Elusive missing step in the final act of photosynthesis

After decades of effort and help from SLAC’s X-ray laser, scientists have finally seen the process by which nature creates the oxygen we breathe.

Photosynthesis plays a crucial role in shaping and sustaining life on Earth, yet many aspects of the process remain a mystery. One such mystery is how Photosystem II, a protein complex in plants, algae and cyanobacteria, harvests energy from sunlight and uses it to split water, producing the oxygen we breathe. Now researchers from the Department of Energy’s SLAC National Accelerator Laboratory and Lawrence Berkeley National Laboratory, together with collaborators from Uppsala University, Humboldt University, and other institutions have succeeded in cracking a key secret of Photosystem II.

Using SLAC’s Linac Coherent Light Source (LCLS) and the SPring-8 Angstrom Compact free electron LAser (SACLA) in Japan, they captured for the first time in atomic detail what happens in the final moments leading up to the release of breathable oxygen. The data reveal an intermediate reaction step that had not been observed before.

Find out more on the SLAC website

Filming molecular chiral dynamics from the inside with FEL

Chiral molecules are essential for understanding many aspects of chemistry, biology, and physics. A chiral molecule is non-superimposable with its mirror image and exists in two different forms called enantiomers. The reactivity and biological and pharmacological activity of chiral molecules can vary significantly depending on the configuration of the enantiomers. Understanding this property is crucial for developing technologically innovative and advanced solutions in materials science, pharmaceuticals, and catalysis.

The scientific communities of biology and chemistry have devoted significant efforts to exploring the phenomenon of chirality, yet much remains unknown about the ultrafast dynamics of chiral compounds. Time-Resolved Photo-Electron Circular Dichroism (TR-PECD) has recently emerged as a promising approach for investigating time-dependent chiral dynamics, as it enables researchers to observe the enantio-dependent structural relaxation of a molecule on a femtosecond timescale. The technique involves utilizing an ultrashort circular pulse to ionize a photo-excited molecule from the valence shell, where the transient dichroism of the medium is mapped on the forward-backward asymmetry of the photoelectron emission along the pulse propagation axis. Despite its potential, the non-local character of this approach makes the interpretation of the experimental results challenging.

Read more on the Elettra website

2023 Young Scientist Award winner announced

Dr Elke de Zitter, from the Institut de Biologie Structurale (IBS) in Grenoble, is the winner of the European XFEL Young Scientist Award 2023. The price was awarded today at the Users’ Meeting 2023 by Andrea Eschenlohr, chairwomen of the European XFEL User Organisation Executive Committee. De Zitter’s research focuses on processing serial-crystallography data taken by the SPB/SFX instrument at European XFEL. She is interested in mosquitocidal proteins, that target and kill mosquitos, the deadliest animal on Earth because of the diseases they carry. She has also worked on developing a piece of software known as Xtrapol8 which can extract protein structures from European XFEL data.

“The European XFEL Young Scientist Award highlights the future potential of young scientists working in X-ray laser science, outlining the talent, hard-work and dedication of the early-career researchers within our user community,” says Sakura Pascarelli, Scientific Director at European XFEL. “It is an opportunity to highlight the impact of new research done by talented young researchers, as well as to showcase the large collaborative efforts that are required for research at European XFEL.” 

Read more on the European XFEL website

Travel the world of light sources with our 2023 calendar

Lightsources.org is a collaboration that brings together 23 synchrotrons and 7 Free Electron Lasers located at 24 member facilities around the world. Each member facility has contributed an image for our 2023 Lightsources.org calendar.

Download your digital copy below and keep up to date with news, events, job vacancies (including PhD and postdoc positions) and proposal deadlines by subscribing to our weekly newsletter here

You can get in touch with Silvana Westbury, our Project Manager, via e-mail at: webmaster@lightsources.org

Milestone for laser technology

Research team demonstrates free-electron laser driven by plasma accelerated electron beams and seeded by additional light pulses.

