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  • richardmitnick 10:42 am on June 15, 2019 Permalink | Reply
    Tags: A tale of two liquids, , , , , , SLAC LCLS, When stable becomes unstable,   

    From SLAC National Accelerator Lab: “A quick liquid flip helps explain how morphing materials store information” 

    From SLAC National Accelerator Lab

    June 14, 2019

    Experiments at SLAC’s X-ray laser reveal in atomic detail how two distinct liquid phases in these materials enable fast switching between glassy and crystalline states that represent 0s and 1s in memory devices.

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    In phase-change memory devices, a material switches between glassy and crystalline phases that represent the 0s and 1s used to store information. One pulse of electricity or light heats the material to high temperature, causing it to crystallize, and another pulse melts it into a disordered, glassy state. Experiments at SLAC’s X-ray laser revealed a key part of this switch – a quick transition from one liquid-like state to another – that enables fast and reliable data storage. (Peter Zalden/European XFEL)

    Instead of flash drives, the latest generation of smart phones uses materials that change physical states, or phases, to store and retrieve data faster, in less space and with more energy efficiency. When hit with a pulse of electricity or optical light, these materials switch between glassy and crystalline states that represent the 0s and 1s of the binary code used to store information.

    Now scientists have discovered how those phase changes occur on an atomic level.

    Researchers from European XFEL and the University of Duisburg-Essen in Germany, working in collaboration with researchers at the Department of Energy’s SLAC National Accelerator Laboratory, led X-ray laser experiments at SLAC that collected more than 10,000 snapshots of phase-change materials transforming from a glassy to a crystalline state in real time.

    They discovered that just before the material crystallizes, it changes from one liquid-like state to another, a process that could not be clearly seen in prior studies because it was blurred by the rapid motions of the atoms. And they showed that this transition is responsible for the material’s unique ability to store information for long periods of time while also quickly switching between states.

    The results, published in Science today, offer a new strategy for designing improved phase-change materials for specialized memory storage.

    “Current data storage technology has reached a scaling limit, so that new concepts are required to store the amounts of data that we will produce in the future,” said Peter Zalden, a scientist at European XFEL and lead author of the study. “Our study explains how the switching process in a promising new technology can be fast and reliable at the same time.”

    When stable becomes unstable

    The experiments took place at SLAC’s Linac Coherent Light Source (LCLS) which produces X-ray laser pulses that are short enough and intense enough to capture snapshots of atomic changes occurring in femtoseconds – millionths of a billionths of a second.

    To store information with phase-change materials, they must be cooled quickly to enter a glassy state without crystallizing, and remain in this glassy state as long as the information needs to stay there. This means the crystallization process must be very slow to the point of being almost absent, such as is the case in ordinary glass. But when it comes time to erase the information, which is done by applying high temperatures, the same material has to crystallize very quickly. The fact that a material can form a stable glass but then become very unstable at elevated temperatures has puzzled researchers for decades.

    At LCLS, the scientists used an optical laser to rapidly heat amorphous films of phase-change materials, just 50 nanometers thick, atop an equally thin support. The films cooled into a crystalline state as the heat from the laser blast dissipated into the surrounding support structure over billionths of a second.

    They used X-ray laser pulses to make images of the material’s structural evolution, collecting each snapshot in the instant before a sample deteriorated.

    A tale of two liquids

    The researchers found that when the liquid cools far enough below the material’s melting temperature, it undergoes a structural change to form another, lower-temperature liquid that exists for just billionths of a second.

    The two liquids not only have very different atomic structures, but they also behave differently: The one at higher temperature has highly mobile atoms that can quickly arrange themselves into the well-ordered structure of a crystal. But in the lower-temperature liquid, some chemical bonds become stronger and more rigid and can hold the disordered atomic structure of the glass in place. It is only the rigid nature of these chemical bonds that keeps the glass from crystallizing and – in the case of phase-change memory devices – secures information in place. The results also help scientists understand how other classes of materials form a glass.

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    The research team after performing experiments at SLAC’s Linac Coherent Light Source X-ray laser. (Klaus Sokolowski-Tinten/University of Duisburg-Essen)

    See the full article here.
    See the XFEL press release here .


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    Please help promote STEM in your local schools.

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    SLAC/LCLS


    SLAC/LCLS II projected view


    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.

     
  • richardmitnick 9:11 am on April 25, 2019 Permalink | Reply
    Tags: "Researchers create the first maps of two melatonin receptors essential for sleep", , , Melatonin receptors belong to a group of membrane receptors called G protein-coupled receptors (GPCRs) which regulate almost all the physiological and sensory processes in the human body., MT1 and MT2 receptors, SLAC LCLS, These receptors oversee our clock genes- the timekeepers of the body’s internal clock or circadian rhythm., University of Southern California, When our circadian rhythms are disrupted it can lead to a number of downstream symptoms increasing the risk of cancer Type 2 diabetes and mood disorders., When there’s light the production of melatonin is inhibited; but when darkness comes that's the signal for our brains to go to sleep.,   

    From SLAC National Accelerator Lab: “Researchers create the first maps of two melatonin receptors essential for sleep” 

    From SLAC National Accelerator Lab

    April 24, 2019

    Andrew Gordon
    agordon@slac.stanford.edu
    (650) 926-2282

    Written by Ali Sundermier

    1
    The behavior of humans and all animals is governed by a variety of natural cycles. The shift of seasons, tides, and day and night influences animal breeding and mating, predator-prey relationships, migration and foraging. Melatonin, depicted as a constellation in the night sky, is the key molecule that allows one of the most stable of these external cycles, a 24-hour day-night rhythm, to be correlated to an internal cycle, with responses at the level of individual cells and the whole animal. High melatonin levels during night time induce sleep-promoting properties by acting through melatonin receptors, depicted in the central reference point of the image composition. (Yekaterina Kadyshevskaya/Bridge Institute of the University of Southern California)

    A better understanding of how these receptors work could enable scientists to design better therapeutics for sleep disorders, cancer and Type 2 diabetes.

    An international team of researchers used an X-ray laser at the Department of Energy’s SLAC National Accelerator Laboratory to create the first detailed maps of two melatonin receptors that tell our bodies when to go to sleep or wake up, and guide other biological processes. A better understanding of how they work could enable researchers to design better drugs to combat sleep disorders, cancer and Type 2 diabetes. Their findings were published in two papers today in Nature: Structural basis of ligand recognition at the human MT1 melatonin receptor; XFEL structures of the human MT2 melatonin receptor reveal the basis of subtype selectivity.

    The team, led by the University of Southern California, used X-rays from SLAC’s Linac Coherent Light Source (LCLS) to map the receptors, MT1 and MT2, bound to four different compounds that activate them: an insomnia drug, a drug that mixes melatonin with the antidepressant serotonin, and two melatonin analogs.

    SLAC/LCLS

    They discovered that both melatonin receptors contain narrow channels embedded in the fatty membranes of the cells in our bodies. These channels only allow melatonin – which can exist in both water and fat – to pass through and bind to the receptors, blocking serotonin, which has a similar structure but is only happy in watery environments. They also uncovered how some much larger compounds may only target MT1 and not MT2, despite the structural similarities between the two receptors. This should inform the design of drugs that selectively target MT1, which so far has been challenging.

    “These receptors perform immensely important functions in the human body and are major drug targets of high interest to the pharmaceutical industry,” said Linda Johansson, a postdoctoral scholar at USC who led the structural work on MT2. “Through this work we were able to obtain a highly detailed understanding of how melatonin is able to bind to these receptors.”

