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  • richardmitnick 10:18 am on August 18, 2016 Permalink | Reply
    Tags: , New X-Ray Matter Interaction Observed at Ultra-High Intensity, SLAC LCLS,   

    From SLAC via DOE: “New X-Ray Matter Interaction Observed at Ultra-High Intensity” 

    SLAC Lab


    Basic Energy Sciences

    Previously unobserved scattering shows unexpected sensitivity to bound electrons, providing new insights into x-ray interactions with matter and opening the door to new probes of matter.

    David A. Reis
    Stanford PULSE Institute

    Artistic rendering of an intense x-ray beam interacting with metallic beryllium. In the central part of the image, two photons (white lines) interact simultaneously with a single electron of one of the beryllium atoms (sphere), emitting the electron (red streak) and a single higher energy photon (wavy blue line), while leaving the atom in an excited state (purple-blue color). Researchers found that the spectrum of the emitted high-energy photon disagreed with theoretical predictions. Image courtesy of Joel Brehm.

    The Science

    For the first time, researchers explored an extremely rare, but fundamental, process, in which two packets of light called photons scatter simultaneously from a single electron—in this case, from individual atoms in a beryllium metal target. Using the extremely high intensity x-ray laser at the Linac Coherent Light Source, they found that the details of this process deviated dramatically from expectations based on the usual assumption that the electrons behaved as quasi-free in the x-ray interaction.


    The researchers explain this anomaly in terms of a new x-ray matter interaction that they predict to have unprecedented specificity for light elements, like beryllium.

    The Impact

    In addition to providing new fundamental insights about x-ray interactions, this discovery has broad implications for understanding and controlling the fastest processes in chemical reactivity and energy conversion. The work may lead to powerful new probe techniques at x-ray free electron laser facilities to provide fundamental understanding of ultrafast chemical processes.


    The basis for atomic‐scale structure determination involves the scattering of single x‐ray photons, one at a time, from the electrons that make up all materials. Spatial resolution is achieved through a combination of the short wavelength of x-rays and the concentration of the electron density around the individual atoms. For x-ray interactions, these atomic electrons generally behave almost as if they were free. In special cases involving heavy atoms, researchers can achieve simultaneously a level of chemical specificity and spatial resolution, but this is not the case for the lighter atoms that are ubiquitous in most biological and energy-relevant materials. Thus, new methods to achieve chemical specificity for light atoms in structure determination would be revolutionary. In the current work, the researchers used the unprecedented x-ray intensity produced by the Linac Coherent Light Source x-ray laser to observe the concerted nonlinear Compton scattering of two identical hard x-ray photons from the light element beryllium to produce a single higher-energy photon. Not only did the researchers make the first observation of this fundamental process, they also observed an anomalously large shift toward longer wavelengths for the scattered photon. The large wavelength shift is indicative of an interaction that shows properties of scattering from bound (non-free) electrons, which implies that this process could be used as a chemically specific probe. Furthermore, because the nonlinear interaction requires the x-rays to coincide at precisely the same location in time and space, the mechanism is also applicable to studying the fastest processes involving electron motion in chemical reactivity and energy conversion.


    This work was supported primarily by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (BES) and the Volkswagen Foundation. Portions of this research were carried out at the Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory. Preparatory measurements were carried out at the Stanford Synchrotron Radiation Light Source (SSRL). Both LCLS and SSRL are Office of Science user facilities operated for the U.S. Department of Energy’s Office of Science by Stanford University.

    M. Fuchs, et al., Anomalous nonlinear x-ray Compton scattering. Nature Physics 11, 964 (2015). [DOI: 10.1038/nphys3452]

    See the full article here .

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  • richardmitnick 9:21 pm on August 9, 2016 Permalink | Reply
    Tags: , , SLAC LCLS, ,   

    From SLAC: “Perfection in Sight: SLAC Receives New Mirrors for X-ray Laser” 

    SLAC Lab

    August 1, 2016

    The Mirrors Only Differ by One Atom in Flatness From End to End

    SLAC engineer Corey Hardin inspects one of the newly-arrived mirrors in a clean room facility. (SLAC National Accelerator Laboratory)

    May Ling Ng, SLAC engineer, makes adjustments to the mirror restraints during a test of the holding system’s effect on mirror shape. These measurements are needed to maintain the flatness of the mirror within one atom over the entire one-meter length. (SLAC National Accelerator Laboratory)

    Scientists are installing new mirrors to improve the quality of the X-ray laser beam at the Department of Energy’s SLAC National Accelerator Laboratory.

    The meter-long mirrors are the ultimate in flatness, smooth to within the height of one atom or one-fifth of a nanometer.

    If Earth had the same surface, the hills and valleys would only vary by the width of a pencil, says Daniele Cocco, engineering physicist and head of the optics group at SLAC’s Linac Coherent Light Source (LCLS), a DOE Office of Science User Facility.

    SLAC LCLS Inside

    Right now, the mirrors are stored in a clean room to avoid dust and prevent damage. Cocco and other engineers only handle the mirrors while wearing gowns, hairnets, masks and gloves. They’re testing the mirrors to see how they will respond to heat and mechanical stress while the beam is running. Both cause tiny deformations on the surface, and even changes as small as half a nanometer can cause big problems.

    Five of these mirrors will be installed in LCLS by the beginning of next year and available for experiments in summer 2017. The new arrivals will join the 12 flat and curved mirrors that currently steer and focus light at LCLS, which is almost one mile long. Eventually, the upgraded mirror system will have a total of 28 mirrors.

    This is the first time the mirrors have been replaced at LCLS. The original mirrors were installed in 2009, when the free-electron laser came online.

    As the laser strikes the mirrors, some degradation of the reflective surface occurs over time. Since the originals were built, there have been improvements in how the mirrors are made, and engineers also better understand how the mirrors can be tailored to the LCLS beam.

    When light hits the reflective surfaces, the photons slant toward a specific point. The X-rays are shaped to the need of the experiment, from a focal spot less than a micron in diameter to as wide as a few millimeters. The beam quality also must be preserved in order to reveal the state of molecules and atoms during a range of processes that occur in biology, chemistry, materials science, and energy.

