been predicted 40 years ago but which scientists had hitherto failed to find. The Helmholtz Prize, which is endowed with 20,000 euros, is awarded for outstanding achievements in metrology, the science of measurement, and is presented to European researchers every three years by the independent Helmholtz Fund.

8-Apr-2016

First user operation at FLASH2

Since Friday, 8 April at 12:14 h FLASH is running in parallel operation for two user experiments, one in the experimental hall “Albert Einstein” (FLASH1) and one in the new hall “Kai Siegbahn” (FLASH2). First official FLASH2 users are the researchers around Sven Toleikis at beamline FL24 who focus the FLASH2 pulses with the help of a multilayer mirror onto rare gas clusters and study the fluorescence of the resulting nanoplasma as a function of cluster size.

4-Sep-2015

Free-Electron Laser prize for DESY pioneers

Mikhail Yurkov and Evgeny Schneidmiller receive award at FEL Conference in South Korea

This year’s FEL Prize has been awarded to the two DESY researchers Mikhail Yurkov and Evgeny Schneidmiller at the Free-Electron Laser Conference in South Korea for their pioneering work in developing and improving free-electron lasers (FELs). The award recognises outstanding contributions to the study and development of this key future-oriented technology.

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

DESY creates new research opportunities at X-ray laser FLASH

Hamburg’s mayor Olaf Scholz and the Swedish state secretary Anders Lönn name the experimental halls

DESY opens new vistas into the nano cosmos at its pioneering X-ray laser FLASH. A comprehensive technological upgrade and expansion of the facility enables entirely new experimental opportunities and opens up groundbreaking technologies to the international scientific community. At a symbolic ceremony, Olaf Scholz, First Mayor of Hamburg, and Anders Lönn, State Secretary to Sweden’s Minister for Higher Education and Research, named the two FLASH experimental halls after the pioneer physicists and Nobel Prize winners Albert Einstein and Kai Siegbahn.
“The further technical refinement of our successful X-ray laser FLASH will now give researchers from all over the world even more precise insights into the nano cosmos,” said the Chairman of DESY’s Board of Directors, Helmut Dosch.

9-Apr-2015

FLASH looks deep into the atom

Digging into the “Giant Resonance”, scientists find hints of new quantum physics

A cooperation between theoretical and experimental physicists has uncovered previously unknown quantum states inside atoms. The results, described in a paper published today in the journal Nature Communications, allow a better understanding of some aspects of electron behaviour in atoms, which in turn could lead to better insights into technologically relevant materials.

In this study, scientists from European XFEL and the Center for Free Electron Laser Science (CFEL) at DESY examined the unknown quantum states in atoms of the noble gas xenon using DESY’s X-ray laser FLASH. The bright X-ray light of free-electron lasers such as FLASH and the European XFEL allowed the scientists to observe these states for the first time. (CFEL is a joint venture between DESY, the University of Hamburg, and the Max Planck Society.)

22-Feb-2015

15 years of FEL lasing at DESY

15 years ago, February 22nd, 2000 at 4:47 h, for the first time worldwide, lasing has been achieved with a SASE FEL at a VUV wavelength of 109 nm at the TESLA Test Facility at DESY.

The original announcement:
"It is a pleasure to inform you that on Tuesday 22nd of February, 2000, the shift crew succeeded to observe first lasing of the TTF FEL. The observed wavelength is 109 nm. The increase in intensity into the coherent angle compared to the spontaneous radiation is about 2 orders of magnitude. The width of the radiation cone is approximately 300 microradian as compared to 3 milliradian for the spontaneous radiation. The intensity of the radiation shows a strong dependency on the bunch charge. The observations are in agreement with what is expected for SASE."

The image shows the first ever measured photon beam spectrum, It has its maximum at about 109 nm. The image taken with the spectrometer's CCD is shown on the top.

4-Feb-2015

X-ray pulses uncover free nanoparticles for the first time in 3D

Research team uses DESY’s X-ray laser FLASH as a super microscope

For the first time, a German-American research team has determined the three-dimensional shape of free-flying silver nanoparticles, using DESY’s X-ray laser FLASH. The tiny particles, hundreds of times smaller than the width of a human hair, were found to exhibit an unexpected variety of shapes, as the physicists from the Technical University (TU) Berlin, the University of Rostock, the SLAC National Accelerator Laboratory in the United States and from DESY report in the scientific journal Nature Communications. Besides this surprise, the results open up new scientific routes, such as direct observation of rapid changes in nanoparticles.

20-Jan-2015

FLASH – the first optically synchronised free-electron laser

DESY light source becomes most precisely synchronised facility in the world

Scientists at DESY have developed and implemented an optical synchronisation system for the soft X-ray free-electron laser FLASH, achieving facility-wide synchronisation with femtosecond precision. The performance of the system is expected to ultimately be at least ten times better than what has been achieved anywhere so far using electronic techniques. At this level of control, ultrafast experiments can be performed systematically with the highest temporal resolution, as the team led by Holger Schlarb and Sebastian Schulz from DESY’s machine control and linear accelerator research groups and Adrian Cavalieri from the Max Planck Institute for the Structure and Dynamics of Matter reports in the journal Nature Communications.

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

FLASH2 generates first laser light

First simultaneous operation of two free-electron lasers at one particle accelerator

The FLASH II project – the extension of the free-electron laser FLASH – has reached an important milestone: On 20 August 2014, at 20:37 h, the accelerator team of the late shift was able to detect the first laser light at the new undulator line named FLASH2. Simultaneously, FLASH´s first undulator line FLASH1, which is provided with electron bunches from the same accelerator, could continue to operate without restrictions.
“This makes FLASH the world’s first free-electron laser that serves two laser lines simultaneously and independently from each other,” says project leader Bart Faatz.