    Time for bed

    People do it, birds do it, fish do it. Almost all living beings in the animal kingdom sleep, and for good reason.

    “It’s critical for the brain to take rest and process and store memories that we have accumulated during the day,” said co-author Alex Batyuk, a scientist at SLAC. “Melatonin is the hormone that regulates our sleep-wake cycles. When there’s light, the production of melatonin is inhibited, but when darkness comes that’s the signal for our brains to go to sleep.”

    Melatonin receptors belong to a group of membrane receptors called G protein-coupled receptors (GPCRs) which regulate almost all the physiological and sensory processes in the human body. MT1 and MT2 are found in many places throughout the body, including the brain, retina, cardiovascular system, liver, kidney, spleen and intestine.

    These receptors oversee our clock genes, the timekeepers of the body’s internal clock, or circadian rhythm. In a perfect world, our internal clocks would sync up with the rising and setting of the sun. But when people travel across time zones, work overnight shifts or spend too much time in front of screens or other artificial sources of blue light, these timekeepers are thrown out of whack.

    Controlling the rhythm

    When our circadian rhythms are disrupted, it can lead to a number of downstream symptoms, increasing the risk of cancer, Type 2 diabetes and mood disorders. MT1 in particular plays an important role in controlling these rhythms but designing drugs that can selectively target this receptor has proven difficult. Many people take over-the-counter melatonin supplements to combat sleep issues or shift their circadian rhythms, but these drugs often wear off within hours and can produce unwanted side effects.

    By cracking the blueprints of these receptors and mapping how ligands bind to and activate them, the researchers lit the way for others to design drugs that are safer, more effective and capable of selectively targeting each receptor.

    “Since the discovery of melatonin 60 years ago, there have been many landmark discoveries that led to this moment,” said Margarita L. Dubocovich, a State University of New York Distinguished Professor of pharmacology and toxicology at the University at Buffalo who pioneered the identification of functional melatonin receptors in the early 80s and provided an outside perspective on this research. “Despite remarkable progress, discovery of selective MT1 drugs has remained elusive for my team and researchers around the world. The elucidation of the crystal structures for the MT1 and MT2 receptors opens up an exciting new chapter for the development of drugs to treat sleep or circadian rhythm disorders known to cause psychiatric, metabolic, oncological and many other conditions.”

    Harvesting crystals

    To map biomolecules like proteins, researchers often use a method called X-ray crystallography, scattering X-rays off of crystallized versions of these proteins and using the patterns this creates to obtain a three-dimensional structure. Until now, the challenge with mapping MT1, MT2 and similar receptors was how difficult it was to grow large enough crystals to obtain high-resolution structures.

    “With these melatonin receptors, we really had to go the extra mile,” said Benjamin Stauch, a scientist at USC who led the structural work on MT1. “Many people had tried to crystallize them without success, so we had to be a little bit inventive.”

    A key piece of this research was the unique method the researchers used to grow their crystals and to collect X-ray diffraction data from them. For this research, the team expressed these receptors in insect cells and extracted them by using detergent. They mutated these receptors to stabilize them, enabling crystallization. After purifying the receptors, they placed them in a membrane-like gel, which supports crystal growth directly from the membrane environment. After obtaining microcrystals suspended in this gel, they used a special injector to create a narrow stream of crystals that they zapped with X-rays from LCLS.

    “Because of the tiny crystal size, this work could only be done at LCLS,” said Vadim Cherezov, a USC professor who supervised both studies. “Such small crystals do not diffract well at synchrotron sources as they quickly suffer from radiation damage. X-ray lasers can overcome the radiation damage problem through the ‘diffraction-before-destruction’ principle.”

    The researchers collected hundreds of thousands of images of the scattered X-rays to figure out the three-dimensional structure of these receptors. They also tested the effects of dozens of mutations to deepen their understanding of how the receptors work.

    3
    The researchers showed that both melatonin receptors contain narrow channels embedded in the cell’s fatty membranes. These channels only allow melatonin, which can exist happily in both water and fat, to pass through, preventing serotonin, which has a similar structure but is only happy in watery environments, from binding to the receptor. They also uncovered how some much larger compounds only target MT1 despite the structural similarities between the two receptors. (Greg Stewart/SLAC National Accelerator Laboratory)

    In addition to discovering tiny, gatekeeping melatonin channels in the receptors, the researchers were able to map Type 2 diabetes-associated mutations onto the MT2 receptor, for the first time seeing the exact location of these mutations in the receptor.

    Laying the groundwork

    In these experiments, the researchers only looked at compounds that activate the receptors, known as agonists. To follow up, they hope to map the receptors bound to antagonists, which block the receptors. They also hope to use their techniques to investigate other GPCR receptors in the body.

    “As a structural biologist, it was exciting to see the structure of these receptors for the first time and analyze them to understand how these receptors selectively recognize their signaling molecules,” Cherezov said. “We’ve known about them for decades but until now no one could say how they actually look. Now we can analyze them to understand how they recognize specific molecules, which we hope lays the groundwork for better, more effective drugs.”

    The team also included researchers from the University of North Carolina at Chapel Hill; Stanford University; Arizona State University; the University of Lille in France; and the University at Buffalo. LCLS is a DOE Office of Science user facility. This research was largely supported by the National Institutes of Health and the National Science Foundation BioXFEL Science and Technology Center.

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    SLAC/LCLS


    SLAC/LCLS II projected view


    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.

     
  • richardmitnick 8:29 am on April 23, 2019 Permalink | Reply
    Tags: "A day in the life of a midnight beam master", , , Ben Ripman- operations engineer at the SLAC accelerator control room, , SLAC LCLS, SLAC SPEAR3, ,   

    From SLAC National Accelerator Lab: “A day in the life of a midnight beam master” 

    From SLAC National Accelerator Lab

    April 16, 2019 [Just today 4.23.19 in social media]
    Angela Anderson

    In SLAC’s accelerator control room, shift lead Ben Ripman and a team of operators fine-tune X-ray beams for science experiments around the clock.

    When is a day not a day? When you work in the central nervous system of the world’s longest linear accelerator, open 24-7.

    “There’s a constant cycle of people coming and going,” says Ben Ripman, an operations engineer at the Department of Energy’s SLAC National Accelerator Laboratory.

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    Ben Ripman, operations engineer at the SLAC accelerator control room (Angela Anderson/SLAC National Accelerator Laboratory)

    He might start at 8 a.m., at 4 p.m. or at midnight. But the shift rotations are no barrier to his passion for the job – leading a team of control room operators who deliver brilliant X-ray beams for scientific experiments.

    Control room operators spend most of their workdays (or nights) in a room filled with monitors, three deep and crowded with numbers, charts and graphs. Those displays track the status of thousands of devices and systems in the linear accelerator that runs through a tunnel below Highway 280 and feeds SLAC’s X-ray laser, the Linac Coherent Light Source (LCLS).

    SLAC/LCLS

    The accelerator boosts electrons to almost the speed of light and then wiggles them between magnets to generate X-rays. That X-ray light is formed into pulses and optimized for materials science, biology, chemistry, and physics experiments.

    The entire operation is monitored in the control room, which also serves SPEAR3, the accelerator that produces X-rays for the Stanford Synchrotron Radiation Lightsource (SSRL).

