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  • richardmitnick 11:12 am on June 20, 2019 Permalink | Reply
    Tags: , , , ComCam miniature camers for the LSST, , , SLAC   

    From SLAC: “A miniature camera for the Large Synoptic Survey Telescope will help test the observatory and take first images” 

    June 19, 2019
    By Aiko Takeuchi-Demirci

    SLAC completed its work on ComCam, a commissioning device to be installed in Chile later this year.

    LSST ComCam

    Scientists at the Department of Energy’s SLAC National Accelerator Laboratory are building the world’s largest digital camera for astronomy and astrophysics – a minivan-sized 3,200-megapixel ‘eye’ of the future Large Synoptic Survey Telescope (LSST) that will enable unprecedented views of the universe starting in the fall of 2022 and provide new insights into dark energy and other cosmic mysteries.

    LSST Camera, being built at SLAC

    In the meantime, the lab has completed its work on a miniature version that will soon be used for testing the telescope and taking LSST’s first images of the night sky.

    These images will include glimpses of the motions of asteroids and objects in our solar system with orbits beyond that of Neptune, as well as alerts of sudden events such as supernovae, exploding stars that temporarily light up parts of the sky.


    ComCam, a commissioning camera for LSST. (Farrin Abbott/SLAC National Accelerator Laboratory)

    The device, called ComCam (short for Commissioning Camera), will use only four percent of the full LSST camera’s focal plane and produce much smaller images, but it will provide enough “imaging power” to test the observatory while its ultimate camera is still under construction. In fact, ComCam’s 144 megapixels outnumber the pixel count that was available to the Sloan Digital Sky Survey, a pioneering astrophysical survey project in the early 2000s.

    “ComCam will give us a great head start in checking all of the interfaces between the camera, telescope, site infrastructure and data management,” says Kevin Reil, LSST commissioning scientist and SLAC staff scientist.

    After completing the integration of imaging sensors into ComCam and other tasks, the SLAC team today shipped the device to LSST headquarters in Tucson, Arizona. There, more components will be added before the finished ComCam is sent to its final destination in Chile later this year.

    A miniature LSST camera

    The extraordinarily high image quality of the full LSST camera will be largely due to its 189 state-of-the-art imaging sensors. Arranged into square arrays, called rafts, of nine sensors each, they’ll make up the camera’s focal plane. ComCam has only a single raft, which was provided by DOE’s Brookhaven National Laboratory and recently inserted into the ComCam cryostat at SLAC.

    The cryostat, specially designed and built for ComCam, holds the raft in place and cools its imaging sensors to very low temperatures to eliminate unwanted background signals and improve image quality. The ComCam cryostat uses a different refrigeration system from that of the final LSST camera, which requires a more complex system in order to handle 21 rafts.

    The raft also contains electronics boards that will digitize data taken with ComCam. These data will be sent to data management systems at the National Science Foundation-supported National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign and centers at France’s National Institute of Nuclear and Particle Physics and in Chile, where they will be analyzed by scientists around the world.

    SLAC is also building and testing the camera control system, which will allow the observatory software to send commands to ComCam, for instance, to change filters and take images. The LSST camera will use the same control system.

    Toward first images

    Once ComCam arrives in Tucson, LSST scientists will add lenses, a filter changer and a shutter. They will integrate the complete instrument with the observatory software and computing infrastructure and perform crucial tests, including a dry run that will simulate a night of observations.

    “In large projects like LSST, it’s exciting to watch the hardware and software come together into a working system over the years,” says Brian Stalder, LSST commissioning scientist in Tucson.

    Finally, ComCam will be sent to Chile and installed on the actual telescope, paving the way for LSST commissioning.

    In addition, it’ll produce LSST’s first images, albeit at a much smaller scale than the final camera. Although science studies won’t be ComCam’s primary purpose, the team expects the camera to produce images of very good quality, Reil says: “It’ll be exciting to see these early images taken with our brand new, world-class telescope.”

    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, , 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.

    1
    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).

    2
    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 .