    “Time is lost when a beam isn’t perfectly uniform, and you’re not able to find the perfect spot on the sample,” Cocco says. “With mirrors this precise, it’s much easier.”

    A Japanese optics company, JTEC Corporation, fabricates the mirrors for synchrotrons and other X-ray laser research facilities such as Japan’s Spring-8 Angstrom Compact Free-Electron Laser (SACLA) and the European X-ray Free-Electron Laser (EXFEL), located in Hamburg, Germany and due to come online in 2017.

    Each mirror is made from an individual silicon crystal, artificially grown in a lab. After the mirror is polished with conventional techniques, the company uses a process called elastic emission machining, where a jet of ultra-pure water containing fine particles removes any remaining imperfections atom by atom.

    Blemishes in the mirror can create imperfections in the X-ray beam.

    “These latest mirrors preserve the beam quality within 97 percent, and the manufacturing technology is continuing to get better,” Cocco says.

    With a coherent laser beam, such as the one at LCLS, photons traveling at fixed wavelengths have a specific relationship to each other.

    “It’s not random. The light propagates as a perfect wave,” Cocco says. “Even minimal bumps alter the properties of the beam, irreversibly destroying the perfection of the wavefront.”

    The light beam also travels over a long distance, which means any disruption can amplify.

    Two of the mirrors will be installed adjacent to the front end of the undulator hall at LCLS. The other three will be located 200 meters further down the beam line, in the X-ray transport tunnel between the near and far halls.

    The mirrors will also be able to handle the higher energy range of LCLS-II, the next generation of SLAC’s X-ray laser.

    SLAC LSLS II new
    SLAC/LCLS-II work at LBL

    SLAC/LCLS-II work at FNAL

    See the full article here .

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  • richardmitnick 5:05 pm on July 15, 2016 Permalink | Reply
    Tags: , New Macromolecular Femtosecond Crystallography (MFX) station at LCLS, SLAC LCLS,   

    From SLAC: “Research Begins at SLAC’s Newest X-ray Laser Experimental Station” 

    SLAC Lab

    July 14, 2016

    In First Study, Berkeley Lab Scientists Use the New Station to Examine Hemoglobin

    Berkeley Lab and SLAC scientists (from left) Jake Koralek, Franklin Fuller, Sheraz Gul, Ernest Pastor and Jan Kern set up their experiment at the Macromolecular Femtosecond Crystallography (MFX) station at LCLS. (SLAC National Accelerator Laboratory)

    SLAC scientists Daniel Damiani and Jason Koglin in the control room of the Macromolecular Femtosecond Crystallography (MFX) station. (SLAC National Accelerator Laboratory)

    A new X-ray laser experimental station at the Department of Energy’s SLAC National Accelerator Laboratory recently welcomed its first research group, scientists from Lawrence Berkeley National Laboratory.

    Members of the Berkeley Lab’s Yachandra/Yano research team ran the inaugural experiment from July 1 to 4. They used the X-ray laser to develop new spectroscopic tools, with an initial focus on studying an enzyme in blood known as hemoglobin. Hemoglobin allows oxygen to be carried around our bodies and gives red blood cells their distinctive color.

    In contrast, Macromolecular Femtosecond Crystallography (MFX) is blaze orange, following the LCLS tradition of personalizing each instrument at SLAC’s Linac Coherent Light Source (LCLS), a DOE Office of Science User Facility. LCLS is a hard X-ray free-electron laser that fires in pulses just a few millionths of a billionth of a second in length, offering a look at chemistry on the natural timescales of reactions.

    MFX is the seventh instrument at LCLS, and is designed to optimize the facility’s ability to investigate the innermost workings of the chemistry and biology that underpin the living world. MFX allows scientists to study complex molecules such as proteins with atomic resolution using a variety of experimental techniques.

    Scientists can take advantage of short X-ray pulses at MFX to limit sample damage during exposure. This can be particularly important, for example, when looking at metal-containing molecules that are more sensitive to damage by radiation.

    During the first experiment at MFX, the Berkeley Lab group studied the distribution of electrons and the bonds between iron and the surrounding atoms within hemoglobin. Many iron-containing enzymes transfer electrons from the iron to an oxygen molecule. This makes both the metal and the oxygen highly active, leading to other important biological reactions, said Franklin Fuller, a postdoctoral researcher at Berkeley Lab.

    “We want to know where these electrons travel throughout the course of the reactions,” said Fuller. “At MFX, we can use an experimental technique – called X-ray emission spectroscopy – that is sensitive to that.”

    Using the capabilities of the X-ray laser, they could look at the chemical changes as the reactions progress. The information collected from hemoglobin experiments can also be useful when examining other iron and metal-containing proteins that are important to both energy production and health.

    Fuller said it can be difficult to measure signals from these proteins, because they exist at very low concentrations. The signals tend to be weak.

    “The goal is to push our ability to examine low concentration samples that represent real-world situations, and that requires the high brilliance, high flux of LCLS,” Fuller said.

    The group was able to collect data with excellent quality, said Jan Kern, a scientist at Berkeley Lab and LCLS. They were able to examine the relationship between the many energies in the X-ray laser beam in each shot and the X-ray spectrum from the iron-containing hemoglobin, as well as some simpler iron compounds.

    “For a first experiment using a brand new beam line, instrument and hutch, data collection went remarkably smoothly,” said Kern. “Although we were nervous about being the first users, everything worked really well. We really appreciate the work done by the LCLS scientists and engineers.”

    The number of proposals for biology experiments at LCLS has rapidly increased during the past few years. MFX will help meet this growing demand by complementing the suite of LCLS instruments already in use for structural biology studies.

    The Berkeley Lab researchers will return to MFX later in July for another experiment, designed to look closely at water splitting during photosynthesis. Learning how water is ‘split’ into protons and oxygen in photosynthetic organisms by using light is critical for designing artificial systems that are important for solar-based renewable energy. The Berkeley Lab researchers are trying to understand the mechanism using simultaneous data collection for X-ray crystallography and X-ray emission spectroscopy. To do this, the researchers built a small conveyor belt to deliver droplets of the liquid samples into the beam line at MFX.

    The new experimental station is designed to handle challenging biological samples that are fundamentally important for medicine, chemistry and energy research. MFX aims to achieve higher throughput and user access with a versatile system that supports a few standard configurations compatible with a broad range of samples.