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    SLAC SPEAR3

    SLAC/SSRL

    Another set of monitors, staffed by SLAC Facilities, tracks water, compressed air and electricity systems that serve the lab campus.

    Ripman and his fellow operators are experts in reading these digital vital signs. But they are also some of the most knowledgeable people at the lab when it comes to the entire physical machine.

    “We know the accelerator from beginning to end,” he says. “When an operator adjusts something from the control room, they can picture that machine part and what it is doing.”

    For LCLS, they measure the amount of energy in individual X-ray pulses being fed to experimental hutches and often spend hours improving the pulses: tweaking magnets, adjusting the undulators, tuning the shape and length of the electron bunches.

    Some days the control room is quiet, and the operators focus on training and individual projects. On other, more challenging days when the machine is running in exotic modes, they work elbow to elbow with physicists.

    “We love this machine, but the accelerator was built decades ago and can be cantankerous,” Ripman explains. “When things do go wrong, it’s like a game of pickup sticks – one problem triggers another and you need to know how it all fits together.”

    An important part of the job is knowing who to call for help. “We wake up a lot of people in the middle of the night,” Ripman says with a smile.

    Control room operators also make sure everyone who goes into the accelerator tunnel stays safe.

    There are two ways to get into the accelerator. For minor repairs and inspections, people take keys from special key banks that block the accelerator from turning on until all the keys have been returned. On official maintenance days, the doors are thrown open.

    “On those days, maintenance crews, engineers and physicists descend into the tunnel and swarm the machine to resolve as many issues as possible before we have to summon them out again,” Ripman says. “We search the machine to make sure everyone is out before it’s turned back on.”

    Almost all of the displays in the control room were designed by the operators, he says. “We are known to hide ‘Easter eggs’ in them, but you have to get in our good graces to find out about them.”

    New operators take more than a year to get trained and proficient, Ripman says. “People come with a physics degree, but there is not a lot of formal coursework you can take on accelerator operations – it’s a lot of on-the-job training.”

    It was that hands-on learning that drew him to the job in 2010.

    “I was a nerd in high school,” Ripman admits proudly, “Stephen Hawking was my hero.” After studying physics and astronomy in college, Ripman worked as a contractor for NASA before joining SLAC. On his off hours, he plays board games and travels several times a year for card tournaments. He also loves hiking, skiing and snowboarding, and is a member of the Stanford University Singers.

    His favorite thing about the job? “My coworkers,” he says. “I have the privilege of working with smart, fun, quirky people. We all get along quite well, and there’s a great camaraderie.”

    Operators leave sticky notes with jokes or short messages for the next shift and share stories about their days and nights in the accelerator’s brain.

    Like the one about a ghost calling from an abandoned tunnel. But that’s a tale for another night…

    LCLS and SSRL are DOE Office of Science user facilities.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    SLAC/LCLS


    SLAC/LCLS II projected view


    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.

     
  • richardmitnick 11:18 am on April 15, 2019 Permalink | Reply
    Tags: "SLAC’s high-speed ‘electron camera’ films molecular movie in HD", , , , , How a bond in the ring breaks and atoms jiggle around for extended periods of time., , Researchers have made the first high-definition “movie” of ring-shaped molecules breaking open in response to light, SLAC LCLS, , The results demonstrate how our unique instruments for studying ultrafast processes complement each other, This allows us to ask new questions about fundamental processes stimulated by light., UED-ultrafast electron diffraction instrument   

    From SLAC National Accelerator Lab: “SLAC’s high-speed ‘electron camera’ films molecular movie in HD” 

    From SLAC National Accelerator Lab

    April 15, 2019

    Manuel Gnida
    mgnida@slac.stanford.edu
    (650) 926-2632

    1
    This illustration shows snapshots of the light-triggered transition of the ring-shaped 1,3-cyclohexadiene (CHD) molecule (background) to its stretched-out 1,3,5-hexatriene (HT) form (foreground). The snapshots were taken with SLAC’s high-speed “electron camera” – an instrument for ultrafast electron diffraction (UED). (Greg Stewart/SLAC National Accelerator Laboratory)

    With an extremely fast “electron camera” at the Department of Energy’s SLAC National Accelerator Laboratory, researchers have made the first high-definition “movie” of ring-shaped molecules breaking open in response to light. The results could further our understanding of similar reactions with vital roles in chemistry, such as the production of vitamin D in our bodies.


    Visualization of a molecular movie made with SLAC’s electron camera, in which researchers have captured in atomic detail how a ring-shaped molecule opens up in the first 800 millionths of a billionth of a second after being hit by a laser flash. Ring-opening reactions like this one play important roles in chemistry, such as the light-driven synthesis of vitamin D in our bodies. (Thomas Wolf/PULSE Institute)

    A previous molecular movie of the same reaction, produced with SLAC’s Linac Coherent Light Source (LCLS) X-ray laser, for the first time recorded the large structural changes during the reaction.


    This video describes how the Linac Coherent Light Source, an X-ray free-electron laser at SLAC National Accelerator Laboratory, provided the first direct measurements of how a ring-shaped gas molecule unravels in the millionths of a billionth of a second after it is split open by light. The measurements were compiled in sequence to form the basis for computer animations showing molecular motion. (SLAC National Accelerator Laboratory)

    Now, making use of the lab’s ultrafast electron diffraction (UED) instrument, these new results provide high-resolution details – showing, for instance, how a bond in the ring breaks and atoms jiggle around for extended periods of time.

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    August 5, 2015- With SLAC’s new apparatus for ultrafast electron diffraction – one of the world’s fastest “electron cameras” – researchers can study motions in materials that take place in less than 100 quadrillionths of a second. A pulsed electron beam is created by shining laser pulses on a metal photocathode. The beam gets accelerated by a radiofrequency field and focused by a magnetic lens. Then it travels through a sample and scatters off the sample’s atomic nuclei and electrons, creating a diffraction image on a detector. Changes in these diffraction images over time are used to reconstruct ultrafast motions of the sample’s interior structure. (SLAC National Accelerator Laboratory)

    “The details of this ring-opening reaction have now been settled,” said Thomas Wolf, a scientist at the Stanford Pulse Institute of SLAC and Stanford University and leader of the research team. “The fact that we can now directly measure changes in bond distances during chemical reactions allows us to ask new questions about fundamental processes stimulated by light.”

    SLAC scientist Mike Minitti, who was involved in both studies, said, “The results demonstrate how our unique instruments for studying ultrafast processes complement each other. Where LCLS excels in capturing snapshots with extremely fast shutter speeds of only a few femtoseconds, or millionths of a billionth of a second, UED cranks up the spatial resolution of these snapshots. This is a great result, and the studies validate one another’s findings, which is important when making use of entirely new measurement tools.”

    LCLS Director Mike Dunne said, “We’re now making SLAC’s UED instrument available to the broad scientific community, in addition to enhancing the extraordinary capabilities of LCLS by doubling its energy reach and transforming its repetition rate. The combination of both tools uniquely positions us to enable the best possible studies of fundamental processes on ultrasmall and ultrafast scales.”

    The team reported their results today in Nature Chemistry.

    Molecular movie in HD

    This particular reaction has been studied many times before: When a ring-shaped molecule called 1,3-cyclohexadiene (CHD) absorbs light, a bond breaks and the molecule unfolds to form the almost linear molecule known as 1,3,5-hexatriene (HT). The process is a textbook example of ring-opening reactions and serves as a simplified model for studying light-driven processes during vitamin D synthesis.