Extremely intense light pulses generated by free-electron lasers (FELs) are versatile tools in research. Particularly in the X-ray range, they can be deployed to analyze the details of atomic structures of a wide variety of materials and to follow fundamental ultrafast processes with great precision. Until now, FELs such as the European XFEL in Germany are based on conventional electron accelerators, which make them long and expensive. An international team led by Synchrotron SOLEIL, France, and Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Germany, has now achieved a breakthrough on the way to an affordable alternative solution: they were able to demonstrate seeded FEL lasing in the ultraviolet regime based on a still young technology – laser-plasma acceleration. In the future, this might allow to build more compact systems, which would considerably expand the possible applications of FELs. The research collaboration presents their results in the journal Nature Photonics Nature Photonics (DOI: 10.1038/s41566-022-01104-w).

Read more on the HZDR website

Image: Together with colleagues from Synchrotron SOLEIL, LOA, PhLAM and HZDR, the German-French team succeeded for the first time in generating well-controllable laser light in a free-electron laser via plasma acceleration (Dr. Marie-Emanuelle Couprie, Dr. Arie Irman, Prof. Ulrich Schramm, Dr. Marie Labat, Dr. Amin Ghaiht, Dr. Maxwell LaBerge, Dr. Driss Oumbarek-Espinos, Dr. Alexandre Loulergue, Dr. Jurjen Couperus Cabadağ, Patrick Ufer, Dr. Yen-Yu Chang; from left to right)

Credit: HZDR/Sylvio Dittrich

Electrons and photons in a twin pack

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.

Helium, as the simplest and most accessible multi-electron system, is ideally suited for fundamental theoretical and experimental studies. Here, the mutual electrical repulsion of the two electrons plays an essential role – it accounts for a good third of the total binding energy. Of particular and fundamental interest is the interaction with photons (the quanta of light). Researchers from the groups around Christian Ott and Robert Moshammer in the division of Thomas Pfeifer at the Max Planck Institute for Nuclear Physics in Heidelberg have investigated the resonant two-photon ionisation of helium in detail at the free-electron laser FLASH of DESY in Hamburg.

Read more on the DESY website

Image: Fig. 2: Spectrum of photons unsorted (top) and sorted by peak position (bottom).

Researchers resolve decades-long debate about shock-compressed silicon with unprecedented detail

They saw how the material finds a path to contorting and flexing to avoid being irreversibly crushed.


Silicon, an element abundant in Earth’s crust, is currently the most widely used semiconductor material and is important in fields like engineering, geophysics and plasma physics. But despite decades of studies, how the material transforms when hit with powerful shockwaves has been a topic of longstanding debate.

“One might assume that because we have already studied silicon in so many ways there is nothing left to discover,” said Silvia Pandolfi, a researcher at the Department of Energy’s SLAC National Accelerator Laboratory. “But there are still some important aspects of its behavior that are not clear.”

Now, researchers at SLAC have finally put this controversy to rest, providing the first direct, high-fidelity view of how a single silicon crystal deforms during shock compression on nanosecond timescales. To do so, they studied the crystal with X-rays from SLAC’s Linac Coherent Light Source (LCLS) X-ray laser. The team published their results in Nature Communications on September 21st. What they learned could lead to more accurate models that better predict what will happen to certain materials in extreme conditions.

“This is a great example of an experiment that’s necessary to better understand certain materials,” said SLAC scientist Arianna Gleason, who was the principal investigator. “You have to start simple, with single crystals, to know what you’re tracking and understand it in really detailed ways before you can build up complexity to give way to, say, the next semiconductor of the 21st Century that will allow the electronics industry to continue the remarkable progress seen in the past 50 years.”

Read more on the SLAC website

A piece of PSI history sets off on a long journey

Safely packed in a sturdy wooden crate, a high-tech component from PSI has begun its journey to Australia. The device was in use at PSI for more than ten years – now, with the commissioning of the Swiss X-ray free-electron laser SwissFEL, it has reached the end of its service life and will be given a new task at the Australian Synchrotron in Melbourne.