    Scientists from across SLAC (including LCLS, the Stanford Synchrotron Radiation Lightsource (SSRL) and the Bioscience Division) designed the MFX experimental station in close consultation with the user community. The project is supported by the DOE’s Office of Biological and Environmental Research and Office of Basic Energy Sciences, both part of the DOE Office of Science, in addition to Stanford University and the NIH National Institute of General Medical Sciences.

    See the full article here .

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  • richardmitnick 11:20 am on June 16, 2016 Permalink | Reply
    Tags: Circularly polarized light, Delta undulator, , SLAC LCLS   

    From SLAC: “With Spiraling Light, SLAC X-ray Laser Offers New Glimpses of Molecules” 

    SLAC Lab

    June 15, 2016

    The side-to-side motion of electrons in a beam can be circular, elliptical, or linear, depending on the position of the Delta undulator’s magnet rows. These different motions then create circular, elliptical, or linear polarization in the light pulse. (SLAC National Accelerator Laboratory)

    A new device at the Department of Energy’s SLAC National Accelerator Laboratory allows researchers to explore the properties and dynamics of molecules with circularly polarized, or spiraling, light.

    The use of polarized light is important in the study of many molecules and processes that affect our everyday lives. It can be used to tell the difference between chiral molecules that have “left-handed” and “right-handed” variations, which affects everything from your sense of smell and taste – such as the difference between oranges and lemons, or spearmint and caraway seeds – to life-altering drugs such as thalidomide, in which one version helps ease nausea, but the other can cause abnormal limb growth in unborn children.


    The new Delta undulator produces spiraling X-ray light. (SLAC National Accelerator Laboratory)

    SLAC staff assemble the Delta undulator. (SLAC National Accelerator Laboratory)

    With the new Delta undulator, the Linac Coherent Light Source (LCLS) X-ray laser can now be tailored to look at changes in magnetic materials happening faster than a trillionth of a second, as well as fleeting processes that involve chiral compounds central to areas of biological and chemical research. LCLS is a DOE Office of Science User Facility.


    “We have already used these X-rays in a couple of studies, and the researchers seemed quite happy with the result,” said James MacArthur, a physics graduate student at Stanford University and part of the SLAC team that built the Delta undulator.

    How Spiraling Light Is Made

    LCLS generates extremely short, bright pulses of X-ray laser light by sending an electron beam through what’s called an undulator. The undulator contains pairs of magnets that force the electrons to wiggle. This motion gives off energy in the form of X-rays, which interact with the electron beam to form laser pulses that can be used for experiments.

    Before the addition of the Delta, the light delivered to experimental stations was always linearly polarized. Polarization refers to the way a light wave vibrates as it travels forward, and linearly polarized light is restricted to one direction. But circularly polarized light vibrates in two directions, producing a pattern like a corkscrew.

    With the Delta, four rows of strong magnets shift to polarize X-rays in a linear, elliptical, or circular fashion.

    Above: Electrons wiggle between two rows of magnets in a traditional undulator, creating X-rays. These X-rays, or light waves, are linearly polarized. Below: With four moving rows of magnets, the Delta undulator can create circularly polarized, or spiraling, light. (SLAC National Accelerator Laboratory)

    Scientists can use the spiraling light to reveal the orientation of molecules in certain materials, and even provide subatomic details as fine as electron distribution and spin.

    Over the past few decades, the ability to control the polarization of light has led to many breakthroughs using optical lasers. Researchers in Italy recently extended this ability into the extreme ultraviolet regime, using the FERMI Free Electron Laser. The beam at LCLS now opens doors to experiments using X-rays, which are able to probe matter in wholly new ways.

    Studies With Spiraling Light

    There are several types of experiments made possible by circularly polarized light. People who study magnetic storage for computing, for example, use spiraling light to watch magnetization changes to develop new methods and materials for faster and more compact storage devices.

    Now, with the power of the world’s strongest X-ray laser, the spiraling light can be delivered in extremely short and intense pulses over a wide range of energies.

    “We can now study the dynamics of ultrafast magnetization in a more substantive and specific way than was previously possible,” said Daniel Higley, an applied physics graduate student at Stanford. Higley is part of the Stanford Institute for Materials and Energy Sciences (SIMES), a joint institute between Stanford and SLAC.

    “One of the key things about using X-rays is that they’re quite specific, tuned to distinct energies. So we can study, in this case, what the magnetization dynamics are for individual chemical elements,” Higley said. “And the short pulses produced by an X-ray laser allow you to take a snapshot of things that happen very fast.”

    The researchers can also gather the needed data quickly. The spiraling light produced by the Delta is nearly 100 percent polarized and orders of magnitude brighter than light produced by any other type of X-ray source with such short pulses. This enables measurement of ultrafast magnetism with unprecedented accuracy and speed. The team described such measurements in a recent Review of Scientific Instruments paper.

    Scientists can also use spiraling light to probe chiral molecules, those with “right-handed” or “left-handed” structures. These subtle differences in arrangement are key to understanding the function of many substances in biological and chemical research, including certain amino acids and sugars, pharmaceuticals and pesticides.

    This light can be used to study how X-rays trigger precise, fleeting changes in chiral molecules like amino acids, and researchers can create snapshots of how radiation damages the molecular building blocks of our bodies.
    Building the Delta

    The first Delta undulator was built at Cornell nearly a decade ago. For the LCLS version, the SLAC team, led by Heinz-Dieter Nuhn, wanted to build a much bigger version of the Cornell prototype.

    But they could not copy the original exactly; it needed adjustments to work at LCLS.

    “We started with some ideas, and found they weren’t as good as we thought,” said Alberto Lutman, head of SLAC’s Delta operations team. “It took us about a year to refine the design and work out the kinks during commissioning. But as a result of all that effort, it’s gotten better and better.”

    Bringing the device up to working condition also required a large collaboration. A Cornell scientist who designed and built the first Delta undulator, Alexander Temnykh, gave input on the blueprint and initial tests. Colleagues at Germany’s DESY and the European X-ray Free-Electron Laser helped provide the measurements needed to calibrate the new equipment.

    One of the design challenges related to size. Researchers at LCLS typically use 30 to 50 meters of undulators to produce a high-quality X-ray beam.