    In 2015, researchers studied the reaction with LCLS, which resulted in the first detailed molecular movie of its kind and revealed how the molecule changed from a ring to a cigar-like shape after it was struck by a laser flash. The snapshots, which initially had limited spatial resolution, were brought further into focus through computer simulations.

    4
    Researchers created the first atomic-resolution movie of the ring-opening reaction of 1,3-cyclohexadiene (CHD) with an “electron camera” called UED. Bottom: The UED electron beam accurately measures the distances between pairs of atoms in the CHD molecule as the reaction proceeds. The distance between each pair is represented by a colored line in the graph. Variations in the distances as the molecule changes shape represent the molecular movie. Top: Visualization of the molecular structure corresponding to the distance distribution measured at about 380 femtoseconds into the reaction (dashed line at bottom). (David Sanchez/Stanford University)

    The new study used UED – a technique in which researchers send an electron beam with high energy, measured in millions of electronvolts (MeV), through a sample – to precisely measure distances between pairs of atoms.


    Taking snapshots of these distances at different intervals after an initial laser flash and tracking how they change allows scientists to create a stop-motion movie of the light-induced structural changes in the sample.

    The electron beam also produces strong signals for very dilute samples, such as the CHD gas used in the study, said SLAC scientist Xijie Wang, director of the MeV-UED instrument.

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    SLAC Megaelectronvolt Ultrasfast Electron Diffraction Instrument: MeV-UED

    “This allowed us to follow the ring-opening reaction over much longer periods of time than before.”

    Surprising details

    The new data revealed several surprising details about the reaction.

    They showed that the movements of the atoms accelerated as the CHD ring broke, helping the molecules rid themselves of excess energy and accelerating their transition to the stretched-out HT form.

    The movie also captured how the two ends of the HT molecule jiggled around as the molecules became more and more linear. These rotational motions went on for at least a picosecond, or a trillionth of a second.

    “I would have never thought these motions would last that long,” Wolf said. “It demonstrates that the reaction doesn’t end with the ring opening itself and that there is much more long-lasting motion in light-induced processes than previously thought.”

    A method with potential

    The scientists also used their experimental data to validate a newly developed computational approach for including the motions of atomic nuclei in simulations of chemical processes.

    “UED provided us with data that have the high spatial resolution needed to test these methods,” said Stanford chemistry professor and PULSE researcher Todd Martinez, whose group led the computational analysis. “This paper is the most direct test of our methods, and our results are in excellent agreement with the experiment.”

    In addition to advancing the predictive power of computer simulations, the results will help deepen our understanding of life’s fundamental chemical reactions, Wolf said: “We’re very hopeful our method will pave the way for studies of more complex molecules that are even closer to the ones used in life processes.”

    Other research institutions involved in this study were the University of York, UK; University of Nebraska-Lincoln; University of Potsdam, Germany; University of Edinburgh, UK; and Brown University. Large parts of this work were financially supported by the DOE Office of Science. SLAC’s MeV-UED instrument is part of LCLS, a DOE Office of Science user facility.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    SLAC/LCLS


    SLAC/LCLS II projected view


    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.

     
  • richardmitnick 10:05 am on April 4, 2019 Permalink | Reply
    Tags: A new method could turn random fluctuations in the intensity of laser pulses from a nuisance into an advantage facilitating studies of these fundamental interactions., In a computational process that borrows ideas from machine learning researchers can then turn these data into a visualization of the X-ray pulse’s effects on the sample., In addition we need to control the time delay between them very well., Pump-probe experiments therefore typically require that we first prepare well-defined short pulses that are less random, SLAC LCLS, , Taking advantage of X-ray spikes-by repeating the experiment with varying time delays between the pulses researchers can make a stop-motion movie of the tiny fast motions., Taking ghostly snapshots-Daniel Ratner and his coworkers want to apply the technique of ghost imaging., The secret is applying a method known as “ghost imaging” which reconstructs what objects look like without ever directly recording their images., X-ray free-electron lasers (XFELs)   

    From SLAC National Accelerator Lab: “Ghostly X-ray images could provide key info for analyzing X-ray laser experiments” 

    From SLAC National Accelerator Lab

    April 3, 2019
    Manuel Gnida

    1
    SLAC researchers suggest using the randomness of subsequent X-ray pulses from an X-ray laser to study the pulses’ interactions with matter, a method they call pump-probe ghost imaging. (Greg Stewart/SLAC National Accelerator Laboratory)

    X-ray free-electron lasers (XFELs) produce incredibly powerful beams of light that enable unprecedented studies of the ultrafast motions of atoms in matter. To interpret data taken with these extraordinary light sources, researchers need a solid understanding of how the X-ray pulses interact with matter and how those interactions affect measurements.

    Now, computer simulations by scientists from the Department of Energy’s SLAC National Accelerator Laboratory suggest that a new method could turn random fluctuations in the intensity of laser pulses from a nuisance into an advantage, facilitating studies of these fundamental interactions. The secret is applying a method known as “ghost imaging,” which reconstructs what objects look like without ever directly recording their images.

    “Instead of trying to make XFEL pulses less random, which is the approach we most often pursue for our experiments, we actually want to use randomness in this case,” said James Cryan from the Stanford PULSE Institute, a joint institute of Stanford University and SLAC. “Our results show that by doing so, we can get around some of the technical challenges associated with the current method for studying X-ray interactions with matter.”

    The research team published their results in Physical Review X.

    Taking advantage of X-ray spikes

    Scientists commonly look at these interactions through pump-probe experiments, in which they send pairs of X-ray pulses through a sample. The first pulse, called the pump pulse, rearranges how electrons are distributed in the sample. The second pulse, called the probe pulse, investigates the effects these rearrangements have on the motions of the sample’s electrons and atomic nuclei. By repeating the experiment with varying time delays between the pulses, researchers can make a stop-motion movie of the tiny, fast motions.

    One of the challenges is that X-ray lasers generate light pulses in a random process, so that each pulse is actually a train of narrow X-ray spikes whose intensities vary randomly between pulses.

    “Pump-probe experiments therefore typically require that we first prepare well-defined, short pulses that are less random,” said SLAC’s Daniel Ratner, the study’s lead author. “In addition we need to control the time delay between them very well.”

    In the new approach, he said, “We wouldn’t have to worry about any of that. We would use X-ray pulses as they come out of the XFEL without further modifications.”

    In fact, in this new way of thinking each pair of spikes within a single X-ray pulse can be considered a pair of pump and probe pulses, so researchers could do many pump-probe measurements with a single shot of the XFEL.

    2
    Simulated profile of an X-ray pulse from an X-ray free-electron laser. It consists of a train of narrow spikes whose intensity (power) fluctuates randomly. SLAC researchers suggest using pairs of these spikes for pump-probe experiments that trigger and measure structural changes in a sample, turning a former nuisance into an advantage. This example highlights three pairs of spikes with different time delays between them. (DOI: 10.1103/PhysRevX.9.01104 [N/A])

    Taking ghostly snapshots

    To produce snapshots of a sample’s molecular motions with this method, Ratner and his coworkers want to apply the technique of ghost imaging.

    In conventional imaging, light falling on an object produces a two-dimensional image on a detector – whether the back of your eye, the megapixel sensor in your cell phone or an advanced X-ray detector. Ghost imaging, on the other hand, constructs an image by analyzing how random patterns of light shining onto the object affect the total amount of light coming off the object.

