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    The DOE Science News Source is a Newswise initiative to promote research news from the Office of Science of the DOE to the public and news media.
    • 2018-04-04 18:05:05
    • Article ID: 692278

    Tick, Tock on the 'Attoclock:' Tracking X-Ray Laser Pulses at Record Speeds

    When it comes to making molecular movies, producing the world's fastest X-ray pulses is only half the battle. A new technique reveals details about the timing and energy of pulses that are less than a millionth of a billionth of a second long, which can be used to probe nature's processes at this amazingly fast attosecond timescale.

    • Credit: Terry Anderson / SLAC National Accelerator Laboratory

      In this illustration, ultrashort X-ray pulses (pink) at the Linac Coherent Light Source ionize neon gas at the center of a ring of detectors. An infrared laser (orange) sweeps the outgoing electrons (blue) across the detectors with circularly polarized light. Scientists read data from the detectors to learn about the time and energy structure of the pulses, information they will need for future experiments.

    • Credit: Frank Scholz & Jens Buck / DESY

      An illustration of the ring-shaped array of 16 individual detectors arranged in a circle like numbers on the face of a clock. An X-ray laser pulse hits a target at the center and sets free electrons that are swept around the detectors. The location, where the electrons reach the “clock,” reveals details such as the variation of the X-ray energy and intensity as a function of time within the ultrashort pulse itself.

    To catch chemistry in action, scientists at the Department of Energy’s SLAC National Accelerator Laboratory use the shortest possible flashes of X-ray light to create “molecular movies” that capture the motions of atoms in chemical reactions and reveal new details about the most fundamental processes in nature.

    Future experiments at the Linac Coherent Light Source (LCLS), SLAC’s X-ray free-electron laser, will use pulses that last just attoseconds (billionths of a billionth of a second). Such experiments will be even more powerful because they'll be able to detect the motions of electrons within molecules during chemical reactions. However, to design such ultrafast experiments, researchers need meticulous measurements of the X-ray pulses so they can use that information to interpret the data they collect on the samples they study.

    Now an international team, including SLAC scientists, has created an X-ray “attoclock” that lets them analyze X-ray pulses on the attosecond timescale of electron motions.

    “Using this method, we can resolve details of the pulses in the attosecond domain for the first time,” says Ryan Coffee, a senior scientist at LCLS and the Stanford PULSE Institute and a principal investigator on the team. “This paves the way for X-ray free-electron laser science at a timescale that is key to understanding physical chemistry.”

    The team’s research was published in Nature Photonics on March 5.

    Timekeeping in Attoseconds

    The term “attoclock” was coined by Swiss physicist Ursula Keller, who first demonstrated a technique to study attosecond processes with circularly polarized light 10 years ago. However, the LCLS version is the first one designed to measure individual X-ray pulses, one by one.

    It consists of a ring of detectors arranged like numbers on the face of a clock. When an X-ray pulse hits a target at the center of the clock, it knocks electrons out of the target's atoms. Those electrons are hit by circularly polarized laser light that whirls the electrons around the ring before they land on one of the detectors. The position of that detector – the number on the clock face – tells scientists how much energy the X-ray pulse contained and when exactly it hit the target.

    “It’s like reading a watch,” Coffee says. “An electron may strike a detector positioned at one o’clock or three o’clock or anywhere around the clock face. We can tell from where it hits exactly when it was generated by the X-ray pulse.”

    In an experiment designed to test the technique, the researchers hit neon gas with an attosecond X-ray pulse and then read which of the 16 detectors arrayed around the attoclock the freed electrons hit.

    “In coming up with this technique, we combined ideas from different fields,” says principal investigator Wolfram Helml, then a Marie Curie research fellow at SLAC and the Technical University of Munich and now at the Ludwig-Maximilian University of Munich. “For our purposes, it just made sense to combine the circularly polarized light used in the original attoclock with a ring-shaped detector that has been used in other kinds of experiments.”

    Finding the True Colors

    The technique will be especially important for pump-probe experiments, in which a molecule is first excited with a “pump” pulse and then analyzed by a second “probe” pulse to see how it reacted.

    As short as they are, these pulses can contain many different colors or wavelengths. “The color can also vary widely from pulse to pulse, and our technique can sift through the pulses, finding those that are interesting for the experiment,” Coffee says, noting the importance that such sifting will have for the data deluge expected when an upgrade to the X-ray laser, LCLS-II, comes online a couple years from now. With pulses that arrive up to a million times per second, LCLS-II will produce as much data in a few minutes as LCLS currently collects in a month.