    “The Delta undulator is only 3.2 meters long,” MacArthur said. “So we had to come up with a way to produce a lot of radiation and create a high degree of circular polarization from a short undulator.”

    In a Nature Photonics paper published in May, the Delta team reported that the undulator can produce high-intensity light at nearly 100 percent polarization.

    “It wasn’t known how well the undulator would work as we were developing it,” Lutman said. “It works, and it works nicely.”

    What’s Next for the Delta

    Research and development is underway for multiple Delta-II undulators that will produce spiraling light compatible with the beam of LCLS-II, the next generation of LCLS. LCLS-II will be 10,000 times brighter, on average, than LCLS, enabling high precision studies of even finer aspects of ultrafast magnetism and chirality.

    SLAC/LCLS-II line
    SLAC/LCLS-II line

    The Delta team will develop even more ways to manipulate polarized light. One scheme involves delivering X-rays of different energies and polarizations in a single experiment.

    “The entire Delta team has worked hard to develop a way we can produce circularly polarized light that’s custom-made for research needs,” said Mike Dunne, LCLS director. “We’re excited to be able to offer this new capability to the scientific community.”

    Citations: Lutman et al., Nature Photonics, 09 May 2016 (10.1038/nphoton.2016.79); Higley et al., Review of Scientific Instruments, 22 March 2016 (10.1063/1.4944410).

    See the full article here .

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  • richardmitnick 11:10 am on June 15, 2016 Permalink | Reply
    Tags: , , New X-ray method allows scientists to probe molecular explosions, SLAC LCLS,   

    From ANL: “New X-ray method allows scientists to probe molecular explosions” 

    Argonne Lab
    News from Argonne National Laboratory

    June 15, 2016
    Jared Sagoff

    Summer blockbuster season is upon us, which means plenty of fast-paced films with lots of action. However, these aren’t new releases from Hollywood studios; they’re one type of new “movies” of atomic-level explosions that can give scientists new information about how X-rays interact with molecules.

    A team led by researchers from the U.S. Department of Energy’s (DOE’s) Argonne National Laboratory used the high-intensity, quick-burst X-rays provided by the Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory to look at how the atoms in a molecule change when the molecule is bombarded with X-rays.


    “The LCLS gives us a unique perspective on molecular dynamics because of the extremely brief X-ray pulses that we can use,” said Antonio Picon, an Argonne X-ray scientist and lead author. “We’re able to see how charge and energy can flow through a system with amazing precision.”

    By using a new method called X-ray pump/X-ray probe, the researchers were able to excite a specifically targeted inner-shell electron in a xenon atom bonded to two fluorine atoms. After the electron was excited out of its shell, the unbalanced positive charge in the rest of the molecule caused the molecule to spontaneously dissociate in a process known as “Coulomb explosion.”

    Dynamics of the Coulomb explosion of argon clusters induced by intense femtosecond laser pulses. Kyoto University Institute for Chemical Research

    “The new X-ray pump/X-ray probe technique is so powerful because it allows us to shake the molecule at one point, and look at how it changes at a second point,” said Argonne X-ray scientist and study author Christoph Bostedt.

    The xenon difluoride molecule is only a first step for the technique. In the future, the same X-ray pump/X-ray probe method could find a broad range of applications, such as following the ultrafast structural changes that occur in light-sensitive molecules or the flow of energy in molecules. By understanding intramolecular energy flow, researchers can better develop novel materials to harness the sun’s energy, such as photovoltaics and photocatalysts.

    The new technique could also help researchers address challenges relating to the protein structure determination. For pharmaceutical studies, X-rays are often used to figure out the structures of proteins, but during that process they can also damage parts of them.

    “This technique lets you see how neighboring atoms are affected when certain regions interact with X-rays,” said Stephen Southworth, an Argonne senior X-ray scientist.

    By using an X-ray pump to excite one of the innermost electrons in the molecule, the researchers were able to target one of the electrons that is most central to and characteristic of the molecule. “This technique gives us the ability to take a series of quick snapshots to see what happens when we change a fundamental part of a molecule, and what we learn from it can inform how we approach the interactions between light and molecules in the future,” said Picon.

    The research, which was funded by the DOE Office of Science, involved a collaboration between Argonne, SLAC, and Kansas State University. “For these kinds of studies, you really need a team that combines world leaders in X-ray sources, particle detection and sample manipulation,” Southworth said.

    An article based on the study, Hetero-site-specific X-ray pump-probe spectroscopy for femtosecond intramolecular dynamics, appeared in the May 23 online edition of Nature Communications.

    See the full article here .

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  • richardmitnick 1:18 pm on May 10, 2016 Permalink | Reply
    Tags: , Experimental advance offers a first glimpse of the biophysics of vision, SLAC LCLS,   

    From U Chicago: “Experimental advance offers a first glimpse of the biophysics of vision” 

    U Chicago bloc

    University of Chicago

    May 5, 2016
    John Easton

    UChicago researchers participated in an experiment that revealed how a protein from photosynthetic bacteria changes shape in response to light in less than a trillionth of a second.
    Courtesy of SLAC National Accelerator Laboratory

    In a groundbreaking experiment using the world’s fastest camera, a team of scientists led by the University of Wisconsin-Milwaukee documented the fundamental processes of a chemical reaction as they occurred in real time. This means seeing how proteins, the building blocks of life, work in a few quadrillionths of a second.

    In a paper published* May 5 in the journal Science, the researchers describe how they acquired images of the effect of light on a tiny crystallized protein.

    Light absorption by proteins is the primary event of processes such as vision and photosynthesis that are fundamental to many life forms. The researchers focused on photoactive yellow protein, a light-absorbing component found in certain bacteria. The basic chemical process they observed, known as isomerization, also occurs when the retina in the human eye responds to light.

    Understanding how these complex molecules do their job depends on knowing the spatial arrangement of atoms and how their structure changes as they interact with light. Until now, no effective method for detailed observation of molecular movement in such detail was available. The Science paper describes an experimental first.

    “This puts us dramatically closer to understanding the chemistry necessary for all life,” said Marius Schmidt, professor of physics at UW-Milwaukee and the leader of the team. “Discovering the step-by-step process of how proteins function is necessary not only to inform treatment of disease, but also to explore the grand questions of biology.”