    “In our method, the random patterns are the fluctuating spike structures of individual XFEL pulses,” said co-author Siqi Li, a graduate student at SLAC and Stanford and lead author of a previous study that demonstrated ghost imaging using electrons [Physical Review Letters]. “To do the image reconstruction, we need to repeat the experiment many times – about 100,000 times in our simulations. Each time, we measure the pulse profile with a diagnostic tool and analyze the signal emitted by the sample.”

    In a computational process that borrows ideas from machine learning, researchers can then turn these data into a visualization of the X-ray pulse’s effects on the sample.

    3
    In conventional imaging (left), light falling on an object produces a two-dimensional image on a detector. Ghost imaging (right) constructs an image by analyzing how random patterns of light shining onto the object affect the total amount of light coming off the object. (Greg Stewart/SLAC National Accelerator Laboratory)

    A complementary tool

    So far, the new idea has been tested only in simulations and awaits experimental validation, for instance at SLAC’s Linac Coherent Light Source (LCLS) X-ray laser, a DOE Office of Science user facility.

    SLAC LCLS

    Yet, the researchers are already convinced their method could complement conventional pump-probe experiments.

    “If future tests are successful, the method could strengthen our ability to look at very fundamental processes in XFEL experiments,” Ratner said. “It would also offer a few advantages that we would like to explore.” These include more stability, faster image reconstruction, less sample damage and the prospect of doing experiments at faster and faster timescales.

    Other co-authors of the paper are SLAC’s TJ Lane and Gennady Stupakov. The project was financially supported by the DOE Office of Science.

    See the full article here .


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    Please help promote STEM in your local schools.

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    SLAC/LCLS


    SLAC/LCLS II projected view


    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.

     
  • richardmitnick 7:29 am on March 14, 2019 Permalink | Reply
    Tags: "A new lens on materials under extreme conditions allows researchers to watch shock waves travel through silicon", , Elasticity in silicon shock wave, SLAC LCLS,   

    From SLAC National Accelerator Lab: “A new lens on materials under extreme conditions allows researchers to watch shock waves travel through silicon” 

    From SLAC National Accelerator Lab

    March 13, 2019
    Ali Sundermier

    1
    After blasting silicon with intense laser pulses at SLAC’s Linac Coherent Light Source, researchers saw an unexpected shock wave appear in the material before its structure was irreversibly changed. (Gregory Stewart/SLAC National Accelerator Laboratory)

    Elasticity, the ability of an object to bounce back to its original shape, is a universal property in solid materials. But when pushed too far, materials change in unrecoverable ways: Rubber bands snap in half, metal frames bend or melt and phone screens shatter.

    For instance, when silicon, an element abundant in the Earth’s crust, is subjected to extreme heat and pressure, an initial “elastic” shock wave travels through the material, leaving it unchanged, followed by an “inelastic” shock wave that irreversibly transforms the structure of the material.

    Using a new technique, researchers were able to directly watch and image this process. To their surprise, they discovered that it included an extra step that had not been seen before: After the first elastic shock wave traveled through the silicon, a second elastic wave appeared before the final inelastic wave changed the material’s properties.

    Their results were published in Science Advances last week.

    “We discovered that this transformation is more nuanced than previously thought,” says Shaughnessy Brennan Brown, a postdoctoral candidate at Stanford University and graduate research associate at the Department of Energy’s SLAC National Accelerator Laboratory who led the analysis. “We illuminated an entirely new feature potentially observable in other materials.”

    Seeing through a new lens

    In addition to contributing to a deeper understanding of silicon, a material that is important in fields like engineering, geophysics and plasma physics, this new technique lights the path for solving problems in other fields.

    “The platform Shaughnessy developed is also useful in areas like meteoritics,” says co-author Arianna Gleason-Holbrook, a staff scientist at the Stanford Institute for Materials and Energy Sciences (SIMES) at SLAC. “Let’s say a large metal impactor, like the remnant core of some planet, hits a terrestrial planet. This technique will allow us to zoom in and spatially walk through the history of that type of shock to answer a number of important questions, like how life gets delivered to a new planet or what happens during asteroid collisions.”

    “It’s almost like you’ve had blurry vision for a while,” she said, “but then you put on glasses and the world opens up. What we’ve done in this paper is provide a new lens on materials properties.”

    Catching the wave

    At SLAC, researchers can see what’s happening deep in the belly of samples by hitting them with ultrafast X-ray laser pulses from the Linac Coherent Light Source (LCLS), and then using the patterns formed by the scattered X-rays to reconstruct images.

    At the Matter in Extreme Conditions (MEC) instrument, researchers blast the samples with intense pulses from a second high-power laser before hitting them with X-rays to watch how materials respond to extreme heat and pressure. In many experiments, researchers position these two lasers nearly parallel to each other. This helps them understand how the material is changing over time but doesn’t give them a clear picture of what these structural transformations actually look like.

    A key feature of the technique used in this paper is that the researchers took advantage of a new laser placement that had been used in previous papers, shooting the pulses from the second laser perpendicular to the X-ray pulses from LCLS. This different vantage point allowed them to watch elusive structural changes to the silicon as they occurred, which is how they imaged the second wave moving through the silicon.

    Wide range of scales

    This new experimental setup also allowed the researchers to magnify what they saw, boosting the resolution of their images and allowing them to get a holistic picture of what was happening to the silicon on a wide range of scales, from the microscopic to the macroscopic.

    To follow up, the researchers will repeat the experiment in much more extreme conditions and apply it to a much broader class of materials to find out if they still see this extra step, which will lead to a better understanding of how materials transform.

    “We’ve been attempting to understand fundamental processes of material transformation without always seeing the whole picture,” Brennan Brown says. “Many scientists use clever techniques to approach the problem from different angles. The beauty of this new platform is its clarity, directness and scope.”

    The team also included researchers from the University of York in England; the University of California, Berkeley; the Deutsches Elektronen-Synchrotron and the University of Hamburg, both in Germany.

    LCLS is a DOE Office of Science user facility. Funding was provided by the DOE Office of Science.

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    SLAC/LCLS


    SLAC/LCLS II projected view


    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.

     
  • richardmitnick 8:30 pm on February 21, 2019 Permalink | Reply
    Tags: , , , , Molecular ensemble, , , , PtPOP, , SLAC LCLS, ,   

    From SLAC National Accelerator Lab: “Researchers watch molecules in a light-triggered catalyst ring ‘like an ensemble of bells’’ 

    From SLAC National Accelerator Lab

    February 21, 2019
    Ali Sundermier

    1
    Synchronized molecules
    When photocatalyst molecules absorb light, they start vibrating in a coordinated way, like an ensemble of bells. Capturing this response is a critical step towards understanding how to design molecules for the efficient transformation of light energy to high-value chemicals. (Gregory Stewart/SLAC National Accelerator Laboratory)

    A better understanding of these systems will aid in developing next-generation energy technologies.

    Photocatalysts ­– materials that trigger chemical reactions when hit by light – are important in a number of natural and industrial processes, from producing hydrogen for fuel to enabling photosynthesis.

    Now an international team has used an X-ray laser at the Department of Energy’s SLAC National Accelerator Laboratory to get an incredibly detailed look at what happens to the structure of a model photocatalyst when it absorbs light.

    The researchers used extremely fast laser pulses to watch the structure change and see the molecules vibrating, ringing “like an ensemble of bells,” says lead author Kristoffer Haldrup, a senior scientist at Technical University of Denmark (DTU). This study paves the way for deeper investigation into these processes, which could help in the design of better catalysts for splitting water into hydrogen and oxygen for next-generation energy technologies.

