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  • richardmitnick 8:14 am on September 12, 2014 Permalink | Reply
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    From SLAC: “SLAC Scientists Win Prizes for X-ray Laser Work” 


    SLAC Lab

    September 11, 2014

    Three scientists at the Department of Energy’s SLAC National Accelerator Laboratory received international prizes for their achievements in free-electron laser science, a field that has rapidly accelerated since the launch of SLAC’s X-ray laser five years ago.

    The annual prizes were awarded Aug. 27 during FEL 2014, the 36th International Free Electron Laser Conference, in Basel, Switzerland. The SLAC winners are:

    Zhirong Huang, a SLAC associate professor of photon science and PPA who has participated in pioneering projects related to the design and improvement of SLAC’s Linac Coherent Light Source (LCLS) X-ray laser, a Department of Energy Office of Science User Facility. He is a co-recipient of the 2014 FEL Prize, which recognizes significant contributions to the field.
    William Fawley, formerly of Lawrence Berkeley National Laboratory who now supports X-ray FEL R&D at SLAC, shares this year’s FEL Prize with Huang for his work in developing early FEL simulation codes, among other contributions. Fawley collaborates with the SLAC FEL theory group led by Huang, and has been working on a separate FEL project, FERMI@Elettra, in Trieste, Italy.
    Erik Hemsing, an associate staff scientist at SLAC, received the Young FEL Scientist Award for finding a new way to create beams of spiraling light, or “twisted light.”

    three
    From left, SLAC’s Erik Hemsing, Zhirong Huang and William Fawley accept awards during the 36th International Free Electron Laser Conference in Basel, Switzerland. At right is SLAC’s Paul Emma, who served as this year’s FEL Prize committee chairman. (Paul Scherrer Institute)

    “A lot of the people who have won the prize before me are my mentors and collaborators,” said Huang, who worked on X-ray FEL theory and an FEL test facility at Argonne National Laboratory before joining SLAC in 2002. “It’s a really great honor to join them.”

    Huang helped to build a “laser heater” that suppresses instability in SLAC’s linear accelerator in order for the electron bunches to emit intense X-ray light at LCLS, and he was part of the team that started up LCLS five years ago.

    More recently, he helped lead an effort to produce more intense X-ray pulses in a narrower band of wavelengths at LCLS, a process known as “self-seeding.” Huang also oversaw construction of a device that measures the duration of LCLS pulses.

    Fawley said of his award, “It is certainly a nice honor, but for me the real enjoyment is the recognition of all the work done with my collaborators” over the past several decades. He said he is probably best known in the FEL community for co-creating FEL simulation codes that supported high-power FEL research led by Lawrence Livermore National Laboratory in the 1980s and was later used to help investigate the properties of FEL designs like the LCLS. Recently, Fawley and Huang collaborated on a paper that characterizes the enhanced performance of a seeded FEL using the laser heater.

    Hemsing said, “I feel lucky to have the privilege to work alongside many of those who have made significant contributions to the FEL field over the last few decades.”

    Besides his study of twisted light, which has applications ranging from astronomy to fiber optics, Hemsing also has worked on a technique for tuning an electron beam with a laser to produce very short pulses of light with more predictable properties.

    Several new XFELs are under construction around the globe, including projects in Korea, Switzerland and Germany, adding to the XFELs already operating at SLAC and at labs in Germany and Japan.

    “I am surprised at the versatility of these machines, and at the speed at which good, new ideas are brought to reality,” Hemsing said. “It’s still a wide-open field.”

    See the full article here.

    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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  • richardmitnick 7:17 pm on September 10, 2014 Permalink | Reply
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    From SLAC- “Plastics in Motion: Exploring the World of Polymers” 


    SLAC Lab

    September 10, 2014

    Experiment Shows Potential of X-ray Laser to Study Complex, Poorly Understood Materials

    Plastics are made of polymers, which are a challenge for scientists to study. Their chainlike strands of thousands of atoms are tangled up in a spaghetti-like jumble, their motion can be measured at many time scales and they are essentially invisible to some common X-ray study techniques.

    poly
    Illustration of a polystrene molecular chain and Styrofoam cups, which are made of polystyrene. (@iStockphoto/Devonyu, Martin McCarthy)

    gel
    This photograph shows a polymer in a molten, gel-like state. (@iStockphoto/Steve Bjorklund)

    A better understanding of polymers at the molecular scale, particularly as they are cooled from a molten state to a more solid form, could lead to improved manufacturing techniques and the creation of new, customizable materials.

    In an experiment at the Department of Energy’s SLAC National Accelerator Laboratory using SLAC’s Linac Coherent Light Source (LCLS) X-ray laser, a DOE Office of Science User Facility, scientists unraveled the complex behavior of polystyrene, a popular polymer found in packing foams and plastic cups, with a sequence of ultrabright X-ray laser pulses. Their work is detailed in the Aug. 11 edition of Scientific Reports.

    SLAC LCLS
    SLAC LCLS

    They measured natural motion in polystyrene samples heated to a gel-like middle ground between their melting point and solid state. This was the first demonstration that LCLS could be used for studying polymers and a whole range of other complex materials using a technique called X-ray photon correlation spectroscopy (XPCS),

    Hyunjung Kim of Sogang University in Korea, who led this research, said, “It was unknown whether the sample would survive the exposure to the ultrabright X-ray laser pulses. However, the X-ray damage effects on the sample were weaker than expected.”

    SLAC staff scientist Aymeric Robert said, “To see how you get from something that was completely moving to something completely static is very poorly understood. Observations of how polymers move in response to temperature changes and other effects can be compared with theoretical models to predict their behavior.” Robert oversees the experimental station at LCLS that is specially designed for this X-ray technique.