    “Light drives much of biology and this novel experiment is a pinnacle in understanding how living systems respond to light,” said Keith Moffat, the Louis Block Professor of Biochemistry & Molecular Biology, who pioneered this experimental approach and developed it over 25 years with his Chicago colleagues.

    The data were collected using the Linac Coherent Light [LCLS] Source X-ray free electron laser, or XFEL, at the SLAC National Accelerator Laboratory—operated by Stanford University for the U.S. Department of Energy Office of Science.


    At the speed of life

    “Biology happens at short time spans,” explained co-author Jason Tenboer, postdoctoral researcher in Schmidt’s lab. The Linac Coherent Light Source supplied the team with camera frames each lasting about 150 femtoseconds, about 1,000 times faster than any seen in an X-ray experiment before and rapid enough to allow the imaging of the fastest reactions.

    Unveiling the atomic-scale changes in protein molecules as they go about their tasks is important because these changes in structure determine their function. In 2014, Schmidt and colleagues were the first to document changes in a protein molecule over a larger increment of time.

    The scientists mapped the atoms in motion in the photoactive yellow protein as the chemical bonds of a central dye molecule—which is buried within the protein and makes it yellow—rearranged. They documented, for the first time, the structure of the yellow dye within the protein in an electronically excited state.

    For the past 60 years, the only way to examine proteins in three dimensions was with X-ray crystallography. This process shoots X-rays at crystallized proteins. These proteins diffract light and create patterns of dots the way shaking a paintbrush sprays drops on a wall. The pattern provides a fingerprint for that protein. But it is a still snapshot, a single point in time when nothing is moving.

    To capture protein molecules in action, scientists need both an optical laser and an X-ray laser with split-second pulses, which is what the XFEL provides.

    Next, the researchers hope to collect femtosecond details over a bigger range of time to create a slow-motion “movie.” This could ultimately allow scientists to intervene in the process of protein functions by using light.

    “We’re interested in the mechanism of the chemical reaction, with the goal of controlling and steering it in a certain direction with light,” Schmidt said. “We can shape laser pulses for that purpose. We will discover how the molecules march in synchronicity during such processes.”

    Forty-four researchers were involved in this study. In addition to those from UW-Milwaukee, Chicago and Stanford, members of the scientific team came from Arizona State University, Lawrence Livermore National Laboratory, University of Hamburg, State University of New York, Buffalo, University of Jyvaskyla, Max Planck Institute for Structure and Dynamics of Matter, and Imperial College, London.

    *Science paper
    Femtosecond structural dynamics drives the trans/cis isomerization in photoactive yellow protein

    See the full article here .

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  • richardmitnick 7:27 am on May 10, 2016 Permalink | Reply
    Tags: , , RIKEN SACLA, SLAC LCLS,   

    From BNL: “Ultra-fast X-ray Lasers Illuminate Elusive Atomic Spins” 

    Brookhaven Lab

    May 9, 2016
    Justin Eure
    (631) 344-2347

    Peter Genzer
    (631) 344-3174

    New x-ray technique reveals never-before-seen, trillionth-of-a-second magnetic fluctuations that transform the electronic and magnetic properties of materials.

    Brookhaven Lab physicists Pavol Juhas, John Hill, Mark Dean, Yue Cao, and Vivek Thampy, all of the Condensed Matter Physics and Materials Science Department, except Hill, who is director of NSLS-II.

    A quick flash of light can make ordinary materials extraordinary, potentially inducing qualities such as the perfect efficiency of superconductivity even at room temperature. But these subatomic transformations are infamously fleeting—they vanish in just trillionths of a second.

    Now, an international team of scientists has used synchronized infrared and x-ray laser pulses to simultaneously manipulate and reveal the ultra-fast magnetic properties of this promising quantum landscape. The rapid, light-driven switching between magnetic states, explored here with unprecedented precision, could one day revolutionize the reading and writing of data in computers and other digital devices.

    The study, published* May 9, 2016, in the journal Nature Materials, was led by scientists at the U.S. Department of Energy’s Brookhaven National Laboratory and included researchers from the U.S., China, Germany, Japan, Spain, and the UK.

    “We developed a way to reveal light-induced femtosecond magnetic dynamics in as yet unseen detail,” said Mark Dean, a physicist at Brookhaven Lab and lead author on the study. “This brings us closer to perfecting a recipe for manipulating these materials on ultra-fast time scales.”

    This novel x-ray technique, called time-resolved resonant inelastic scattering, revealed the subtle spin correlations, which travel as waves through the material and define its magnetic properties. Crucially, they behaved differently between two- and three-dimensional spaces when sparked by an infrared laser pulse.

    “Within a two-dimensional atomic plane, the novel state lasted just a few picoseconds,” said Brookhaven physicist and study coauthor Yue Cao. “But three-dimensional correlations also cross between planes, and these took hundreds of picoseconds to vanish—on this scale, that difference is tremendous. It is enormously exciting to help pioneer a new technique and see it succeed.”

    The bulk of the experimental work relied on the powerful and precise x-ray lasers available at SLAC National Accelerator Laboratory’s Linac Coherent Light Source, a DOE Office of Science User Facility, and the SACLA facility in Japan.


    SACLA Free-Electron Laser Riken Japan
    SACLA Free-Electron Laser Riken Japan

    Doping with light

    To introduce novel magnetic and electronic qualities, scientists often use a technique called chemical doping to augment the atomic configuration of a material. Electrons can be meticulously added or removed, but the process is permanent.

    “We wanted to access similar states transiently, so we used photo-doping,” Dean said. “A laser pulse supplies the needed photons, which changes the electron and spin configuration in the sample—the same spins thought to be responsible for phenomena like superconductivity. Moments later, the material returns to its native state.”

    In this work, the scientists used a strontium-iridium-oxygen compound (Sr2IrO4), selected for its strong magnetic interactions. Manipulating spin in the material was relatively easy—the real challenge was catching it in motion.

    Bright, fast flashes

    The collaboration turned to two powerful photon sources: the LCLS and SACLA, both uniquely capable of illuminating a quantum spin wave mid-stride. Both facilities can produce x-ray pulses with extremely short duration and high brightness.