The device is carefully lifted by the indoor crane. The weight displayed on the crane’s external screen shoots up and down, eventually settling down at about 11.5 tonnes. The weight of this so-called insertion device is mainly due to its heavy steel frame. The magnets installed inside this generate attractive forces of several tonnes. The device must be able to withstand this enormous field strength. In particle accelerators, the periodic arrangement of the magnets is used to deflect electrons, thereby generating synchrotron radiation – a special type of X-rays.

Pioneering work at PSI

At PSI, the insertion device was used for a very special purpose, however. Following a lecture by an American colleague on the generation of ultra-short X-ray pulses, the two PSI physicists Gerhard Ingold and Thomas Schmidt realised that the conditions at the Swiss Light Source SLS were ideal for such a technique. The technology is called femtoslicing, and it can be used to observe extremely fast processes, such as chemical reactions.

“Immediately after the lecture was over, we did our first calculations. A few days later, the calculations turned into a project and three years later, under the leadership of Gerhard Ingold, we were finally able to produce hard X-rays in the femtosecond range for the first time in the world – a pulse of high-energy X-rays lasting 0.000 000 000 000 1 second,” as the head of the Insertion Device Group at PSI, Thomas Schmidt, recalls. Their approach was based on using the powerful magnetic field produced by this device as a modulator, so as to achieve resonance between the electrons and an external infrared laser, thereby transferring the pulse length of the latter to the X-rays. Since only a small fraction of the electrons are used in this process, namely those that overlap with the laser pulse, the technique is referred to as “slicing”.

The project resulted in numerous publications. Experiments were carried out on a range of different samples and new types of detectors were developed in order to process the extremely fast units of information. These findings were ultimately crucial to the development of free electron lasers, which are driven by linear accelerators and thus indirectly also the Swiss X-ray free-electron laser SwissFEL, where the first pilot experiments were carried out in 2017. However, this also heralded the end of the Femtoslicing Facility and thus of the insertion device in question. “SwissFEL allows us to generate much brighter and even shorter pulses of this kind of radiation than with the original facility. With this, extremely fast processes can be imaged at even higher resolutions,” says Thomas Schmidt.

Since then, the insertion device has been sitting in the hall of the SLS, unused.

Important manufacturer based in Siberia

Insertion devices are high-precision instruments, and demand for them is limited. Because of this, only a few manufacturers in the world are prepared to take on the complex task of building these devices in the first place. The world’s most important supplier of superconducting wigglers (a special type of insertion device) is based in Russia. However, due to the war and the global sanctions against Russia, many countries have also stopped importing these rare devices.

“Suddenly, there was a demand for retired wigglers in our European network for synchrotron radiation sources (LEAPS – League of European Accelerator-based Photon Sources),” explains Thomas Schmidt. “First, SOLARIS, the National Synchrotron Radiation Centre in Poland, inquired about a device that was no longer needed – we immediately agreed and sent them the plans. Unfortunately, our device was not compatible with their facility.” But just a short while later, the Australian Nuclear Science and Technology Organisation got in touch, also asking for a wiggler for their synchrotron in Melbourne. Again plans were sent – and this time everything fitted.

Read more on the PSI website

Image: Thomas Schmidt in the hall of the Swiss Light Source SLS. The insertion device weighing several tonnes can be seen suspended in the background, ready for transport. After being used for research at PSI more than ten years, this high-tech device will be given a new home at the Australian Synchrotron in Melbourne.

Credit: Paul Scherrer Institute/Mahir Dzambegovic

‘Diamond rain’ on giant icy planets could be more common than previously thought

Researchers at SLAC found that oxygen boosts this exotic precipitation, revealing a new path to make nanodiamonds here on Earth.

A new study has found that “diamond rain,” a long-hypothesized exotic type of precipitation on ice giant planets, could be more common than previously thought. 