    “LCLS should allow scientists to measure motion in these materials in even more detail than possible using conventional X-ray tools,” he added.

    To study motion in the heated samples, researchers embedded a matrix of nanoscale gold spheres into the polymer. Then, they recorded sequences of up to about 150 X-ray images on different sections of the sample, with the delay between images ranging from as little as seven seconds to as much as 17 minutes.

    The XPCS technique measures successive “speckle” patterns that revealed subtle changes in the position of the gold spheres relative to one another – a measure of motion within the overall sample.

    While many experiments at LCLS capture X-ray data in the instant before samples are destroyed by the intense light, this technique allows some materials to survive the effects of many X-ray pulses, which is useful for studying longer-lived properties spanning from milliseconds to minutes.

    “We showed that we could study the complex dynamics in the polymer sample even at slow time scales,” Kim said. While this experiment proved that LCLS can be used to measure the long-duration motions across the entire sample, Kim said future experiments could vary the arrangement and size of the implanted gold spheres to better gauge motion at the scale of the molecular chains. Also, faster repetition of the X-ray laser pulses could help to study motion on a shorter time scale.

    In addition to Sogang University and SLAC’s LCLS, other participating researchers were from University of California, San Diego, Argonne National Laboratory; DESY lab, The Hamburg Center for Ultrafast Imaging and the University of Siegen, in Germany; Northern Illinois University; University of Massachusetts, Amherst; and Pohang Accelerator Laboratory (PAL) in Korea. The research was supported by the National Research Foundation funded by the Ministry of Science, ICT & Future Planning of Korea, and PAL in Korea, and the Department of Energy Office of Basic Energy Sciences.

    rig
    A view of the X-ray Correlation Spectroscopy experimental station at SLAC’s Linac Coherent Light Source (LCLS) X-ray laser. This station is designed to explore polymers and other hard-to-study materials. (SLAC National Accelerator Laboratory)

    graph
    This image (a) shows the experimental setup for an X-ray photon correlation spectroscopy experiment using polymer samples at SLAC’s Linac Coherent Light Source X-ray laser. (b) This transmission electron microscopy image shows nanoscale gold spheres that were embedded in a molten polymer to help study its motion. (c) This speckle pattern was produced as X-rays struck the polymer sample. A succession of these patterns show the changing positions of the gold spheres in the polymer sample, which provides a measure of the polymer’s motion. (10.1038/srep06017)

    image
    A computerized rendering of the X-ray Correlation Spectroscopy station at SLAC’s Linac Coherent Light Source X-ray laser, which was used to study motion in polymer samples. (SLAC National Accelerator Laboratory)

    See the full article here.

    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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  • richardmitnick 1:14 pm on September 4, 2014 Permalink | Reply
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    From SLAC: “Scientists Map Protein in Living Bacterial Cells” 


    SLAC Lab

    September 3, 2014

    Experiment at SLAC’s X-ray Laser Opens Door to Exploring Cell Interiors

    Scientists have for the first time mapped the atomic structure of a protein within a living cell. The technique, which peered into cells with an X-ray laser, could allow scientists to explore some components of living cells as never before.

    The research, published Aug. 18 in Proceedings of the National Academy of Sciences, was conducted at the Department of Energy’s SLAC National Accelerator Laboratory.

    “This is a new way to look inside cells,” said David S. Eisenberg, a biochemistry professor at University of California, Los Angeles, and Howard Hughes Medical Institute investigator.

    “There are a lot of semi-ordered materials in cells where an X-ray laser could provide powerful information,” Eisenberg added. They include arrays in white blood cells that help to fight parasites and infections, insulin-containing structures in the pancreas and structures that break fatty acids and other molecules into smaller units to release energy.

    In the experiment at SLAC’s Linac Coherent Light Source X-ray laser, a DOE Office of Science User Facility, researchers probed a soil-dwelling bacterium, Bacillus thuringiensis or Bt, that is commonly used as a natural insecticide. Strains of this bacterium produce microscopic protein crystals and spores that kill insects. Normally scientists need to find ways to crystallize proteins in order to get their structures – typically a time-consuming, hit-and-miss process – but these naturally occurring crystals eliminated that step.

    SLAC LCLS Inside
    Inside the SLAC LCLS

    A liquid solution containing the living cells was jetted into the path of the ultrabright LCLS X-ray laser pulses. When a laser pulse struck a crystal, it created a pattern of diffracted X-ray light. More than 30,000 of these patterns were combined and analyzed by sophisticated software to reproduce the detailed 3-D structure of the protein.

    Many of the bacterial cells likely ruptured and spewed their crystal contents as they flew at high speed toward the X-rays. But because it took just thousandths of a second for the cells to reach the X-ray pulses, it’s very likely that many of the X-ray images showed protein crystals that were still inside the cells, the researchers concluded.

    three
    Three scenarios suggesting how the integrity of Bacillus thuringiensis (Bt) cells studied at the Linac Coherent Light Source X-ray laser might vary at the moment they are struck by X-rays. The horizontal arrow depicts the flow of the cell samples from a liquid jet to waste collection. The left, middle, and right columns depict three different time points along the liquid jet’s stream. Depending on the rate of cell rupture and the flow rate of the jet, the crystals may arrive at the interaction point either (1) inside intact cells, (2) inside ruptured (“lysed”) cells, or (3) outside of ruptured cells. (10.1073/pnas.1413456111)

    Importantly, Eisenberg said, “The rest of the cell contents don’t obscure the results.”