    “Knowing that these facilities could produce fast and accurate enough laser pulses inspired this entire collaboration,” said study coauthor John Hill, the director of Brookhaven Lab’s National Synchrotron Light Source II, another DOE Office of Science User Facility.

    BNL NSLS-II Interior

    For the experiment, an initial infrared laser pulse struck the layered Sr2IrO4 compound, destroying the native magnetic state. For a brief moment, the electrons inside the material formed spin waves that rippled through the material and radically changed its electronic and magnetic properties. Trillionths of a second later, an x-ray pulse followed and bounced off those emergent waves. By measuring the change in both momentum and the angles of diffraction, the scientists could deduce the transient electronic and magnetic qualities.

    This specific process of bouncing and tracking x-rays, called resonant inelastic x-ray scattering (RIXS), was also pioneered by members of this collaboration to explore similar phenomena in condensed matter systems. The new research builds on that to include time-resolved data points.

    “Beyond the remarkable capabilities of LCLS and SACLA to supply ultra-short femtosecond x-ray pulses, the challenge we were facing was how to detect the response of the spins,” said study coauthor Xuerong Liu from the Institute of Physics in Beijing. “That is, we needed a specialized x-ray detection system or ‘camera.'”

    The scientists developed a highly specialized RIXS spectrometer, which used millimeter-sized silicon crystals to measure the exact energy of the rebounding x-rays.

    The data revealed a clear difference in the propagation and timescale of the magnetic phenomena, with the inter-layer correlations taking hundreds of times longer to recover than those within each layer.

    “The findings match theoretical expectations, which is encouraging, but more importantly they demonstrate the strength and precision of this technique,” said collaborator Michael Först of the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, Germany. “We can now dive deeper into the mechanism and think of strategies to fine-tune the control of magnetic properties with light.”

    Next, the scientists plan to explore optical pulses at even longer wavelengths, which will shift atoms within the material without directly exciting the electrons and spins. That work may help reveal the native magnetic coupling within the material, which in turn will clarify how to best break that coupling and toggle between different electronic and magnetic states.

    The research was funded in part by the DOE’s Office Science (BES), which supported experimentation at LCLS.

    *Science paper:
    Ultrafast energy- and momentum-resolved dynamics of magnetic correlations in the photo-doped Mott insulator Sr2IrO4

    See the full article here .

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    BNL Campus

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

  • richardmitnick 8:38 am on May 6, 2016 Permalink | Reply
    Tags: , , SLAC LCLS,   

    From DESY: “High-speed camera snaps biosensor’s rapid reaction to light” 


    X-ray study reveals ultrafast dynamics of photoactive yellow protein

    Inner structure of the photactive yellow protein 800 femtoseconds after the trans-to-cis isomerisation has been initiated by an ultrafast blue laser. The chromophore binding pocket is cut open and the chromophore itself is highlighted by the bulls eye. Credit: Marius Schmidt/University of Wisconsin-Milwaukee

    Using a high-speed X-ray camera, an international team of scientist including researchers from DESY has revealed the ultrafast response of a biosensor to light. The study, published* in the US journal Science, shows light-driven atomic motions lasting just 100 quadrillionths of a second (100 femtoseconds). The technique promises insights into the ultrafast dynamics of various light sensitive biomolecules responsible for important biological processes like photosynthesis or vision.

    The team lead by Marius Schmidt from the University of Wisconsin, Milwaukee used the LCLS X-ray laser at SLAC National Accelerator Laboratory in the U.S. to look at the light-sensitive part of a protein called photoactive yellow protein, or PYP.


    It functions as an “eye” in purple bacteria, helping them sense blue light and stay away from light that is too energetic and potentially harmful.

    For their investigation, the scientists sent a stream of tiny PYP crystals into a sample chamber. There, each crystal was struck by a flash of optical laser light and then, almost immediately after, an X-ray pulse was used to interrogate the protein’s structural response to the light at the atomic level. The structure is determined indirectly from the intricate pattern of X-ray light scattered from the crystal. By varying the time between the two pulses, scientists were able to see how the protein morphed over time. “By placing the various obtained molecular structures in order of the time delay between the optical and X-ray flashes we obtain a molecular movie of the reaction as it evolves from the first step at 100 femtoseconds to several thousand femtoseconds,” explained the first author of the paper, Kanupriya Pande, also from the University of Wisconsin and now at the Center for Free-Electron Laser Science CFEL at DESY.

    “The absorption of light leaves PYP in an excited state from which it relaxes very quickly,” explained Schmidt, the study’s principal investigator. “It does so by rearranging its atomic structure in what is known as trans-to-cis isomerisation. We’re the first to succeed in taking real-time snapshots of this type of reaction.” This type of isomerisation is also what gives vision – in that case the retinal chromophore undergoes a cis-to-trans isomerisation that ultimately leads to neuronal excitation in the eye.

    “We were able to obtain detailed structures at incredibly short time points after the initial absorption event by taking flash X-ray snapshots with the world’s brightest X-ray source,” said co-author Henry Chapman from CFEL at DESY. But, as Pande pointed out, “these are very challenging experiments, where we needed considerable innovation to assign the correct time stamps to hundreds of thousands of X-ray patterns.”

    The researchers had already studied light-induced structural changes in PYP at LCLS before, revealing atomic motions as fast as 10 billionths of a second (10 nanoseconds). By tweaking their experiment with a faster optical laser and better timing tools and sorting, they were now able to improve their speed limit 100,000 times and capture reactions in the protein that are 1,000 times faster than any seen in an X-ray experiment before.

    “The new data show for the first time how the bacterial sensor reacts immediately after it absorbs light,” says co-author Andy Aquila from SLAC. “The initial response, which is almost instantaneous, is absolutely crucial because it creates a ripple effect in the protein, setting the stage for its biological function.”

    The technique could prove valuable to unveil a number of other important ultrafast light-driven processes, for instance how visual pigments in the human eye respond to light, and how absorbing too much of it damages them; how photosynthetic organisms turn light into chemical energy, a process that could serve as a model for the development of new energy technologies; or how atomic structures respond to light pulses of different shape and duration, an important first step toward controlling chemical reactions with light.