    “If we can understand such processes, then we can apply that understanding to developing molecular systems that do tricks like that with very high efficiency,” Haldrup says.

    The results published last week in Physical Review Letters.

    Molecular ensemble

    The platinum-based photocatalyst they studied, called PtPOP, is one of a class of molecules that scissors hydrogen atoms off various hydrocarbon molecules when hit by light, Haldrup says: “It’s a testbed – a playground, if you will – for studying photocatalysis as it happens.”

    At SLAC’S X-ray laser, the Linac Coherent Light Source (LCLS), the researchers used an optical laser to excite the platinum-containing molecules and then used X-rays to see how these molecules changed their structure after absorbing the visible photons.

    SLAC/LCLS

    The extremely short X-ray laser pulses allowed them to watch the structure change, Haldrup says.

    The researchers used a trick to selectively “freeze” some of the molecules in their vibrational motion, and then used the ultrashort X-ray pulses to capture how the entire ensemble of molecules evolved in time after being hit with light. By taking these images at different times they can stitch together the individual frames like a stop-motion movie. This provided them with detailed information about molecules that were not hit by the laser light, offering insight into the ultrafast changes occurring in the molecules when they are at their lowest energy.

    Swimming in harmony

    Even before the light hits the molecules, they are all vibrating but out of sync with one another. Kelly Gaffney, co-author on this paper and director of SLAC’s Stanford Synchrotron Radiation Lightsource, likens this motion to swimmers in a pool, furiously treading water.

    SLAC SSRL Campus


    SLAC/SSRL


    SLAC/SSRL

    When the optical laser hits them, some of the molecules affected by the light begin moving in unison and with greater intensity, switching from that discordant tread to synchronized strokes. Although this phenomenon has been seen before, until now it was difficult to quantify.

    “This research clearly demonstrates the ability of X-rays to quantify how excitation changes the molecules,” Gaffney says. “We can not only say that it’s excited vibrationally, but we can also quantify it and say which atoms are moving and by how much.”

    Predictive chemistry

    To follow up on this study, the researchers are investigating how the structures of PtPOP molecules change when they take part in chemical reactions. They also hope to use the information they gained in this study to directly study how chemical bonds are made and broken in similar molecular systems.

    “We get to investigate the very basics of photochemistry, namely how exciting the electrons in the system leads to some very specific changes in the overall molecular structure,” says Tim Brandt van Driel, a co-author from DTU who is now a scientist at LCLS. “This allows us to study how energy is being stored and released, which is important for understanding processes that are also at the heart of photosynthesis and the visual system.”

    A better understanding of these processes could be key to designing better materials and systems with useful functions.

    “A lot of chemical understanding is rationalized after the fact. It’s not predictive at all,” Gaffney says. “You see it and then you explain why it happened. We’re trying to move the design of useful chemical materials into a more predictive space, and that requires accurate detailed knowledge of what happens in the materials that already work.”

    LCLS and SSRL are DOE Office of Science user facilities. This research was supported by DANSCATT; the Independent Research Fund Denmark; the Icelandic Research Fund; the Villum Foundation; and the AMOS program within the Chemical Sciences, Geosciences and Biosciences Division of the DOE Office of Basic Energy Sciences.

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    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.

     
  • richardmitnick 11:19 am on January 15, 2019 Permalink | Reply
    Tags: An effect that Einstein helped discover 100 years ago offers new insight into a puzzling magnetic phenomenon, , , , , SLAC LCLS,   

    From SLAC National Accelerator Lab: “An effect that Einstein helped discover 100 years ago offers new insight into a puzzling magnetic phenomenon” 

    From SLAC National Accelerator Lab

    January 14, 2019
    Ali Sundermier

    1
    At SLAC’s Linac Coherent Light Source, the researchers blasted an iron sample with laser pulses to demagnetize it, then grazed the sample with X-rays, using the patterns formed when the X-rays scattered to uncover details of the process. (Gregory Stewart/SLAC National Accelerator Laboratory)

    2
    Researchers from ETH Zürich in Switzerland used LCLS to show a link between ultrafast demagnetization and an effect that Einstein helped discover 100 years ago. (Dawn Harmer/SLAC National Accelerator Laboratory)

    Using an X-ray laser, researchers watched atoms rotate on the surface of a material that was demagnetized in millionths of a billionth of a second.

    More than 100 years ago, Albert Einstein and Wander Johannes de Haas discovered that when they used a magnetic field to flip the magnetic state of an iron bar dangling from a thread, the bar began to rotate.

    Now experiments at the Department of Energy’s SLAC National Accelerator Laboratory have seen for the first time what happens when magnetic materials are demagnetized at ultrafast speeds of millionths of a billionth of a second: The atoms on the surface of the material move, much like the iron bar did. The work, done at SLAC’s Linac Coherent Light Source (LCLS) X-ray laser, was published in Nature earlier this month.

    SLAC/LCLS

    Christian Dornes, a scientist at ETH Zürich in Switzerland and one of the lead authors of the report, says this experiment shows how ultrafast demagnetization goes hand in hand with what’s known as the Einstein-de Haas effect, solving a longstanding mystery in the field.

    “I learned about these phenomena in my classes, but to actually see firsthand that the transfer of angular momentum actually makes something move mechanically is really cool,” Dornes says. “Being able to work on the atomic scale like this and see relatively directly what happens would have been a total dream for the great physicists of a hundred years ago.”

    Spinning sea of skaters

    At the atomic scale, a material owes its magnetism to its electrons. In strong magnets, the magnetism comes from a quantum property of electrons called spin. Although electron spin does not involve a literal rotation of the electron, the electron acts in some ways like a tiny spinning ball of charge. When most of the spins point in the same direction, like a sea of ice skaters pirouetting in unison, the material becomes magnetic.

    When the magnetization of the material is reversed with an external magnetic field, the synchronized dance of the skaters turns into a hectic frenzy, with dancers spinning in every direction. Their net angular momentum, which is a measure of their rotational motion, falls to zero as their spins cancel each other out. Since the material’s angular momentum must be conserved, it’s converted into mechanical rotation, as the Einstein-de Haas experiment demonstrated.

    Twist and shout

    In 1996, researchers discovered that zapping a magnetic material with an intense, super-fast laser pulse demagnetizes it nearly instantaneously, on a femtosecond time scale. It has been a challenge to understand what happens to angular momentum when this occurs.

    In this paper, the researchers used a new technique at LCLS combined with measurements done at ETH Zürich to link these two phenomena. They demonstrated that when a laser pulse initiates ultrafast demagnetization in a thin iron film, the change in angular momentum is quickly converted into an initial kick that leads to mechanical rotation of the atoms on the surface of the sample.

    3
    At SLAC’s Linac Coherent Light Source, the researchers blasted an iron sample with laser pulses to demagnetize it, then grazed the sample with X-rays, using the patterns formed when the X-rays scattered to uncover details of the process. (Gregory Stewart/SLAC National Accelerator Laboratory)

    According to Dornes, one important takeaway from this experiment is that even though the effect is only apparent on the surface, it happens throughout the whole sample. As angular momentum is transferred through the material, the atoms in the bulk of the material try to twist but cancel each other out. It’s as if a crowd of people packed onto a train all tried to turn at the same time. Just as only the people on the fringe would have the freedom to move, only the atoms at the surface of the material are able to rotate.