    In addition, the 3-D structure of proteins obtained from the crystals in living bacteria cells was essentially identical to that obtained through other methods. Earlier studies had already shown that LCLS can be used to study smaller, easier-to-produce crystals than traditional X-ray sources require, although it typically requires a far larger volume of crystals to achieve atomic-scale resolution.

    In an LCLS study published in 2012, a separate team of researchers used protein crystals grown inside live insect cells to study a potential weak spot in a parasite responsible for a disease called African sleeping sickness. But in that experiment they extracted the crystals rather than attempting to study them inside cells.

    Eisenberg said possible next steps include improving the technique by developing new sample-delivery methods that are gentler to the cells’ structure, and producing faster X-ray pulse rates that capture more images and yield even better results.

    “I think this whole area of science is going to continue growing,” he said.

    In addition to UCLA and LCLS, other researchers participating in the study were from Lawrence Berkeley National Laboratory; Arizona State University; University of California, Riverside; the Institute of Structural Biology in France; and the Max Planck Institute for Medical Research in Germany. The research was supported by the U.S. Department of Energy Office of Science, Howard Hughes Medical Institute, Max Planck Society, the National Institutes of Health, the Keck Foundation and the National Science Foundation.

    See the full article here.

    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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  • richardmitnick 1:23 pm on August 26, 2014 Permalink | Reply
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    From SLAC: “X-ray Laser Probes Tiny Quantum Tornadoes in Superfluid Droplets” 


    SLAC Lab

    August 21, 2014

    An experiment at the Department of Energy’s SLAC National Accelerator Laboratory revealed a well-organized 3-D grid of quantum “tornadoes” inside microscopic droplets of supercooled liquid helium – the first time this formation has been seen at such a tiny scale.

    image
    In this illustration, a patterned 3-D grid of tiny whirlpools, called quantum vortices, populates a nanoscale droplet of superfluid helium. Researchers found that in a micron-sized droplet, the density of vortices was 100,000 times greater than in any previous experiment on superfluids. An artistic rendering of a wheel-shaped droplet can be seen in the distance. (SLAC National Accelerator Laboratory)

    The findings by an international research team provide new insight on the strange nanoscale traits of a so-called “superfluid” state of liquid helium. When chilled to extremes, liquid helium behaves according to the rules of quantum mechanics that apply to matter at the smallest scales and defy the laws of classical physics. This superfluid state is one of just a few examples of quantum behavior on a large scale that makes the behavior easier to see and study.

    The results, detailed in the Aug. 22 issue of Science, could help shed light on similar quantum states, such as those in superconducting materials that conduct electricity with 100 percent efficiency or the strange collectives of particles, dubbed Bose-Einstein condensates, which act as a single unit.

    “What we found in this experiment was really surprising. We did not expect the beauty and clarity of the results,” said Christoph Bostedt, a co-leader of the experiment and a senior scientist at SLAC’s Linac Coherent Light Source (LCLS), the DOE Office of Science User Facility where the experiment was conducted.

    machine
    This instrument, called CAMP, was used for the helium nanodroplets experiment at the Linac Coherent Light Source’s Atomic, Molecular and Optical Science (AMO) experimental station. (SLAC National Accelerator Laboratory)

    “We were able to see a manifestation of the quantum world on a macroscopic scale,” said Ken Ferguson, a PhD student from Stanford University working at LCLS.

    While tiny tornadoes had been seen before in chilled helium, they hadn’t been seen in such tiny droplets, where they were packed 100,000 times more densely than in any previous experiment on superfluids, Ferguson said.

    Studying the Quantum Traits of a Superfluid

    Helium can be cooled to the point where it becomes a frictionless substance that remains liquid well below the freezing point of most fluids. The light, weakly attracting atoms have an endless wobble – a quantum state of perpetual motion that prevents them from freezing. The unique properties of superfluid helium, which have been the subject of several Nobel prizes, allow it to coat and climb the sides of a container, and to seep through molecule-wide holes that would have held in the same liquid at higher temperatures.

    In the LCLS experiment, researchers jetted a thin stream of helium droplets, like a nanoscale string of pearls, into a vacuum. Each droplet acquired a spin as it flew out of the jet, rotating up to 2 million turns per second, and cooled to a temperature colder than outer space. The X-ray laser took snapshots of individual droplets, revealing dozens of tiny twisters, called “quantum vortices,” with swirling cores that are the width of an atom.

    The fast rotation of the chilled helium nanodroplets caused a regularly spaced, dense 3-D pattern of vortices to form. This exotic formation, which resembles the ordered structure of a solid crystal and provides proof of the droplets’ quantum state, is far different than the lone whirlpool that would form in a regular liquid, such as briskly stirred cup of coffee.

    More Surprises in Store

    Researchers also discovered surprising shapes in some superfluid droplets. In a normal liquid, droplets can form peanut shapes when rotated swiftly, but the superfluid droplets took a very different form. About 1 percent of them formed unexpected wheel-like shapes and reached rotation speeds never before observed for their classical counterparts.

    Oliver Gessner, a senior scientist at Lawrence Berkeley Laboratory and a co-leader in the experiment, said, “Now that we have shown that we can detect and characterize quantum rotation in helium nanodroplets, it will be important to understand its origin and, ultimately, to try to control it.”

    Andrey Vilesov of the University of Southern California, the third experiment co-leader, added, “The experiment has exceeded our best expectations. Attaining proof of the vortices, their configurations in the droplets and the shapes of the rotating droplets was only possible with LCLS imaging.”

    He said further analysis of the LCLS data should yield more detailed information on the shape and arrangement of the vortices: “There will definitely be more surprises to come.”