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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 10:13 am on January 8, 2019 Permalink | Reply
    Tags: , , , Infrared spectroscopy, , SLAC, ,   

    From SLAC National Accelerator Lab: “Study shows single atoms can make more efficient catalysts” 

    From SLAC National Accelerator Lab

    January 7, 2019
    Glennda Chui

    1
    Scientists used a combination of four techniques, represented here by four incoming beams, to reveal in unprecedented detail how a single atom of iridium catalyzes a chemical reaction. (Greg Stewart/SLAC National Accelerator Laboratory)

    Detailed observations of iridium atoms at work could help make catalysts that drive chemical reactions smaller, cheaper and more efficient.

    Catalysts are chemical matchmakers: They bring other chemicals close together, increasing the chance that they’ll react with each other and produce something people want, like fuel or fertilizer.

    Since some of the best catalyst materials are also quite expensive, like the platinum in a car’s catalytic converter, scientists have been looking for ways to shrink the amount they have to use.

    Now scientists have their first direct, detailed look at how a single atom catalyzes a chemical reaction. The reaction is the same one that strips poisonous carbon monoxide out of car exhaust, and individual atoms of iridium did the job up to 25 times more efficiently than the iridium nanoparticles containing 50 to 100 atoms that are used today.

    The research team, led by Ayman M. Karim of Virginia Tech, reported the results in Nature Catalysis.

    “These single-atom catalysts are very much a hot topic right now,” said Simon R. Bare, a co-author of the study and distinguished staff scientist at the Department of Energy’s SLAC National Accelerator Laboratory, where key parts of the work took place. “This gives us a new lens to look at reactions through, and new insights into how they work.”

    Karim added, “To our knowledge, this is the first paper to identify the chemical environment that makes a single atom catalytically active, directly determine how active it is compared to a nanoparticle, and show that there are very fundamental differences – entirely different mechanisms – in the way they react.”

    Is smaller really better?

    Catalysts are the backbone of the chemical industry and essential to oil refining, where they help break crude oil into gasoline and other products. Today’s catalysts often come in the form of nanoparticles attached to a surface that’s porous like a sponge – so full of tiny holes that a single gram of it, unfolded, might cover a basketball court. This creates an enormous area where millions of reactions can take place at once. When gas or liquid flows over and through the spongy surface, chemicals attach to the nanoparticles, react with each other and float away. Each catalyst is designed to promote one specific reaction over and over again.

    But catalytic reactions take place only on the surfaces of nanoparticles, Bare said, “and even though they are very small particles, the expensive metal on the inside of the nanoparticle is wasted.”

    Individual atoms, on the other hand, could offer the ultimate in efficiency. Each and every atom could act as a catalyst, grabbing chemical reactants and holding them close together until they bond. You could fit a lot more of them in a given space, and not a speck of precious metal would go to waste.

    Single atoms have another advantage: Unlike clusters of atoms, which are bound to each other, single atoms are attached only to the surface, so they have more potential binding sites available to perform chemical tricks – which in this case came in very handy.

    Research on single-atom catalysts has exploded over the past few years, Karim said, but until now no one has been able to study how they function in enough detail to see all the fleeting intermediate steps along the way.

    Grabbing some help

    To get more information, the team looked at a simple reaction where single atoms of iridium split oxygen molecules in two, and the oxygen atoms then react with carbon monoxide to create carbon dioxide.

    They used four approaches­ – infrared spectroscopy, electron microscopy, theoretical calculations and X-ray spectroscopy with beams from SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL) – to attack the problem from different angles, and this was crucial for getting a complete picture.

    SLAC/SSRL

    SLAC SSRL Campus

    “It’s never just one thing that gives you the full answer,” Bare said. “It’s always multiple pieces of the jigsaw puzzle coming together.”

    The team discovered that each iridium atom does, in fact, perform a chemical trick that enhances its performance. It grabs a single carbon monoxide molecule out of the passing flow of gas and holds onto it, like a person tucking a package under their arm. The formation of this bond triggers tiny shifts in the configuration of the iridium atom’s electrons that help it split oxygen, so it can react with the remaining carbon monoxide gas and convert it to carbon dioxide much more efficiently.