In an earlier experiment, researchers mimicked the extreme temperatures and pressures found deep inside ice giants Neptune and Uranus and, for the first time, observed diamond rain as it formed.

Investigating this process in a new material that more closely resembles the chemical makeup of Neptune and Uranus, scientists from the Department of Energy’s SLAC National Accelerator Laboratory and their colleagues discovered that the presence of oxygen makes diamond formation more likely, allowing them to form and grow at a wider range of conditions and throughout more planets.

The new study provides a more complete picture of how diamond rain forms on other planets and, here on Earth, could lead to a new way of fabricating nanodiamonds, which have a very wide array of applications in drug delivery, medical sensors, noninvasive surgery, sustainable manufacturing, and quantum electronics.

“The earlier paper was the first time that we directly saw diamond formation from any mixtures,” said Siegfried Glenzer, director of the High Energy Density Division at SLAC. “Since then, there have been quite a lot of experiments with different pure materials. But inside planets, it’s much more complicated; there are a lot more chemicals in the mix. And so, what we wanted to figure out here was what sort of effect these additional chemicals have.”

The team, led by the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and the University of Rostock in Germany, as well as France’s École Polytechnique in collaboration with SLAC, published the results today in Science Advances

Read more on the SLAC website

#SynchroLightAt75 – Operation of the PAL-XFEL in 2020

After the PAL-XFEL was opened to the public in 2017, beamtime for user service has increased every year to provide more opportunities for user experiments. In 2020, 2,819 hours were provided for user beamtime out of the planned 2,910 hours and the beam availability was 96.9%. The provided beamtime of 2,819 hours was a significant increase from 2,409 hours in 2019, as shown in Table 1. To further increase beamtime, the PAL-XFEL has plans for 24-hour operation and simultaneous operation of hard and soft X-ray beamlines in the near future.

YearPlanned BeamtimeProvided BeamtimeAvailability
20182,012 h1,921 h95.5%
20192,503 h2,409 h96.2%
20202,910 h2,819 h96.9%
Table 1. Planned and provided beamtime in 2018, 2019, and 2020

FEL saturation of 0.062 nm (20 keV) was achieved for the first time in PAL-XFEL. The measured FEL energy using the e-loss scan was 408 uJ, the FEL radiation spectrum was 25.3 eV rms (0.127% of the center photon energy), and the FEL pulse duration (FWHM) was 11 fs, which corresponds to 1×1011 photons/pulse. The e-beam energy was 10.4 GeV and the undulator K was 1.4. The undulator gap scan was conducted for 20 undulators to check the FEL saturation as shown in Figure 1. Here, quadratic undulator tapering is applied for the last 6 undulators and the calculated gain length was 3.43 m.

Figure 1. Measurement results of the saturation curve at 20 keV photon energy

Two-color FEL generation with a single electron bunch has been successfully demonstrated for the hard X-ray undulator line, broadening the research capabilities at the PAL-XFEL. Test experiments have been conducted at two photon energies, 9.7 keV and 12.7 keV. A pump pulse is generated with 8 upstream undulators of the self-seeding section and a probe pulse is generated with 12 downstream undulators of the self-seeding section. The photon energies of the pulses can be independently controlled by changing the undulator parameter K and the time delay between two pulses can be controlled from 0 to 120 femtoseconds by using the magnetic chicane installed at the self-seeding section.

Figure 2. Intensity measurement results of two-color FEL generations.