    Together with the University of Wisconsin, Milwaukee, SLAC and DESY, the following institutions were involved in this study: Imperial College London, the University of Jyväskylä in Finland, Arizona State University, Max Planck Institute for Structure and Dynamics of Matter in Hamburg, State University of New York at Buffalo, University of Chicago, Lawrence Livermore National Laboratory and University of Hamburg.

    *Science paper:
    Femtosecond structural dynamics drives the trans/cis isomerization in photoactive yellow protein

    See the full article here .

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    DESY is one of the world’s leading accelerator centres. Researchers use the large-scale facilities at DESY to explore the microcosm in all its variety – from the interactions of tiny elementary particles and the behaviour of new types of nanomaterials to biomolecular processes that are essential to life. The accelerators and detectors that DESY develops and builds are unique research tools. The facilities generate the world’s most intense X-ray light, accelerate particles to record energies and open completely new windows onto the universe. 
That makes DESY not only a magnet for more than 3000 guest researchers from over 40 countries every year, but also a coveted partner for national and international cooperations. Committed young researchers find an exciting interdisciplinary setting at DESY. The research centre offers specialized training for a large number of professions. DESY cooperates with industry and business to promote new technologies that will benefit society and encourage innovations. This also benefits the metropolitan regions of the two DESY locations, Hamburg and Zeuthen near Berlin.

  • richardmitnick 5:46 am on April 21, 2016 Permalink | Reply
    Tags: , , SLAC LCLS,   

    From Stanford: “Peering deep into materials with ultrafast science” 

    Stanford University Name
    Stanford University

    March 31, 2016 [Just appeared in social media]
    Glenn Roberts Jr.

    New techniques developed at SLAC and Stanford allow scientists to observe changes at the nanoscale that occur in fractions of a second in response to light. This artist’s conception depicts the first step in the photovoltaic response that light produces in lead titanate.

    Laser light exposes the properties of materials used in batteries and electronics

    Creating the batteries or electronics of the future requires understanding materials that are just a few atoms thick and that change their fundamental physical properties in fractions of a second. Cutting-edge facilities at SLAC National Accelerator Laboratory and Stanford University have allowed researchers like Aaron Lindenberg to visualize properties of these nanoscale materials at ultrafast time scales.

    In one experiment, a team led by Lindenberg showed atoms shifting in trillionths of a second to produce a wrinkle in a 3-atom-thick sample of a material that might someday be used in flexible electronics. Another study observed semiconductor crystals — called “quantum dots” because they defy classical physics at the nanoscale — expand and shrink in response to ultrafast pulses of laser light.

    A three-atom-thick material wrinkles in response to a laser pulse. Understanding these dynamic ripples could provide crucial clues for the development of next-generation solar cells, electronics and catalysts.

    Revealing such intriguing properties at the nanoscale gives clues about the fundamental nature of materials and how they perform in applications we rely on for energy or information.

    “Even though some of these materials are completely embedded in everyday technologies, not a lot is understood about how they work,” says Lindenberg, who is an associate professor of materials science and engineering and of photon science. He is also a principal investigator for two SLAC/Stanford joint institutes — Stanford Institute for Materials and Energy Sciences and Stanford PULSE Institute.

    “Part of the reason some phenomena are not well understood is because they happen so fast – in billionths, trillionths or even quadrillionths of a second. For the first time, we have tools that allow us to see these things,” he says.

    Working at the intersection of materials science and engineering, Lindenberg and his team have a particular focus on finding promising materials for next-generation electronics, light-based data storage technologies and energy applications.

    “There are a broad range of new properties that emerge at the nanoscale,” Lindenberg says. “The tiniest samples, with just tens or hundreds of atoms, can have nearly flawless structures that make them ideal test tubes for very fundamental questions about what happens when a material transforms.”

    The team uses different types of laser light at SLAC and Stanford labs to learn how simple tweaks in the size, shape and design of materials can change their basic properties in unexpected ways, which could lead to new applications. Taking advantage of the powerful X-rays at SLAC facilities, including the Linac Coherent Light Source [LCLS] and the Stanford Synchrotron Radiation Lightsource [SSRL] , they explore ultrafast changes in nanoscale samples.



    “We are trying to understand how electrons or atoms move in materials, which in turn determines, for example, the efficiency of solar cells and other energy-related materials, and how materials switch between different forms,” he says. “Ultrafast techniques allow you to see these kinds of things in a completely new way.”

    See the full article here .

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    Leland and Jane Stanford founded the University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members

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  • richardmitnick 11:33 am on April 7, 2016 Permalink | Reply
    Tags: , , SLAC LCLS, World’s Fastest Electron Diffraction Snapshots of Atomic Motions in Gases   

    From SLAC: “World’s Fastest Electron Diffraction Snapshots of Atomic Motions in Gases” 

    SLAC Lab

    April 5, 2016

    Researchers have taken the world’s fastest “electron images” of rotating nitrogen molecules with SLAC’s new instrument for ultrafast electron diffraction (UED), demonstrating the technology’s potential for making real-time molecular movies of chemical reactions. (SLAC National Accelerator Laboratory)

    Ultrafast Electron Diffraction. How it works.
    This animation explains how researchers use high-energy electrons at SLAC to study ultrafast motions of atoms and molecules relevant to important material properties and chemical processes. (SLAC National Accelerator Laboratory)
    Access mp4 video here .

    High-Speed ‘Electron Camera’ Complements SLAC’s Toolbox for Studies of Ultrafast Processes in Nature

    Scientists have made a significant advance toward making movies of extremely fast atomic processes with potential applications in energy production, chemistry, medicine, materials science and more. Using a superfast, high-resolution “electron camera,” a new instrument for ultrafast electron diffraction (UED) at the Department of Energy’s SLAC National Accelerator Laboratory, researchers have captured the world’s fastest UED images of nitrogen molecules rotating in a gas, with a record shutter speed of 100 quadrillionths of a second.

    Scientists have long dreamed of watching nature’s smallest and speediest phenomena in real time. For instance, watching biomolecules facilitate life-sustaining chemical reactions at high speed and in atomic detail could teach scientists new ways of producing efficient chemical catalysts. However, most available techniques excel at speed or detail, not both.