    Scraping the surface

    In their experiment, the researchers blasted the iron film with laser pulses to initiate ultrafast demagnetization, then grazed it with intense X-rays at an angle so shallow that it was nearly parallel to the surface. They used the patterns formed when the X-rays scattered off the film to learn more about where angular momentum goes during this process.

    “Due to the shallow angle of the X-rays, our experiment was incredibly sensitive to movements along the surface of the material,” says Sanghoon Song, one of three SLAC scientists who were involved with the research. “This was key to seeing the mechanical motion.”

    To follow up on these results, the researchers will do further experiments at LCLS with more complicated samples to find out more precisely how quickly and directly the angular momentum escapes into the structure. What they learn will lead to better models of ultrafast demagnetization, which could help in the development of optically controlled devices for data storage.

    Steven Johnson, a scientist and professor at ETH Zürich and the Paul Scherrer Institute in Switzerland who co-led the study, says the group’s expertise in areas outside of magnetism allowed them to approach the problem from a different angle, better positioning them for success.

    “There have been numerous previous attempts by other groups to understand this, but they failed because they didn’t optimize their experiments to look for these tiny effects,” Johnson says. “They were swamped by other much larger effects, such as atomic movement due to laser heat. Our experiment was much more sensitive to the kind of motion that results from the angular momentum transfer.”

    LCLS is a DOE Office of Science user facility. This work was supported by NCCR Molecular Ultrafast Science and Technology, a research instrument of the Swiss National Science Foundation.

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    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.

     
  • richardmitnick 10:11 am on November 2, 2018 Permalink | Reply
    Tags: "In materials hit with light", , , individual atoms and vibrations take disorderly paths", , SLAC LCLS, , ,   

    From SLAC Lab: “In materials hit with light, individual atoms and vibrations take disorderly paths” 


    From SLAC Lab

    November 1, 2018
    Glennda Chui

    1
    Two studies with a new X-ray laser technique reveal for the first time how individual atoms and vibrations respond when a material is hit with light. Their surprisingly unpredictable behavior has profound implications for designing and controlling materials. (Greg Stewart/SLAC National Accelerator Laboratory)

    Revealed for the first time by a new X-ray laser technique, their surprisingly unruly response has profound implications for designing and controlling materials.

    Hitting a material with laser light sends vibrations rippling through its latticework of atoms, and at the same time can nudge the lattice into a new configuration with potentially useful properties – turning an insulator into a metal, for instance.

    Until now, scientists assumed this all happened in a smooth, coordinated way. But two new studies show it doesn’t: When you look beyond the average response of atoms and vibrations to see what they do individually, the response, they found, is disorderly.

    Atoms don’t move smoothly into their new positions, like band members marching down a field; they stagger around like partiers leaving a bar at closing time.

    And laser-triggered vibrations don’t simply die out; they trigger smaller vibrations that trigger even smaller ones, spreading out their energy in the form of heat, like a river branching into a complex network of streams and rivulets.

    This unpredictable behavior at a tiny scale, measured for the first time with a new X-ray laser technique at the Department of Energy’s SLAC National Accelerator Laboratory, will have to be taken into account from now on when studying and designing new materials, the researchers said – especially quantum materials with potential applications in sensors, smart windows, energy storage and conversion and super-efficient electrical conductors.

    Two separate international teams, including researchers at SLAC and Stanford University who developed the technique, reported the results of their experiments Sept. 20 in Physical Review Letters and today in Science.

    “The disorder we found is very strong, which means we have to rethink how we study all of these materials that we thought were behaving in a uniform way,” said Simon Wall, an associate professor at the Institute of Photonic Sciences in Barcelona and one of three leaders of the study reported in Science. “If our ultimate goal is to control the behavior of these materials so we can switch them back and forth from one phase to another, it’s much harder to control the drunken choir than the marching band.”

    Lifting the haze

    The classic way to determine the atomic structure of a molecule, whether from a manmade material or a human cell, is to hit it with X-rays, which bounce off and scatter into a detector. This creates a pattern of bright dots, called Bragg peaks, that can be used to reconstruct how its atoms are arranged.

    SLAC’s Linac Coherent Light Source (LCLS), with its super-bright and ultrafast X-ray laser pulses, has allowed scientists to determine atomic structures in ever more detail.

    SLAC/LCLS

    They can even take rapid-fire snapshots of chemical bonds breaking, for instance, and string them together to make “molecular movies.”

    About a dozen years ago, David Reis, a professor at SLAC and Stanford and investigator at the Stanford Institute for Materials and Energy Sciences (SIMES), wondered if a faint haze between the bright spots in the detector – 10,000 times weaker than those bright spots, and considered just background noise – could also contain important information about rapid changes in materials induced by laser pulses.

    He and SIMES scientist Mariano Trigo went on to develop a technique called “ultrafast diffuse scattering” that extracts information from the haze to get a more complete picture of what’s going on and when.

    The two new studies represent the first time the technique has been used to observe details of how energy dissipates in materials and how light triggers a transition from one phase, or state, of a material to another, said Reis, who along with Trigo is a co-author of both papers. These responses are interesting both for understanding the basic physics of materials and for developing applications that use light to switch the properties of materials on and off or convert heat to electricity, for instance.

    “It’s sort of like astronomers studying the night sky,” said Olivier Delaire, an associate professor at Duke University who helped lead one of the studies. “Previous studies could only see the brightest stars visible to the naked eye. But with the ultrabright and ultrafast X-ray pulses, we were able to see the faint and diffuse signals of the Milky Way galaxy between them.”

    Tiny bells and piano strings

    In the study published in Physical Review Letters, Reis and Trigo led a team that investigated vibrations called phonons that rattle the atomic lattice and spread heat through a material.

    The researchers knew going in that phonons triggered by laser pulses decay, releasing their energy throughout the atomic lattice. But where does all that energy go? Theorists proposed that each phonon must trigger other, smaller phonons, which vibrate at higher frequencies and are harder to detect and measure, but these had never been seen in an experiment.

    To study this process at LCLS, the team hit a thin film of bismuth with a pulse of optical laser light to set off phonons, followed by an X-ray laser pulse about 50 quadrillionths of a second later to record how the phonons evolved. The experiments were led by graduate student Tom Henighan and postdoctoral researcher Samuel Teitelbaum of the Stanford PULSE Institute.

    For the first time, Trigo said, they were able to observe and measure how the initial phonons distributed their energy over a wider area by triggering smaller vibrations. Each of those small vibrations emanated from a distinct patch of atoms, and the size of the patch – whether it contained 7 atoms, or 9, or 20 – determined the frequency of the vibration. It was much like how ringing a big bell sets smaller bells tinkling nearby, or how plucking a piano string sets other strings humming.

    “This is something we’ve been waiting years to be able to do, so we were excited,” Reis said. “It’s a measurement of something absolutely fundamental to modern solid-state physics, for everything from how heat flows in materials to even, in principle, how light-induced superconductivity emerges, and it could not have been done without an X-ray free-electron laser like LCLS.”

    A disorderly march

    The paper in Science describes LCLS experiments with vanadium dioxide, a well-studied material that can flip from being an insulator to an electrical conductor in just 100 quadrillionths of a second.

    Researchers already knew how to trigger this switch with very short, ultrafast pulses of laser light. But until now they could only observe the average response of the atoms, which seemed to shuffle into their new positions in an orderly way, said Delaire, who led the study with Wall and Trigo.