    Other research collaborators were from the Stanford PULSE Institute; University of California, Berkeley; the Max Planck Society; Center for Free-Electron Laser Science at DESY; PNSensor GmbH; Chinese University of Hong Kong; and Kansas State University. This work was supported by the National Science Foundation, the U.S. Department of Energy Office of Science and the Max Planck Society.

    See the full article here.

    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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  • richardmitnick 4:09 pm on August 21, 2014 Permalink | Reply
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    From Berkeley Lab: “Researchers Map Quantum Vortices Inside Superfluid Helium Nanodroplets” 

    Berkeley Logo

    Berkeley Lab

    August 21, 2014
    Kate Greene

    Scientists have, for the first time, characterized so-called quantum vortices that swirl within tiny droplets of liquid helium. The research, led by scientists at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), the University of Southern California, and SLAC National Accelerator Laboratory, confirms that helium nanodroplets are in fact the smallest possible superfluidic objects and opens new avenues for studying quantum rotation.

    “The observation of quantum vortices is one of the most clear and unique demonstrations of the quantum properties of these microscopic objects,” says Oliver Gessner, senior scientist in the Chemical Sciences Division at Berkeley Lab. Gessner and colleagues, Andrey Vilesov of the University of Southern California and Christoph Bostedt of SLAC National Accelerator Laboratory at Stanford, led the multi-facility and multi-university team that published the work this week in Science.

    Droplet_art_fin3drop
    Illustration of analysis of superfluid helium nanodroplets. Droplets are emitted via a cooled nozzle (upper right) and probed with x-ray from the free-electron laser. The multicolored pattern (upper left) represents a diffraction pattern that reveals the shape of a droplet and the presence of quantum vortices such as those represented in the turquoise circle with swirls (bottom center). Credit: Felix P. Sturm and Daniel S. Slaughter, Berkeley Lab.

    The finding could have implications for other liquid or gas systems that contain vortices, says USC’s Vilesov. “The quest for quantum vortices in superfluid droplets has stretched for decades,” he says. “But this is the first time they have been seen in superfluid droplets.”

    Superfluid helium has long captured scientist’s imagination since its discovery in the 1930s. Unlike normal fluids, superfluids have no viscosity, a feature that leads to strange and sometimes unexpected properties such as crawling up the walls of containers or dripping through barriers that contained the liquid before it transitioned to a superfluid.

    Helium superfluidity can be achieved when helium is cooled to near absolute zero (zero kelvin or about -460 degrees F). At this temperature, the atoms within the liquid no longer vibrate with heat energy and instead settle into a calm state in which all atoms act together in unison, as if they were a single particle.

    For decades, researchers have known that when superfluid helium is rotated–in a little spinning bucket, say–the rotation produces quantum vortices, swirls that are regularly spaced throughout the liquid. But the question remained whether anyone could see this behavior in an isolated, nanoscale droplet. If the swirls were there, it would confirm that helium nanodroplets, which can range in size from tens of nanometers to microns, are indeed superfluid throughout and that the motion of the entire liquid drop is that of a single quantum object rather than a mixture of independent particles.

    But measuring liquid flow in helium nanodroplets has proven to be a serious challenge. “The way these droplets are made is by passing helium through a tiny nozzle that is cryogenically cooled down to below 10 Kelvin,” says Gessner. “Then, the nanoscale droplets shoot through a vacuum chamber at almost 200 meters-per-second. They live once for a few milliseconds while traversing the experimental chamber and then they’re gone. How do you show that these objects, which are all different from one another, have quantum vortices inside?”

    og
    Oliver Gessner, Chemical Sciences Division, Berkeley Lab. Credit: Roy Kaltschmidt

    The researchers turned to a facility at SLAC called the Linac Coherent Light Source (LCLS), a DOE Office of Science user facility that is the world’s first x-ray free-electron laser. This laser produces very short light pulses, lasting just a ten-trillionth of a second, which contain a huge number of high-energy photons. These intense x-ray pulses can effectively take snapshots of single, ultra-fast, ultra-small objects and phenomena.

    slac
    Inside the SLAC LCLS

    “With the new x-ray free electron laser, we can now image phenomenon and look at processes far beyond what we could imagine just a decade ago,” says Bostedt of SLAC. “Looking at the droplets gave us a beautiful glimpse into the quantum world. It really opens the door to fascinating sciences.”

    In the experiment, the researchers blasted a stream of helium nanodroplets across the x-ray laser beam inside a vacuum chamber; a detector caught the pattern that formed when the x-ray light diffracted off the drops.

    The diffraction patterns immediately revealed that the shape of many droplets were not spheres, as was previously assumed. Instead, they were oblate. Just as the Earth’s rotation causes it to bulge at the equator, so too do rotating nanodroplets expand around the middle and flatten at the top and bottom.

    But the vortices themselves are invisible to x-ray diffraction, so the researchers used a trick of adding xenon atoms to the droplets. The xenon atoms get pulled into the vortices and cluster together.

    “It’s similar to pulling the plug in a bathtub and watching the kids’ toys gather in the vortex,” says Gessner. The xenon atoms diffract x-ray light much stronger than the surrounding helium, making the regular arrays of vortices inside the droplet visible. In this way, the researchers confirmed that vortices in nanodroplets behave as those found in larger amounts of rotating superfluid helium.

    Armed with this new information, the researchers were able to determine the rotational speed of the nanodroplets. They were surprised to find that the nanodroplets spin up to 100,000 times faster than any other superfluid helium sample ever studied in a laboratory.