Ultra-bright hard x-ray pulses using the self-seeded FEL were applied to the demonstration of serial femtosecond crystallography (SFX) experiments in 2020. We have consistently improved the spectral purity and peak of the self-seeded FEL using a laser heater and optimized crystal conditions over a hard x-ray range from 3.5 keV to 14.6 keV. The peak brightness for self-seeded hard x-ray pulses was enhanced to almost ten times greater than that of the SASE FEL over hard x-ray ranges. For example, the peak brightness of an x-ray at 9.7 keV is 3.2×1035 photons/(s·mm2·mrad2·0.1%BW), which is the highest peak brightness ever achieved for free-electron laser pulses. Thanks to the ultra-bright x-ray pulse with narrow bandwidth and superior spectral purity, SFX experiment results using the seeded FEL showed better data quality with high resolutions compared with that using the SASE FEL. This work has been published in Nature Photonics (https://doi.org/10.1038/s41566-021-00777-z).

Figure 3. Comparison of measured FEL intensity between SASE and self-seeding FEL.

Athos just got even better

An upgrade at the soft X-ray beamline of the free electron laser SwissFEL will open up new experimental capabilities. Using an external laser system to ‘seed’ the emission of X-ray photons, and thus imprint well-defined optical properties on the beam, the upgrade gives the Athos beamline unprecedented stability. With this, ultra-fast ‘attosecond’ timescales that probe the movements of electrons in chemical reactions become possible.

Free electron lasers (FELs) in the X-ray regime, such as the X-ray free electron laser SwissFEL, produce short pulses of brilliant light that give unique insights into the structure and dynamics of materials through so-called ‘molecular movies’. The Athos beamline of SwissFEL produces so-called ‘soft’ X-rays whose comparatively low photon energies are useful for studying the interactions between molecules.

A limitation for the Athos beamline, as for almost all FELs, is stability. The reason for this comes down to the process by which light is made: a process called self-amplified spontaneous emission (SASE). In a FEL, electrons, accelerated to close to the speed of the light, are wiggled by a series of magnets, called undulators. Once wiggling, they produce photons: at SwissFEL, in the form of X-rays. SASE describes the process by which these photons repeatedly interact with the electron beam and stimulate – or ‘seed’ – the emission of more photons in subsequent parts of the electron beam. The spontaneous emission of radiation in this way is a stochastic process. This means that the X-ray beam created is inherently unstable, characterised by variations in wavelength and pulse energy.

Thanks to funding from the European Research Council (ERC), a new upgrade of Athos tackles this fundamental challenge of X-ray FELs. The upgrade forms part of the HERO project, which in 2018 was awarded a prestigious Synergy grant of 14 million Euros and incorporates principal investigators from PSI, EPFL, ETHZ and Stockholm. Standing for ‘Hidden, Entangled and Resonating Orders’, the HERO project, which is coordinated by PSI, aims to uncover hidden quantum properties in materials that cannot be studied with existing methods. The HERO upgrade of the Athos beamline will enable such new insights.

“What is demonstrated here is the power of funding for blue-skies research that the ERC uniquely provides to associated countries,” states Gabriel Aeppli, head of the Photon Science Division at PSI, who is the coordinating principal investigator for the HERO project.

Bringing Athos in line

In a classroom, one particularly well-behaved child can serve as a role model for all the children. In a similar vein, at the Athos beamline, the upgrade uses an external laser to imprint its well-behaved properties on the FEL beam. Instead of relying on the stochastic, spontaneous emission of radiation, a ‘seed-laser’ interacts with the wiggling electron beam to amplify the emission of radiation. As this external, optical laser has a well-defined pulse and coherence properties, it can transfer these to the emitted X-rays.

There is a reason that an X-ray FEL has never before been externally seeded. “Although the principle of ‘seeding’ a FEL is not entirely new, seeding a FEL at an energy range as high as this is,” explains Alexandre Trisorio, head of the gun laser group, who developed the seed-laser system. “The trouble is that there are no external laser sources that operate in the right wavelength range”.

To get around this, the scientists – through some serious feats of electron bunch gymnastics and tricks of the light – are employing a technique known as echo-enabled high-harmonic generation (EEHG), whereby higher frequency resonances are created that seed the FEL. The full upgrade is a two phase project, the first of which has now been successfully completed.

