Everything we know nowadays about novel materials and the underlying processes in them we also know thanks to studies at contemporary synchrotron facilities like BESSY II.
Here, relativistic electrons in a storage ring are employed to generate very brilliant and partly coherent light pulses from the THz to the X-ray regime in undulators and other devices. However, most of the techniques used at synchrotrons are very "photon hungry" and demand brighter and brighter light pulses to conduct innovative experiments.
The general greed for stronger light pulses does, however, not really meet the requirements of one of the most important techniques in material science: photoelectron spectroscopy. Physicists and chemists have been using it for decades to study molecules, gases and surfaces of solids.
However, if too many photons hit a surface at the same time, space charge effects deteriorate the results. Owing to these limits, certain material parameters stay hidden in such cases. Thus, a tailored temporal pattern of x-ray pulses is mandatory to move things forward in surface physics at Synchrotrons.
Scientists from HZB's Institute for Methods and Instrumentation in Synchrotron Radiation Research and the Accelerator Department have now jointly solved the gordic knot as they published in the renowned journal Nature Communications.
Their novel method is capable of picking single pulses out of a conventional pulse train as usually emitted from Synchrotron facilities. They managed to apply this for the first time to time-of-flight electron spectroscopy based on modern instruments as developed within a joint Lab with Uppsala University, Sweden.
Picking single pulses out of a pulse train
The pulse picking technique is based on a quasi resonant magnetic excitation of transverse oscillations in one specific relativistic electron bunch that – like all others – generates a radiation cone within an undulator. The selective excitation leads to an enlargement of the radiation cone. Employing a detour ("bump") in the electron beam path, the regular radiation and the radiation from the excited electrons can be easily separated and only pulses from the latter arrive – once per revolution - at the experiment. Thus, the arrival time of the pulses is now perfectly accommodated for modern high resolution time-of-flight spectrometers.
Users will be able to examine band structures with higher precision
"The development of the Pulse Picking by Resonant Excitation (PPRE) was science driven by our user community working with single bunch techniques. They demand more beamtime to improve studies on e.g. graphene, topological insulators and other "hot topics" in material science like the current debates about high Tc-Superconductors, magnetic ordering phenomena and catalytic surface effects for energy storage. Moreover, with pulse picking techniques at hand, we are now well prepared for our future light source with variable pulse lengths: BESSY-VSR, where users will appreciate pulse selection on demand to readily switch from high brightness to ultrashort pulses according to their individual needs" says Karsten Holldack, corresponding author of the paper.
First tests successful
The researchers have proven the workability of their method with ARTOF-time-of-flight spectrometers at different undulators and beamlines as well as in BESSY II's regular user mode. "Here we could certainly benefit from long year experiences with emittance manipulation", says Dr. P. Kuske acting as head of the accelerator part of the team. Thanks to accelerator developments in the past, we are capable of even picking ultrashort pulses out of the bunch trains in low-alpha operation, a special operation mode of BESSY II. At last, the users can, already right now, individually switch - within minutes – between high static flux and the single pulse without touching any settings at their instruments and the sample.
The work has now been published on May 30th 2014 in Nature Communications: Single Bunch X-ray Pulses on Demand from a Multibunch Synchrotron Radiation Source, K. Holldack et al. DOI 10.1038/ncomms5010
Dr. Karsten Holldack | Eurek Alert!
Computer model predicts how fracturing metallic glass releases energy at the atomic level
20.07.2018 | American Institute of Physics
What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
20.07.2018 | Materials Sciences