    Moreover, while normal liquid drops will change shape as they spin faster and faster–to resemble a peanut or multi-lobed globule, for instance–the researchers saw no evidence of such shapeshifting in the helium nanodroplets. “Essentially, we’re exploring a new regime of quantum rotation with this matter,” Gessner says.

    “It’s a new kind of matter in a sense because it is a self-contained isolated superfluid,” he adds. “It’s just all by itself, held together by its own surface tension. It’s pretty perfect to study these systems if one wants to understand superfluidity and isolate it as much as possible.”

    This research was supported by the DOE Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences and Biosciences Division as well as the National Science Foundation.

    See the full article here.

    A U.S. Department of Energy National Laboratory Operated by the University of California

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  • richardmitnick 10:12 am on August 7, 2014 Permalink | Reply
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    From Slac Lab: “Catching Chemistry in Motion” 


    SLAC Lab

    August 6, 2014
    Laser-timing Tool Works at the Speed of Electrons

    Researchers at the Department of Energy’s SLAC National Accelerator Laboratory have developed a laser-timing system that could allow scientists to take snapshots of electrons zipping around atoms and molecules. Taking timing to this new extreme of speed and accuracy at the Linac Coherent Light Source X-ray laser, a DOE Office of Science user facility, will make it possible to see the formative stages of chemical reactions.

    “Previously, we could see a chemical bond before it’s broken and after it’s broken,” said Ryan Coffee, an LCLS scientist whose team developed this system. “With this tool, we can watch the bond while it is breaking and ‘freeze-frame’ it.”

    The success of most LCLS experiments relies on precise timing of the X-ray laser with another laser, a technique known as “pump-probe.” Typically, light from an optical laser “pumps” or triggers a specific effect in a sample, and researchers vary the arrival of the X-ray laser pulses, which serve as the “probe” to capture images and other data that allow them to study the effects at different points in time.

    Pump-probe experiments at LCLS are used to study a wide range of processes at the atomic or molecular scale, including studies of biological samples and exotic materials like high-temperature superconductors.

    But LCLS X-ray pulses are tricky to control. They have inherent jitter that causes them to fluctuate in arrival time, energy, position, duration and the wavelength of their light.

    There are several tools and techniques that scientists use to understand and limit the impacts of jitter on experiments, and timing tools counter the arrival-time jitter by offering very precise measurements. These measurements can help scientists to interpret their data by pinpointing the timing of changes they see in samples after they are exposed to the first laser pulse. Some experiments would not be possible without precise timing tools because of the ultrafast scale of the changes they are trying to observe.

    Achieving ‘Attosecond’ Experiments

    tool
    An illustration of the setup used to test an “attosecond” timing tool at SLAC’s Linac Coherent Light Source X-ray laser. The dashed line, produced by an algorithm that analyzes the colorized spectrograph image (bottom) represents the arrival time of the X-ray laser. (Ryan Coffee and Nick Hartmann/SLAC)

    Timing tools now in place at most LCLS experimental stations can measure the arrival time of the optical and X-ray laser pulses to an accuracy within 10 femtoseconds, or quadrillionths of a second. The new pulse-measuring system, which is highlighted in the July 27 edition of Nature Photonics, builds upon the existing tools and pushes timing to attoseconds, which are quintillionths (billion-billionths) of a second.

    anime
    This animation shows a sequence of spectrograph images used to precisely measure arrival time of X-rays relative to optical laser pulses at SLAC’s LCLS. The upper edge of the dark blue pattern represents the arrival time of the X-ray laser pulse. The scale at left measures the relative delay of X-ray and optical laser pulses, and the bottom measures the wavelength of the transmitted optical light. (Nick Hartmann/SLAC)

    Nick Hartmann, an LCLS research associate and doctoral student at the University of Bern in Switzerland who is the lead author of the study detailing the system, said, “An X-ray laser with attosecond timing resolution would open up a new class of experiments on the natural time scale of electron motion.”

    The new system uses a high-resolution spectrograph, a type of camera that records the timing and wavelength of the probe laser pulses. The colorful patterns it displays represent the different wavelengths of light that passed, at slightly different times, through a thin sample of silicon nitride.

    This material experiences a cascading reaction in its electrons when it is struck by an X-ray pulse. This effect leaves a brief imprint in the way light passes through the sample, sort of like a temporary interruption of vision following a camera’s flash.

    This X-ray-caused effect shows up in the way the light from the other laser pulse passes through the silicon nitride – it is seen as a brief dip in the amount of light recorded by the spectrograph, like the after-image of a camera flash. An image-analysis algorithm then precisely calculates, based on the recorded patterns, the relative arrival time of the X-ray pulses.

    The new timing system is designed to avoid distortion effects caused by some other timing tools and to work reliably with a variety of focusing and filtering tools. It can provide real-time readouts of laser arrival times and jitter to benefit experiments in progress, and can be added to existing timing setups at LCLS.

    Hartmann said additional innovations could expand the applications of the new system: “We are putting the parts together to allow attosecond experiments at LCLS and other X-ray lasers like it.”

    three
    hese three panels show different types of jitter, or fluctuations, in the X-ray laser pulses produced at SLAC’s Linac Coherent Light Source. The left panel shows how the X-ray beam fluctuates in its direction. The middle panel shows how the spectrum (wavelength or “color”) of the X-ray laser changes randomly from pulse to pulse. The right panel shows the X-ray-caused dip in the amount of light being recorded. (SLAC)

    See the full article here.