Read more on the PSI website

Image: An X-ray FEL cannot be seeded with a simple optical laser: there is none that can deliver a short enough wavelength. So, more complicated techniques are required. In a dedicated room alongside the Athos beamline, an 11m optical bench will host two titanium sapphire seed laser systems. Martin Huppert fine tunes the first of these, installed in the first phase of the HERO upgrade.

Credit: Paul Scherrer Institute / Markus Fischer

Electronic quantum dance in molecules

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 amino acid glycine is an abundant basic building block of proteins and plays part in the recognition sites on cell membranes and enzymes,“ says Laarmann. “Due to its compact nature and tendencies to form hydrogen bonds it facilitates protein folding in biomolecular reactions. Stand-alone, it is utilized as an inhibiting neurotransmitter in the central nervous system.” Glycine has also been found in space and is therefore a first signature of extra-terrestrial life. The molecular reactivity in the harsh astronomical environments is an important aspect, and in particular how isolated molecules interact with ionizing radiation is a key question in astrochemistry.

Read more on DESY website

Image: In the prump-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 an d 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

Superconducting X-ray laser reaches operating temperature colder than outer space

The facility, LCLS-II, will soon sharpen our view of how nature works on ultrasmall, ultrafast scales, impacting everything from quantum devices to clean energy.

Nestled 30 feet underground in Menlo Park, California, a half-mile-long stretch of tunnel is now colder than most of the universe. It houses a new superconducting particle accelerator, part of an upgrade project to the Linac Coherent Light Source (LCLS) X-ray free-electron laser at the Department of Energy’s SLAC National Accelerator Laboratory.

Crews have successfully cooled the accelerator to minus 456 degrees Fahrenheit – or 2 kelvins – a temperature at which it becomes superconducting and can boost electrons to high energies with nearly zero energy lost in the process. It is one of the last milestones before LCLS-II will produce X-ray pulses that are 10,000 times brighter, on average, than those of LCLS and that arrive up to a million times per second – a world record for today’s most powerful X-ray light sources.

“In just a few hours, LCLS-II will produce more X-ray pulses than the current laser has generated in its entire lifetime,” says Mike Dunne, director of LCLS. “Data that once might have taken months to collect could be produced in minutes. It will take X-ray science to the next level, paving the way for a whole new range of studies and advancing our ability to develop revolutionary technologies to address some of the most profound challenges facing our society.”

With these new capabilities, scientists can examine the details of complex materials with unprecedented resolution to drive new forms of computing and communications; reveal rare and fleeting chemical events to teach us how to create more sustainable industries and clean energy technologies; study how biological molecules carry out life’s functions to develop new types of pharmaceuticals; and peek into the bizarre world of quantum mechanics by directly measuring the motions of individual atoms.

A chilling feat

LCLS, the world’s first hard X-ray free-electron laser (XFEL), produced its first light in April 2009, generating X-ray pulses a billion times brighter than anything that had come before. It accelerates electrons through a copper pipe at room temperature, which limits its rate to 120 X-ray pulses per second.

Read more on the SLAC website

Record time resolution


After being illuminated with light, the atoms in materials react within femtoseconds, i.e. quadrillionths of a second. To observe these reactions in real time, the experiment setup used to capture them must operate with femtosecond time resolution too, otherwise the resulting images will be “blurred”. In a proof-of-principle experiment at the European XFEL, a research team has demonstrated a record time resolution of around 15 femtoseconds—the best resolution reported so far in a pump–probe experiment at an X-ray free-electron laser (FEL) facility, while keeping a high spectral resolution. “These results open up the possibility of doing time-resolved experiments with unprecedented time resolution, enabling the observation of ultrafast processes in materials that were not accessible before,” explains Daniel Rivas from European XFEL, principal investigator of the experiment and first author of the publication in the scientific journal Optica, in which the team from European XFEL and the DESY research centre in Hamburg report their results.