    The new round of diffuse scattering experiments at LCLS showed otherwise. By hitting the vanadium dioxide with an optical laser of just the right energy, the researchers were able to trigger a substantial rearrangement of the vanadium atoms. They did this more than 100 times per second while recording the movements of individual atoms with the LCLS X-ray laser. They discovered that each atom followed an independent, seemingly random path to its new lattice position. Computer simulations by Duke graduate student Shan Yang backed up that conclusion.

    “Our findings suggest that disorder may play an important role in some materials,” the team wrote in the Science paper. While this may complicate efforts to control the way materials shift from one phase to another, they added, “it could ultimately provide a new perspective on how to control matter,” and even suggest a new way to induce superconductivity with light.

    In a commentary accompanying the report in Science, Andrea Cavalleri of Oxford University and the Max Planck Institute for the Structure and Dynamics of Matter said the results imply that molecular movies of atoms changing position over time don’t paint a complete picture of the microscopic physics involved.

    He added, “More generally, it is clear from this work that x-ray free electron lasers are opening up far more than what was envisaged when these machines were being planned, forcing us to reevaluate many old notions taken for granted up to now.”

    The study published in PRL also involved researchers from Imperial College London; Tyndall National Institute in Ireland; and the University of Michigan, Ann Arbor. Preliminary measurements were performed at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL). Major funding came from the DOE Office of Science.

    SLAC/SSRL

    The study published in Science also involved researchers at the Japan Synchrotron Radiation Research Institute and the DOE’s Oak Ridge National Laboratory. Calculations were performed using resources of the DOE’s National Energy Research Scientific Computing Center (NERSC), and computer simulations used resources of the Oak Ridge Leadership Computing Facility. Major funding came from the European Research Council under the European Union’s Horizon 2020 research and innovation program and from the DOE Office of Science.

    LCLS, SSRL and NERSC are DOE Office of Science user facilities.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

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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.

     
  • richardmitnick 10:42 pm on October 2, 2018 Permalink | Reply
    Tags: , , , , , , SLAC LCLS,   

    From SLAC National Accelerator Lab: “Peering into 36-million-degree plasma with SLAC’s X-ray laser” 

    From SLAC National Accelerator Lab

    October 2, 2018
    Ali Sundermier
    For commnication
    communications@slac.stanford.edu

    1
    At the Matter in Extreme Conditions (MEC) instrument at LCLS, the researchers zapped knuckle-shaped samples with a laser to create plasma, then used an X-ray scattering technique to watch it expand and collide. (Matt Beardsley/SLAC National Accelerator Laboratory)

    When you hit a piece of metal with a strong enough laser pulse you get a plasma – a hot, ionized gas found in everything from lightning to the sun. Studying it helps scientists understand what’s going on inside stars and could enable new types of particle accelerators for cancer treatment.

    Now a team of researchers has used an X-ray laser to measure, for the first time, how a plasma created by a laser blast expands in the hundreds of femtoseconds (quadrillionths of a second) after it’s created. Their technique could eventually reveal tiny instabilities in the plasma that swirl like cream in a cup of coffee.

    The experiments at the Department of Energy’s SLAC National Accelerator Laboratory involved scientists from SLAC, German research center Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and other institutions, and was reported in Physical Review X in September.

    Blasting cancer cells

    Led by scientist Thomas Kluge at HZDR, the researchers have been working to harness the behavior of plasma to create a new type of particle accelerator for proton therapy, an existing cancer treatment that involves blasting tumors with charged particles rather than X-rays. This approach is gentler on the surrounding healthy tissue than traditional radiation therapy.

    When solid matter is zapped with a laser the interaction forms a plasma, causing a steady stream of protons to burst out of the back side of the sample. The researchers hope to use the proton streams to storm tumors and obliterate cancer cells. But producing these fast protons in a reliable way requires a better understanding of how plasma changes as it expands.

    “Instabilities can arise from the complex streams of electrons and ions moving back and forth in the plasma,” Kluge says. “You probably know one of these instabilities from the mushroom-shaped clouds that form when you drip milk into your morning coffee.”

    Hotter than ever

    Until now, it was difficult to probe plasma changes directly because they’re so tiny and happen on extremely fast time scales. This work, says Josefine Metzkes-Ng, co-author and junior group leader at HZDR, could only be done at SLAC where the researchers used a high-power, short-pulse optical laser beam to create the plasma and the Linac Coherent Light Source X-ray free-electron laser to probe it.

    SLAC/LCLS

    At the Matter in Extreme Conditions (MEC) instrument at LCLS, researchers create incredibly hot and dense matter that mimics the extreme conditions in the hearts of stars and planets. Simulations show that the researchers achieved a new temperature record for matter studied with a free-electron laser: 36 million degrees Fahrenheit, almost 10 million degrees hotter than the sun’s core.

    The researchers fabricated solid samples that consisted of raised silicon bars, like knuckles sticking out from a fist. They found that in the quadrillionths of seconds after they zapped the sample with intense, short pulses from the optical laser, tiny amounts of plasma stacked up between the knuckles. A special form of scattering that uses X-ray pulses from LCLS allowed them to peer inside the plasma to follow its evolution.

    This technique will pave the way for better understanding plasma instabilities, allowing researchers to create proton sources for cancer therapy with relatively small footprints that, unlike conventional accelerators, can be operated within a hospital. It will also be useful in research relevant to fusion energy, other types of novel particle accelerators and laboratory astrophysics.

    Speedy cosmic particles

    Siegfried Glenzer, director of the High Energy Density Division at SLAC, who helped with the paper, is especially excited about the prospect of using this technique to better understand the astrophysical processes that give cosmic rays – subatomic space particles that plunge into Earth’s atmosphere at almost the speed of light – their extreme energies.

    The highest-energy cosmic rays can pack a force comparable to that of a major league fastball hurtling toward a batter at 100 mph, condensed into a single subatomic particle. To accelerate a proton to the same energies as these cosmic rays, scientists would have to build an accelerator that sends particles traveling from Earth to Saturn and back.

    Using LCLS, scientists are able to recreate some of the astrophysical processes that may produce these high-energy cosmic rays, such as energetic jets that shoot out from the turbulent hearts of active galaxies. Now the new technique will allow them to directly observe the plasma instabilities that might be responsible for accelerating cosmic rays.

    “Cosmic rays are the largest particle accelerators known to mankind,” Glenzer says. “They have a million times higher energy than particles accelerated in the Large Hadron Collider. Recently, astronomers traced a cosmic ray particle to an active galactic nucleus jet. Our goal is to produce these types of jets in the laboratory so we can study the formation of these instabilities and show whether they can accelerate particles to such high energies and, if so, how it happens.”

    Flipping the light switch

    According to Kluge, “This research has opened the black box of how short-pulse lasers interact with solids, allowing us to directly see a little of what’s going on, which previously could only be simulated with largely unverified atomic models.

    “It’s a little like switching on a light,” he says. “Although we have some ideas, we don’t know what we will find, but surely it will help us develop the next generation of laser-based ion accelerators and could shape new applications in astrophysics, medicine and plasma physics. For me as a theorist and simulation guy, the most exciting thing about this project is that I can now lay my simulations aside and look at the real thing.”

    The research team also included scientists from Technical University Dresden, European XFEL, University of Siegen, Friedrich Schiller University Jena and Leibniz Institute of Photonic Technology, all in Germany.

    LCLS is a DOE Office of Science user facility. Funding was provided by the DOE Office of Science.

    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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