    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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  • richardmitnick 7:36 pm on July 22, 2014 Permalink | Reply
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    From SLAC: “Bringing High-energy X-rays into Better Focus” 


    SLAC Lab

    July 22, 2014
    SLAC-invented Etching Process Builds Custom Nanostructures for X-ray Optics

    Scientists at the Department of Energy’s SLAC National Accelerator Laboratory have invented a customizable chemical etching process that can be used to manufacture high-performance focusing devices for the brightest X-ray sources on the planet, as well as to make other nanoscale structures such as biosensors and battery electrodes.

    “The tools researchers use to manipulate X-rays today are very limited,” said Anne Sakdinawat, an associate staff scientist at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL) who developed the new “V-MACE” process with Chieh Chang, an SSRL research associate.

    scan
    Scanning electron microscope image of a cleaved spiral zone plate, a type of X-ray optic, created using a chemical etching technique that was developed at SLAC. (Chieh Chang, Anne Sakdinawat)

    “Our new technique for fabricating high performance X-ray optics involves just a few chemicals in a simple, easy-to-implement, one-step technology,” Sakdinawat said. “It offers significant advantages in many far-ranging applications.” The patent-pending technique is detailed in the June 27 edition of Nature Communications.

    Focusing X-rays, particularly higher-energy or “hard” X-rays, is particularly challenging at the nanoscale, though it is key to the success of many scientific studies at two of SLAC’s DOE Office of Science user facilities, SSRL and the Linac Coherent Light Source (LCLS) X-ray laser.

    It is also of great interest for commercial applications such as X-ray microscopy, complex electronics, and biomedical devices and imaging tools.

    Existing tools for focusing hard X-rays, such as specialized mirrors and sequences of concave metal structures that form lenses, are generally limited in how they can shape the X-ray light. Focusing the highest-energy X-rays to produce crisp images remains a challenge, as the focusing tools themselves generally lack nanoscale precision and sap away much of the X-ray energy.

    “It’s been technologically very difficult to fabricate structures that offer both high resolution and high efficiency,” Sakdinawat said, and the effectiveness of the structures, which are examples of X-ray “diffractive optics,” is typically based on the height and precision of their features.

    The new fabrication technique is adapted from a process used to create hairlike silicon wires for research on advanced batteries and electronics. It can fabricate structures up to 100 times as tall as they are wide, with dimensions accurate to billionths of a meter. The technique reduces the need to stack multiple layers to create tall structures.

    The researchers used the etching technique to build tall, precise X-ray diffractive optics, called zone plates, whose thinly spaced lines, symmetric rings or spiral patterns alternately obstruct or phase-shift X-rays and allow them to pass through in a way that separates and refocuses them. This improves the focus and produces higher-quality images.

    zone
    Scanning electron microscope (SEM) image of a zone plate pattern produced using a chemical etching technique invented at SLAC. (Chieh Chang, Anne Sakdinawat)

    zone2
    This scanning electron microscope image shows a cross-sectional view of a zone plate produced using a patent-pending chemical etching technique called “V-MACE” developed at SLAC. (Chieh Chang, Anne Sakdinawat)

    “Basically, this is like an artificial crystal,” Sakdinawat said, diffracting the X-ray light in a predictable pattern, as a crystal would. “You can basically manipulate the light in whatever fashion you want – you can shape the light in different ways,” she said, based on the design of the optics and the needs of the experiment.

    Sakdinawat and Chang tested and imaged a sample zone plate at SSRL, and they hope to construct similar plates for use in experiments at SSRL and LCLS.

    The same technique can be used to build other types of precise silicon and metal-coated nanostructures, such as filtration devices, thermoelectric devices that can create electricity from heat and components for tiny bio-sensors that can be embedded in the body, and researchers are working to tailor the process to suit the needs of government agencies and corporate partners.

    “We’re trying to expand into other fields,” Sakdinawat said. “There are many different applications for this.”

    See the full article here.

    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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  • richardmitnick 8:06 pm on July 17, 2014 Permalink | Reply
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    From SLAC Lab: “X-ray Laser Measures Leaping Electrons” 


    SLAC Lab

    July 17, 2014
    SLAC Experiment Provides New Insight About How Electrons Move Across Molecules

    Many chemical reactions – such as those at work in batteries and photosynthesis – rely on electrons moving from one atom or molecule to another. Now, scientists have directly measured the movement of electrons as they leap across parts of the same molecule, which provides useful insight about the mechanisms involved in forming and breaking chemical bonds.

    The experiment took place at SLAC’s Linac Coherent Light Source (LCLS) X-ray laser, a DOE Office of Science user facility. Scientists split molecules with pulses of infrared light and then hit them with intense X-ray pulses to drive and study the transfer of electrons between the fragments. The experiment showed that the electrons can travel surprisingly long distances – up to 10 times the length of the original, intact molecule – to jump the gap. The results are published in the July 18 issue of Science.

    “This is a clean example of a very important charge-transfer process that can only be resolved using a tool like LCLS,” said Artem Rudenko of Kansas State University, who led the experiment. The knowledge gained in the experiment may ultimately help to explain mechanisms of electron transfer in more complex molecules, including biological samples. This is also central to understanding how X-rays can damage samples and obscure X-ray images.

    As a basic form of chemical reaction, electron transfer is vital to many life processes. The 1992 Nobel Prize in Chemistry recognized pioneering theoretical work in electron transfer that has underpinned many related chemistry experiments.

