Category: FLASH (DESY)

1200 participants at annual users’ meeting

1200 participants at annual users’ meeting

Record number of attendees at the joint DESY and European XFEL event

The joint meeting of users of DESY’s research light sources and the European XFEL X-ray laser once again drew a record number of attendees to Hamburg. Some 1200 participants from nearly 100 institutions from around 30 countries have registered for the three-day event (24-26 January) held at DESY, more than ever before. A particular highlight this year is the beginning of scientific user operation at the European XFEL, from which first results were presented.

“The users’ meeting in Hamburg is the largest in the world for research with X-ray light sources, and we are very proud of that,” emphasised DESY Director Helmut Dosch. “The tremendous interest reflects the importance of these unique research tools for all natural sciences and beyond.” DESY’s research director for photon science, Edgar Weckert, added: “With the X-ray lasers FLASH and European XFEL and the storage-ring-based X-ray source PETRA III, the metropolitan region offers a worldwide unique combination of high-intensity research light sources that serve a wide range of disciplines, from biology and medicine to energy, material and earth science to physics, chemistry and even art history.”

Image: DESY, Axel Heimken
Scientists measure accelerated emission

Scientists measure accelerated emission

Grazing light for rapid events

An international team, including scientists from DESY,  has verified a prediction about the quantum-mechanical behaviour of resonant systems made more than 50 years ago. In experiments at SACLA, the Japanese X-ray laser, and at the European Synchrotron Radiation Facility ESRF in France, the group led by Aleksandr Chumakov from ESRF could show a dramatic reduction in the time to emit the first X-ray photon from an ensemble of excited nuclei when the number of X-rays for the excitation was increased. This behaviour is in good agreement with one limit of a superradiant system, predicted by the US physicist Robert Dicke in 1954, as the scientists report in the journal Nature Physics.

One of the broad challenges of science is to understand the behaviour of groups of atoms based on the response of a single atom in isolation, which is usually much simpler. A facet of this is understanding the behaviour of a group of identical oscillators. An analogy is a collection of bells that all have the same tone: one can easily imagine the sound of a single bell struck once – a clear tone ringing out with a volume that decays away over time.

But what happens if one gently taps all the bells in a large collection? Will the tone be the same as a single one? What about the volume? What about the direction – does it matter where you are standing when you listen to the sound? Does it matter if you tap them all at the same time?

>Read more on the FLASH website

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

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

Grazing light for rapid events

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 invention of X-ray lasers has considerably boosted the study of the dynamics of matter. Pump-probe experiments allow artificially induced (“pumped”) processes and reactions to be photographed (“probed”) using an extremely short X-ray pulse at predetermined intervals. Ideally, these photographs, taken with different time delays, can then be assembled to create a film showing the sequence of events during an ultrafast process with a temporal resolution of the order of femtoseconds. One limitation of this otherwise promising experimental technique is, however, that the experiment has to be conducted all over again for each time delay. This means that before each observation, the process of interest must be triggered using the same starting conditions and it must run through the same sequence of events – both of which rule out extreme experimental conditions.

>Read more on the FLASH website

Image Caption: (a,b) Raw images from the reflection and reference detectors respectively. Both the images for the pumped and the un-pumped event are acquired using a single x-ray pulse. (c) Transient reflectivity image (as defined in the text) calculated from the images shown in (a,b). (d) Reshaped transient reflectivity image after calibration of the time window. Article published in Scientific Reports.

 

Scientists demonstrate unparalleled phase control of free-electron laser pulses

Scientists demonstrate unparalleled phase control of free-electron laser pulses

Double flashes with attosecond precision

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 successful transfer of a powerful optical method towards short wavelengths paves the way towards utilization of advanced nonlinear methodologies even at partially coherent free-electron lasers that rely on self-amplified spontaneous emission (SASE). Free-electron lasers (FEL) are driven by powerful particle accelerators and produce laser-like light pulses by sending bunches of fast electrons through a magnetic slalom course.

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FLASHForward accelerates first electron bunches

FLASHForward accelerates first electron bunches

The plasma accelerator project FLASHForward achieved an important milestone in January 2017.

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 electron bunches that have now been accelerated by the laser in the plasma cell have in many respects very similar properties to those that we are later hoping to accelerate with the FLASH beam in FLASHForward,” explains the project leader Jens Osterhoff.

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

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

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

Partnership at a distance: deep-frozen helium molecules

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 binding energy of a helium molecule is approximately one billionth of the binding energy of everyday molecules like oxygen or nitrogen. On top of this, the molecule is so huge that small viruses or soot particles could actually pass between the atoms. Physicists explain this in terms of quantum tunnelling. They visualise the bond in a classical molecule as a potential well, in which atoms cannot get further apart from each other than by going to opposite “walls”. However, quantum theory also allows atoms to tunnel inside these walls. “It is as if each of them were to dig a shaft without an exit,” explains Reinhard Dörner, a professor at the Institute of Nuclear Physics at the Goethe University in Frankfurt.

 

>Read more on the FLASH website

Cartoon: “When two loners are forced to share a bed, they move well beyond its edges to get away from each other.”
Credit: Peter Evers