    “For instance, only a certain color may excite a molecule when it is ‘pumped,’” Helml said. “With the attoclock we can see what part of the pulse is actually exciting the molecule because we know exactly when particular colors of light arrive. This lets us pinpoint more precisely when changes occur in the molecule as a result of the interaction with light.”

    What’s more, scientists can potentially excite individual elements in separate parts of the molecule at the same time using different colors of X-rays.

    “With this technique we could look within a single molecule at the interplay between atoms. For example, what’s going on with an oxygen atom and how might that affect the chemical environment surrounding a nearby nitrogen atom?” Helml says. “With that level of detail, we can discern completely new chemical behavior.”

    Progress in Motion

    The attoclock team is now working on a proposal to build more refined detectors.

    “With the next detector, we are aiming to precisely identify a broader spectrum of energies,” Coffee says. “This will be an important feature for our upgraded X-ray laser, LCLS-II, which will produce pulses with an even wider energy range and more multi-color flexibility than our current machine.”

    This is one of several ideas being tested at SLAC to give scientists detailed information about attosecond pulses. Two other teams are building similar systems with different types of detectors, including one at LCLS and PULSE that recently published a study in Optics Express

    The international team on the Nature Photonics study also included scientists from Deutsches Elektronen-Synchrotron (DESY) and the European X-ray Free-electron Laser (Eu-XFEL), both in Germany, who also provided the unique ring-shaped detector; University of Kassel in Germany; University of Gothenburg in Sweden; University of Bern in Switzerland; University of Colorado at Boulder; University of the Basque Country in Spain; and Lomonosov Moscow State University in Russia.

    LCLS is a DOE Office of Science user facility.


    The Stanford PULSE Institute is a joint institute of SLAC National Accelerator Laboratory and Stanford University. PULSE seeks to advance the frontiers of ultrafast science, with particular emphasis on research using SLAC's Linac Coherent Light Source (LCLS). For more information, please visit www.stanford.edu/group/pulse_institute.

    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, Calif., SLAC is operated by Stanford University for the U.S. Department of Energy's Office of Science. For more information, please visit slac.stanford.edu.

    SLAC National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

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    Researchers switch material from one state to another with a single flash of light

    Scientists from the Department of Energy's SLAC National Accelerator Laboratory and the Massachusetts Institute of Technology have demonstrated a surprisingly simple way of flipping a material from one state into another, and then back again, with single flashes of laser light.

    The Stories Behind the Science: How Does the Ocean's Saltiness Affect Tropical Storms?

    Two researchers with personal experience of hurricanes set out to investigate the role of an underestimated factor in storm's strength - salinity. They found that salinity plays a larger role than anyone thought, including them.

    Surprise finding: Discovering a previously unknown role for a source of magnetic fields

    Feature describes unexpected discovery of a role the process that seeds magnetic fields plays in mediating a phenomenon that occurs throughout the universe and can disrupt cell phone service and knock out power grids on Earth.

    Genetic behavior reveals cause of death in poplars essential to ecosystems, industry

    Scientists studying a valuable, but vulnerable, species of poplar have identified the genetic mechanism responsible for the species' inability to resist a pervasive and deadly disease. Their finding could lead to more successful hybrid poplar varieties for increased biofuels and forestry production and protect native trees against infection.

    Pushing the (Extra Cold) Frontiers of Superconducting Science

    Ames Laboratory has developed a method to measure magnetic properties of superconducting and magnetic materials that exhibit unusual quantum behavior at very low temperatures in high magnetic fields.

    Scientists Find Unusual Behavior in Topological Material

    Argonne scientists have identified a new class of topological materials made by inserting transition metal atoms into the atomic lattice of a well-known two-dimensional material.

    Wind Farms and Reducing Hurricane Precipitation

    New research reveals an unexpected benefit of large-scale offshore wind farms: the ability to lessen precipitation from hurricanes.

    New simulations confirm efficiency of waste-removal process in plasma device

    PPPL scientists have found evidence suggesting that a process could remove the unwanted ash produced during fusion reactions and make the fusion processes more efficient within a type of fusion facility known as a field-reversed configuration device.

    How Animals Use Their Tails to Swish and Swat Away Insects

    A new study shows how animals use their tails to keep mosquitoes at bay by combining a swish that blows away most of the biting bugs and a swat that kills the ones that get through.