    The team studied methyl iodide molecules, also known as iodomethane, which break in a predictable way when hit by intense infrared light: One fragment contains a single iodine atom, the other has carbon and hydrogen atoms.

    iodide
    In this illustration of a severed methyl iodide molecule, electrons jump the gap from one fragment containing carbon and hydrogen atoms (right) to the other fragment, which contains an iodine atom (left). Researchers used SLAC’s Linac Coherent Light Source X-ray laser to stimulate and measure the electron-transfer process. (SLAC National Accelerator Laboratory) “>In this illustration of a severed methyl iodide molecule, electrons jump the gap from one fragment containing carbon and hydrogen atoms (right) to the other fragment, which contains an iodine atom (left). Researchers used SLAC’s Linac Coherent Light Source X-ray laser to stimulate and measure the electron-transfer process. (SLAC National Accelerator Laboratory)

    They tuned the LCLS X-ray pulses to knock out electrons only from the iodine atoms, creating a positive charge that attracts electrons from the other fragment to fill the vacancies. As the fragments drift, the gap that electrons jump to reach the iodine atoms widens until it becomes too far for them to reach.

    The researchers varied the timing of the X-ray pulses to tune the distance electrons had to jump to cross this gap. They used time- and position-sensitive detectors to determine the final charge and energy of the fragments, which told them where the remaining electrons ended up. While LCLS X-ray laser pulses are ultrashort, lasting just quadrillionths of a second, or femtoseconds, the electron-transfer process typically spans less than a single femtosecond, Rudenko noted. During this very short time, the distance between the fragments does not change, allowing researchers to more easily gauge the electron movement.

    “With each pair of infrared and X-ray pulses we tried to look at just one molecule,” said Benjamin Erk of Germany’s DESY lab, who analyzed the data. “We traced essentially all of the fragments produced to give us a microscopic ‘picture’ of a single fracture event.” Researchers collected data from about 800,000 fractured molecules.

    The same team, which was also led by Daniel Rolles of DESY, has already conducted follow-up research on other molecules at LCLS, and researchers said it may be possible to study biological compounds found in DNA and RNA, as an example, using the same method. They hope to directly measure the time it takes for the electrons to move across larger and more complex molecules, Rudenko said.

    In addition to researchers from Kansas State University, DESY and SLAC, other collaborating researchers were from the Center for Free-Electron Laser Science, Max Planck Institute for Nuclear Physics, Max Planck Institute for Medical Research, University of Hamburg and Physikalisch-Technische Bundesanstalt (National Metrology Institute), all in Germany; and from Sorbonne University and the French National Center for Scientific Research in France.

    The work was supported by the Max Planck Society, which funded the development and operation of the CAMP instrument used in the experiment; the U.S. Department of Energy Office of Science; the Kansas NSF EPSCoR “First Award” program; the Young Investigator Program of the Helmholtz Association; and the German Research Foundation’s Hamburg Center for Ultrafast Imaging – Structure, Dynamics and Control of Matter at the Atomic Scale.

    See the full article here.

    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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  • richardmitnick 2:12 pm on June 27, 2014 Permalink | Reply
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    From SLAC lab: “X-ray Laser Gives Buckyballs a Big Kick” 


    SLAC Lab

    June 27, 2014
    Glenn Roberts Jr.

    Scientists at SLAC have been blowing up “buckyballs” – soccer-ball-shaped carbon molecules – with an X-ray laser to understand how they fly apart. The results, they say, will aid biological studies by improving the analysis of X-ray images of tiny viruses, individual proteins and other important biomolecules.

    bb
    Buckyball shape

    The experiment was carried out at SLAC’s Linac Coherent Light Source (LCLS) X-ray laser, a DOE Office of Science user facility, and the results appear in the June 27 issue of Nature Communications.

    “It’s sort of a Catch-22: You need the X-ray laser focus to be extremely intense and bright to get a good picture,” says Nora Berrah, an experimental physicist at the University of Connecticut. “But the X-rays also trigger unexpectedly rapid and substantial damage and motion in the atoms, resulting in a blurred image.” Berrah led the research with Robin Santra, a theorist from the Center for Free-Electron Laser Science at Germany’s DESY lab.

    Because buckyballs are composed entirely of carbon – the backbone of all life on Earth – they are a good stand-in for biological molecules, many of which also have strong atomic bonds. They got their formal name, “buckminsterfullerene,” for their resemblance to the geodesic domes invented by R. Buckminster Fuller.

    Within 20 femtoseconds, or quadrillionths of a second, after being struck by LCLS X-rays, atoms in the buckyballs had flown apart and traveled a distance about 10 times longer than their own diameters, the researchers reported.

    “The bright X-rays knock a large number of electrons out of the molecule, its atoms become more and more positively charged, and the electric repulsion finally lets the molecule explode,” Berrah said.

    Just as fast-moving objects can blur conventional photographs, the high speeds of atoms and free-floating electrons in an exploding molecule can obscure X-ray images, so the best way to observe a molecule in its intact state is to use the shortest, brightest pulses available at LCLS to snap images before any damage occurs.

    In addition, modeling the details of the damage can help researchers find the best timing and techniques for capturing accurate images that map the 3-D structure and other properties of the samples.

    At LCLS, researchers used a specialized oven to create a thin gas beam of buckyballs that passed into the path of LCLS X-ray pulses. They varied the energy and length of the LCLS pulses and used a specialized spectrometer, developed in Sweden, to measure charged fragments of the molecules in the X-ray-driven explosions and their aftermath.

    On average, about 180 particles of light, called photons, entered each buckyball struck by an LCLS pulse, and in some cases they stripped all the electrons from the carbon atoms while blowing the molecule apart.

    Then the highly charged buckyball bits, known as ions, formed tiny plasmas and began to pull free-floating electrons back toward them – a process known as “secondary ionization.”

    Without experiments, developing models that simulate and predict the behavior of large, complex molecules is challenging even with powerful computers, Berrah noted. The experiment at LCLS was key in helping to construct and validate a new theoretical model to explain how buckyballs behave under extreme X-ray intensity.