    “Our new UED instrument can do both: It achieves an unprecedented combination of atomic resolution and extraordinary speed,” said researcher Xijie Wang, SLAC’s UED team lead and co-author of a new study published today in Nature Communications. “We’ve taken UED snapshots of atomic motions in gases faster than ever before and demonstrated the technology’s potential for making molecular movies of chemical reactions.”

    SLAC Electron Camera UED
    SLAC Electron Camera UED

    SLAC Director Chi-Chang Kao said, “UED is a major addition to the lab’s outstanding portfolio of ultrafast techniques, complementing our X-ray laser, the Linac Coherent Light Source, and enabling groundbreaking research on complex dynamic systems with wide-ranging implications for chemistry, the biosciences and future materials.” LCLS is a DOE Office of Science User Facility.

    SLAC LCLS Inside
    SLAC/LCLS Inside

    An ‘Electron Camera’ For Ultrasmall, Ultrafast Vision

    UED uses a focused beam of highly energetic electrons to probe samples – in this case, a stream of laser-excited nitrogen gas. Gases are ideal model systems for studying processes in chemistry. Electrons scatter off atoms in the sample and generate a pattern on a detector that researchers use to determine where the sample’s atoms are located. By varying the time between the laser excitation and the electron beam, which comes in very short electron bundles, scientists can track rapid changes in the pattern that correspond to quick motions of the atoms.

    While the technique itself is not new – UED has been under development by several groups throughout the world since the 1980s – it has never been done at this speed for gases.

    “When it comes to studies of gases, SLAC’s instrument is about five times faster than any other UED machine before,” said Jie Yang from the University of Nebraska, Lincoln, who led the study with Markus Guehr, a researcher at SLAC and at Potsdam University in Germany. “This leap in performance is due to the instrument’s superior high-energy electron source, which was originally developed for SLAC’s LCLS. It will help us better understand a whole new range of speedy processes on the atomic level.”

    Taking Snapshots of ‘Molecular Echoes’

    In the new study, the research team demonstrated the instrument’s superb performance by capturing the rapid rotation of nitrogen molecules in a gas.

    Each molecule consists of two nitrogen atoms connected via a strong chemical bond. As the molecules in the gas tumble around, they normally point in random directions. But hitting them with an extremely short laser pulse makes them briefly all point in the same direction. Although they quickly fall out of alignment, they periodically line up again in a sort of “molecular echo.”

    UED study of laser-induced alignment of molecules in nitrogen gas. The red curve shows how the distribution of molecular orientations in the gas changes over time. (1) Nitrogen molecules, which consist of two strongly bound nitrogen atoms, normally point in random directions when they tumble in a gas. (2) With an extremely short laser pulse, scientists orient the molecules so that they all point in the same direction. (3-6) This ordered state only lasts for a very brief moment before it disperses, but the rotating molecules periodically return to it, forming “molecular echoes” during which the nitrogen molecules align again. During the echoes, the molecules also switch rapidly from being aligned in one orientation to being aligned in another one that is perpendicular to the first (3-4 and 5-6). Using SLAC’s new UED instrument, the researchers have for the first time visualized this ultrafast transition (3-4, UED signals shown at the top) in real time and with atomic resolution. (SLAC National Accelerator Laboratory)

    “When the nitrogen molecules do line up again, they also rapidly switch from pointing in one direction to pointing in the perpendicular direction,” Yang said. “This transition takes only 300 quadrillionths of a second.” The team was able to capture this process because the “shutter speed” of the UED instrument was three times faster than the changes in alignment.

    Guehr said, “The entire process had been studied with other methods before, but our research is the first to visualize it both in real time and with a resolution detailed enough to separate the positions of the two nitrogen nuclei in the molecules.”

    Toward Movies of Chemistry in Action

    The researchers hope to use the technology in the near future to film molecules as they vibrate and watch chemical bonds break and form during chemical reactions.

    “We are also looking forward to combining UED with complementary ultrafast studies at LCLS,” Wang said. “Electrons tell us about a material’s structure, whereas X-rays tell us more about its function. Putting both together will give us a more complete picture in groundbreaking studies of all kinds of complex dynamic processes in nature.”

    The research was supported by the DOE Office of Science, the SLAC UED/UEM Initiative Program Development Fund and the National Science Foundation.

    Science Paper:
    Diffractive imaging of a rotational wavepacket in nitrogen molecules with femtosecond megaelectronvolt electron pulses

    Science team:
    Jie Yang, Markus Guehr, Theodore Vecchione, Matthew S. Robinson, Renkai Li, Nick Hartmann, Xiaozhe Shen, Ryan Coffee, Jeff Corbett, Alan Fry, Kelly Gaffney, Tais Gorkhover, Carsten Hast, Keith Jobe, Igor Makasyuk, Alexander Reid, Joseph Robinson, Sharon Vetter, Fenglin Wang, Stephen Weathersby, Charles Yoneda, Martin Centurion & Xijie Wang .


    Department of Physics and Astronomy, University of Nebraska-Lincoln, 855 N 16th Street, Lincoln, Nebraska 68588, USA
    Jie Yang, Matthew S. Robinson & Martin Centurion
    PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
    Markus Guehr
    Institute of Physics and Astronomy, Potsdam University, Potsdam 14476, Germany
    Markus Guehr
    SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
    Theodore Vecchione, Renkai Li, Nick Hartmann, Xiaozhe Shen, Ryan Coffee, Jeff Corbett, Alan Fry, Kelly Gaffney, Tais Gorkhover, Carsten Hast, Keith Jobe, Igor Makasyuk, Alexander Reid, Joseph Robinson, Sharon Vetter, Fenglin Wang, Stephen Weathersby, Charles Yoneda & Xijie Wang


    J.Y., M.G., T.V., M.S.R., R.L., X.S., T.G., F.W., S.W. and X.W. carried out the experiments. N.H., R. C., J.C., I.M., S.V. and A.F. developed the laser system. M.G. and J.Y. constructed the setup for gas phase experiments. C.H., K.J., A.R. and C.Y. helped on experimental setup. J.Y. performed the data analysis and simulations. The experiment was conceived by M.G., M.C. and X.W. The manuscript was prepared by J.Y., M.C., M.S.R. and M.G. with discussion and improvements from all authors. M.C. and X.W. supervised the work.

    See the full article here .

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    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

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