One of the goals of experiments at the European XFEL is to record “molecular movies”, i.e. series of snapshots of dynamic processes taken in extremely rapid succession, which reveal the details of chemical reactions or physical changes in materials at high time resolution. Understanding the molecular rearrangement during such reactions is an essential step towards controlling processes in our natural environment, such as radiation damage in biological systems or photochemical and catalytic reactions. One technique to create such movies is pump–probe spectroscopy, where an optical laser pulse (the “pump” pulse) excites a certain process in a sample and the X-ray laser pulses (the “probe” pulses) are used to take a series of snapshots in order to observe how the process evolves in time.

Read more on the European XFEL website

Image: An ultrashort X-ray pulse and an optical laser pulse interact simultaneously with a neon atom. The X-ray pulse removes an electron from the inner electronic shell and, due to the electromagnetic field of the optical laser that is present at the moment of ionization, the outcoming electron is modulated in energy.

Credit: illustratoren.de/TobiasWuestefeld in cooperation with European XFEL

If at first you don’t succeed…….

For our final Monday Montage, we focus on the benefits of perseverance and our ability as humans to dig deep and remain determined even when things are going wrong. Maximilian Obst, one of the FELBE (HZDR) users, and Michele Manfredda, from FERMI at Elettra, give honest and insightful accounts of their light source experimental experiences. Light sources are complex scientific tools. They are challenging to build, optimise and utilise. But by continuing to overcome obstacles and working as a team, great and unexpected results can appear. Often these results are obtained in the middle of the night or towards the end of a very long shift on the beamline. However, the lucky few who observe them realise they are the first people in the world to have gleaned this knowledge. Perseverance pays off!

Opening the door to X-ray quantum optics

The possibility to generate coherent copies of X-ray pulses from FELs would facilitate a realm of X-ray techniques analogous to those currently available with optical laser light. Yet, this is a challenge due to the short wavelength of X-rays. Now, researchers have devised a new solution that ‘splits’ the electron bunch prior to generation of photons, producing two perfectly coherent copies of pulses.

X-ray free electron lasers (FELs) deliver ultra-bright, ultra-short and coherent X-ray pulses. Short pulses enable time-resolved studies of phenomena such as optical switching, whilst the short wavelength of X-rays, enables experiments with clear fingerprints of atomic species, which also resolve the distances between atoms in solids and liquids. In contrast, optical spectroscopies and microscopies primarily probe electrons shared across molecules, and provide neither images at the atomic scale nor allow unique identification of atomic constituents. Thus, X-ray FELs provide essential insights for fields ranging from pharmacology to electronic device engineering.

Yet, so far, part of the picture that is missing is the ability to do experiments with two – or more – coherent copies of beams. Splitting light is par for the course in optical spectroscopies. Phase-locked pulses – pulse pairs that have a fixed phase relation, split via mirrors, enable a host of interferometric and multidimensional spectroscopies. For X-ray light, the challenge comes with the advantage: the short wavelength. The wavelength – of the order of interatomic spacings – makes it extremely challenging to split the beam using mirrors, where even the smallest path length difference introduces phase jitter.

A perfect X-ray beam splitter

Now, researchers at the SwissFEL have come up with an ingenious solution. This takes a step back in the FEL and ‘splits’ the electron bunch in the accelerator, prior to the production of photons. Collaborators from both the electron and photon ends of SwissFEL have been a feature of this project, which uses a solution from the accelerator side to meet the photon requirements.

“What is really special is that from the beginning this has been a close interaction between quantum technologists and accelerator physicists. This is really facilitated by the interdisciplinarity of PSI, and its early recognition that the current, second quantum revolution will impact its core activity of building and operating large machines”, believes Simon Gerber, head of the Quantum Photon Science Group and corresponding author in the recent publication.

Read more on the PSI website

Image: Authors (L to R) Sven Reiche, Gabriel Aeppli and Simon Gerber standing outside the entrance to the SwissFEL

Credit: Paul Scherrer Institute / Mahir Dzambegovic