    “What’s most important, in fact, are the secondary ionization effects that were explained by the model, which we validated,” Berrah explained. “These effects were stronger and lasted longer than expected.”

    The scientists compared the debris of the molecular explosion with a simulation developed by DESY scientist Zoltan Jurek of CFEL. “Such simulation tools were originally developed for things like liquids and polymers that are at or near equilibrium, not for the high energies and strong forces we see here,” explains Jurek. “Nobody knew if this would really work.”

    Berrah said, “We needed the experimental data to build and develop the model. At the same time, this powerful model allowed us to interpret the data. This is an important milestone for the investigation of individual, complex biomolecules like proteins with lasers like LCLS.”

    In addition to the University of Connecticut, the Center for Free-Electron Laser Science and SLAC, other collaborators in the study are from Western Michigan University, The Hamburg Center for Ultrafast Imaging and University of Hamburg in Germany, University of Gothenburg in Sweden, Oxford University in the United Kingdom, the Institute of Inorganic Methodologies and Plasmas in Italy, Stanford PULSE Institute, Imperial College London, University of Turku in Finland, University of Texas at Austin, Synchrotron SOLEIL in France and Tohoku University in Japan.

    This work was supported by the DOE Office of Science, the Hamburg Center for Ultrafast Imaging in Germany, the Swedish Research Council, Göran Gustafsson and Knut and Alice Wallenberg foundations in Sweden, and the Engineering and Physical Sciences Research Council in the U.K.

    See the full article here.

    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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  • richardmitnick 4:42 pm on May 1, 2014 Permalink | Reply
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    From SLAC Lab: “Revealed at Last: Atomic Mechanism for Historic Materials Transformation” 


    SLAC Lab

    May 1, 2014
    Mike Ross

    SLAC-led researchers have made the first direct measurements of a small and extremely rapid atomic rearrangement, associated with a class called martensitic transformations, that dramatically changes the properties of many important materials, such as doubling the hardness of steel and causing shape-memory alloys to revert to a previous shape.

    nano
    This graphic depicts the transformation of cadmium sulfide nanocrystals from a hexagonal arrangement (left) to a cubic one (right). A slightly compressed intermediate state that SLAC-led researchers saw is portrayed in the middle. (Greg Stewart/SLAC)

    Using high-pressure shock waves and ultrashort X-ray pulses at the Linac Coherent Light Source (LCLS), the researchers observed the details of how this transformation changed the internal atomic structure of a model system, perfect nanocrystals of cadmium sulfide. In the process, they saw for the first time that the nanocrystals pass through a theoretically-predicted intermediate state when undergoing this change.

    “To design and engineer new materials with desired properties, we would like to understand the detailed microscopic pathways they follow as they transform,” said the team’s leader, Aaron Lindenberg, an assistant professor at SLAC and Stanford. “The martensitic transformation is especially important since it occurs in so many important materials. Our technique should ultimately help us see what’s happening in other atomic transformations as well.”

    lines
    A composite of about 300 stop-action X-ray diffraction images shows the martensitic transformation of cadmium sulfide nanocrystals. Looking from left to right, the light blue line at the top comes from the hexagonal atomic arrangement. It disappears about 250 picoseconds (trillionths of a second) after the beginning of the experiment and is replaced about 50 picoseconds later (to the right) by the signature of the cubic form: a bright blue line above the dark red line on the right side of the image. (Joshua Wittenberg/SLAC and Stanford)

    The team’s research results were published last month in Nano Letters.

    Named after pioneering German metallurgist Adolf Martens, the martensitic transformation involves collective short-range movements of the atoms in a crystalline solid as it responds to stress. It has been studied for more than 100 years after Martens and colleagues identified that an altered crystalline form in rapidly cooled high-carbon steel was responsible for its enhanced hardness. While the actual atomic movements in martensitic transformations are typically smaller than a nanometer, they can have huge effects on a material’s properties. In addition to hardening steel and facilitating shape-memory alloys, the martensitic transformation underlies such diverse phenomena as geological deformation due to plate tectonics and the mechanism by which invading viruses puncture the walls of cells.

    They hit a metal foil with an intense infrared laser pulse, causing it to explode and send a high-pressure shock crashing through the nanocrystals. Pressure from the passing shock wave initiated the transformation. The LCLS X-ray pulses were timed to hit the sample at various split-second times after the shock, producing stop-action X-ray diffraction images that showed the precise positions of the nanocrystal’s atoms during various stages of the transformation, which took only 50 trillionths of a second to complete. The scientists also varied the laser intensity to create shocks of different peak pressures.

    The team found that the transformations caused by the higher-pressure shocks proceeded directly from hexagonal to cubic, while those triggered by the lower-pressure shocks formed a temporary intermediate state. Calculated simulations by other researchers had predicted the intermediate, Lindenberg said. But its absence in the high-pressure case may be an indication that strong shocks act like catalysts, lowering the energy barrier of the transformation so it can proceed directly.

    “This set of experiments shows the power of using LCLS, high-power lasers and nanocrystals to examine the rapid atomic rearrangements that are so important in creating materials properties,” Lindenberg said. “Until now, there have only been theoretical calculations of how these transformations should occur. Now we can learn firsthand what really happens.”

    This research was conducted at the X-ray Pump Probe (XPP) experimental station at LCLS. Additional collaborators included researchers from the University of California, Berkeley; Argonne National Laboratory in Illinois; and the University of Duisburg-Essen in Germany. The researchers acknowledge funding from the DOE Office of Science and the German Research Council.

    See the full article here.

    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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