    Missing gamma-ray blobs shed new light on dark matter, cosmic magnetism

    Scientists, including researchers from the Department of Energy's SLAC National Accelerator Laboratory, have compiled the most detailed catalog of such blobs using eight years of data collected with the Large Area Telescope (LAT) on NASA's Fermi Gamma-Ray Space Telescope. The blobs, including 19 gamma-ray sources that weren't known to be extended before, provide crucial information on how stars are born, how they die, and how galaxies spew out matter trillions of miles into space.


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    Engineering professor receives Department of Energy grant

    New Mexico State University Department of Civil Engineering Assistant Professor Ehsan Dehghan Niri has received a United States Department of Energy grant. This is a three-year award for $400,000 and is a collaboration with Arizona State University.

    AVS and AIP Publishing Expand Partnership to Launch AVS Quantum Science

    AIP Publishing and AVS: Science and Technology of Materials, Interfaces, and Processing (AVS) today announced an agreement to publish AVS Quantum Science, a new online interdisciplinary journal. The announcement coincides with the AVS 65th International Symposium & Exhibition in Long Beach, California, from October 21-26, 2018.

    Prototype Solar Energy, Battery Systems to Fuel Commercialization

    Designing, building and testing prototype systems that show how renewable energy can power devices, such as a weather and soil sensor station, can help bridge the gap between basic science research and commercialization.

    Argonne to Advance High Performance Computing in Manufacturing

    Argonne awarded funding to partner with Industry to advance the use of high performance computing in manufacturing.

    "Invisible Glass" Wins 2018 Create the Future Design Contest Grand Prize

    Scientists from the Center for Functional Nanomaterials developed a technique for making nonreflecting glass, silicon, and plastic surfaces.

    Missouri S&T researchers win multimillion dollar grant to build fast-charging stations for electric cars

    Researchers from Missouri S&T and three private companies will combine their expertise to create charging stations for electric vehicles that could charge a car in less than 10 minutes - matching the time it takes to fill up a conventional vehicle with gasoline."The big problem with electric vehicles is range, and it's not so much range as range anxiety.

    Making batteries store more energy, last longer

    A new solid polymer electrolyte may help make cell phone batteries store more energy and last longer.

    Three Brookhaven Lab Scientists Named Fellows of American Physical Society

    The American Physical Society (APS), the world's largest physics organization, has elected three scientists from the U.S. Department of Energy's (DOE) Brookhaven National Laboratory as 2018 APS fellows.

    Southern Research first to win accreditation under ISO 14034

    Southern Research has become the first organization in the United States to earn accreditation under ISO 14034, a new international standard for evaluating and verifying environmental technologies that was recently adopted by the American National Standards Institute.

    Kawtar Hafidi to head Physical Sciences and Engineering directorate at Argonne

    Physicist Kawtar Hafidi has been appointed Associate Laboratory Director, Physical Sciences and Engineering at the U.S. Department of Energy's (DOE) Argonne National Laboratory.


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    Cryocooler Cools an Accelerator Cavity

    Researchers demonstrated cryogen-free operation of a superconducting radio-frequency cavity that might ease barriers to its use in societal applications.

    Shining Light on the Separation of Rare Earth Metals

    New studies identify key molecular characteristics to potentially separate rare earth metals cleanly and efficiently with light.

    Placing Atoms for Optimum Catalysts

    Precise positioning of oxygens could help engineer faster, more efficient energy-relevant chemical transformations.

    How to Make Soot and Stardust

    Scientists unlock mystery that could help reduce emissions of fine particles from combustion engines and other sources.

    Breaking the Symmetry Between Fundamental Forces

    Scientists improve our understanding of the relationship between fundamental forces by re-creating the earliest moments of the universe.

    Water Plays Unexpected Role in Forming Minerals

    Water molecules line up tiny particles to attach and form minerals; understanding how this happens impacts energy extraction and storage along with waste disposal.

    Heavy Particles Get Caught Up in the Flow

    First direct measurement show how heavy particles containing a charm quark get caught up in the flow of early universe particle soup.

    Seeing Between the Atoms

    New detector enables electron microscope imaging at record-breaking resolution.

    Scaling Up Single-Crystal Graphene

    New method can make films of atomically thin carbon that are over a foot long.

    Discovered: Optimal Magnetic Fields Suppress Instabilities in Tokamak Plasmas

    U.S. and Korean scientists show how to find and use beneficial 3-D field perturbations to stabilize dangerous edge-localized modes in plasma.


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