The image shows the new FLASH2 undualtors.

5-Aug-2014

Every Electron Counts!

FLASH study calls for a better theory of electrons in solids

Despite years of extensive research, many unconventional electrical, thermal and magnetic properties of modern materials remain a mystery. A recent study, conducted at DESY’s free-electron laser FLASH, has now concluded that a flaw in current theories of solids hinders further understanding of complex material behavior.

21-Jul-2014

Leading scientists appointed for FLASH

Wilfried Wurth has joined the DESY team as new leading scientists.

He becomes scientific head of the free-electron laser FLASH. He has been working as a user at DESY’s light sources for a long time, and made important contributions in the field of instrumentation.

Wilfried Wurth has been professor at the University of Hamburg since 2000 and has now been appointed leading scientist at DESY as well. He focusses on X-ray spectroscopy, in particular for the investigation of ultrafast processes like the real-time observation of chemical reactions at surfaces and the dynamics of electrons in solids and at interfaces. For a long time Wurth has been one of the most prominent researchers at FLASH and, from 2007 to 2013, he was also spokesperson of the BMBF priority programme FLASH. This first priority programme in the field of condensed matter was created to bundle research at the free-electron laser within the framework of collaborative project funding. “Since the very beginning of operation, FLASH has been the pioneering free-electron laser facility in the X-ray range,” said Wurth. “I want to do my bit to make sure that FLASH will continue to be one of the world’s leading facilities for research at free-electron lasers.”

12-May-2014

Delayed explosion due to cluster shell

Hidden charge states in nanoplasmas revealed by fluorescence spectroscopy

At DESY’s X-ray laser FLASH, a team of scientists from SLAC, TU Berlin and DESY has now studied a method to delay the explosion of the sample for potentially decisive fractions of a second. Violent forces are at work during research with free-electron lasers: every single light flash brings the analysed sample to a fast explosion. In the investigation, every femtosecond (a millionth of a billionth of a second) counts when decoding the molecular structure of the sample before its destruction. In their experiments which have now been presented in the scientific journal Physical Review Letters, the scientists were able to observe the exact process that takes place in little clusters of atoms intensely irradiated by X-ray light.

11-Mar-2014

X-ray laser FLASH spies deep into giant gas planets

Study of liquid hydrogen provides important data for planetary models

Using DESY’s X-ray laser FLASH, researchers took a sneak peek deep into the lower atmospheric layers of giant gas planets such as Jupiter or Saturn. The observations of the team around lead author Dr. Ulf Zastrau from the University of Jena reveal how liquid hydrogen becomes a plasma, and provide information on the material’s thermal conductivity and its internal energy exchange, which are important ingredients for planetary models. The scientists present their experiments in Friday's issue of the scientific journal Physical Review Letters.

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

Topping-out for FLASH2 experimental hall

The building shell of the FLASH2 experimental hall is finished. On 25 September, DESY, building firms and architects celebrated the completion of the roof of the experimental hall with a traditional topping out ceremony.

17-Sep-2013

Seeding with femtosecond precision

Researchers publish results of first FEL seeding in the extreme ultraviolet range.

Researchers from the University of Hamburg and DESY for the first time have operated DESY´s free-electron laser FLASH in direct seeding mode. By overlapping short, extreme ultraviolet laser pulses with the ultra-relativistic electron bunches in their experimental setup called sFLASH, the team improved the pulse properties in intensity and length compared to unseeded FEL flashes. The method allows to create fully coherent electromagnetic radiation with high intensities and short wavelength.

22-Aug-2013

First laser-like X-ray light from a solid

Researchers open up new avenues of investigation at DESY's light source FLASH.

Researchers have for the first time created an X-ray laser based on a solid. The method developed at DESY's free-electron laser FLASH opens up new avenues of investigation in materials research, as reported by the team of Prof. Alexander Föhlisch of the Helmholtz Zentrum Berlin (HZB) in the British scientific journal "Nature." "This technology makes it possible to analyse sensitive samples that otherwise are quickly destroyed by intense X-ray light," notes co-author Prof. Wilfried Wurth of the University of Hamburg and the Hamburg Center for Free-Electron Laser Science (CFEL), a collaborative effort by DESY, the Max Planck Society and the University of Hamburg.

13-Aug-2013

Multi-photon interaction at FLASH lets electrons interfere

The behavior of atoms in strong electromagnetic fields shows often surprisingly complex results. A recent measurement at FLASH presents such complex effects. The angularly resolved photoelectron measurements show strong modulations indicating interference of electrons with high angular momenta in a multi-photon interaction.

2-Aug-2013

Wireless communication between atoms

First time-resolved measurement of Interatomic Coulombic Decay (ICD) in neon dimers.

At DESY's free-electron laser FLASH, an international team of scientists has measured the duration of a radiationless energy transfer between atoms of a neon dimer directly for the first time. The efficient redistribution of energy in molecular systems after exposure to high-energy radiation is of fundamental importance for numerous chemical and biochemical reactions.

1-Aug-2013

Hanbury Brown–Twiss interferometry explores SASE radiation at FLASH

The properties of FEL radiation are not yet fully understood, in particular, the statistical properties of FELs, which are based on self-amplified spontaneous emission (SASE). To explore this question two groups from DESY and the University of Hamburg/CFEL in collaboration with the FLASH team have performed a Hanbury Brown – Twiss (HBT) interferometry experiment at FLASH.
Hanbury Brown and Twiss, in their pioneering experiments, demonstrated that fundamental information on the statistics of light sources can be achieved by measuring intensity correlations at two separated spatial positions. In this work measurements of second- and higher-order intensity correlation functions were performed at FLASH by implementing HBT interferometry.

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