    More questions lie ahead: Will this same mechanism work in other catalytic reactions, allowing them to run more efficiently or at lower temperatures? How do the nature of the single-atom catalyst and the surface it sits on affect its binding with carbon monoxide and the way the reaction proceeds?

    The team plans to return to SSRL in January to continue the work.

    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 3:52 pm on April 9, 2018 Permalink | Reply
    Tags: , , SLAC, , , Superconducting electron gun   

    From SLAC: “SLAC Produces First Electron Beam with Superconducting Electron Gun” 


    SLAC Lab

    1
    Image of the first electron beam (bright colors) produced with a superconducting electron gun at SLAC and analyzed with an energy spectrometer. The beam energy was more than a million electronvolts. (SLAC National Accelerator Laboratory)

    April 9, 2018
    Manuel Gnida

    Making a high-quality beam of high-energy electrons starts with an electron gun: It knocks electrons out of atoms with a laser beam so they can be accelerated to nearly the speed of light for experiments that explore nature’s fastest atomic processes.

    Now accelerator scientists at the Department of Energy’s SLAC National Accelerator Laboratory are testing a new type of electron gun for a future generation of instruments that take snapshots of the atomic world in never-before-seen quality and detail, with applications in chemistry, biology, energy and materials science.

    Unlike other electron sources at SLAC, the new one is superconducting: When chilled to extremely low temperatures, some of its key components conduct electricity with nearly 100 percent efficiency. This allows it to produce superior, almost continuous electron beams that will be needed for future high-energy X-ray lasers and ultrafast electron microscopes. The new superconducting electron gun recently produced its first beam of electrons at SLAC.

    “This is an important milestone,” says Xijie Wang, who leads the project. “The use of superconducting accelerator technology represents the beginning of a new era at the lab that will create unforeseen research opportunities, and will keep us at the forefront of science for decades to come.”

    2
    SLAC’s accelerator scientists are testing a superconducting electron gun (inside the large vessel at center), a new type of electron source that could be used in next-generation X-ray lasers and ultrafast electron microscopes. (Dawn Harmer/SLAC National Accelerator Laboratory)

    A Superior Electron Source

    At SLAC and other labs, beams of high-energy electrons are used as tools to precisely examine the atomic fabric of our world and to look at atomic-scale processes that occur within femtoseconds, or millionths of a billionth of a second. The beams are used directly, in instruments for ultrafast electron diffraction and microscopy (UED/UEM), or indirectly in X-ray lasers like SLAC’s Linac Coherent Light Source (LCLS), where the energy of the electron beam is converted into powerful X-ray light.

    SLAC LCLS

    In both approaches, the electrons are produced with an electron gun. It consists of a photocathode, where electrons are released when a metal is hit by a laser pulse; a hollow metal cavity, which accelerates the electrons with a radiofrequency field; and a magnetic lens that bundles the electrons into a tight beam.

    Conventional electron guns use cavities made of normal-conducting metals like copper. But the new device’s cavity is made of niobium, which becomes superconducting at temperatures close to absolute zero. Several groups around the world are actively pursuing the superconducting technology for next-generation particle accelerators and X-ray lasers.

    “Superconducting electron guns have the potential to outperform current guns,” says accelerator physicist Theodore Vecchione, coordinator of the SLAC project. “For instance, while the electron gun that’s being installed as part of the future LCLS-II will generate electron pulses at an extremely high repetition rate, the superconducting gun should be able to produce similar pulses at four times higher beam energy.

    SLAC/LCLS II projected view

    It should also be able to achieve twice the beam acceleration over a given distance, producing a tighter beam of electrons with extraordinary average brightness.”

    3
    SLAC schematic of superconducting electron gun

    LCLS-II will already use superconducting cryomodules to bring electrons up to speed, which will allow the X-ray laser to fire 8,000 times faster after the upgrade. A superconducting electron gun could be ready for a future high-energy upgrade that would further enhance its scientific potential.

    “In addition to advancing X-ray science, the superconducting technology could also turn into an electron source for the UED/UEM techniques we’re developing,” says SLAC accelerator physicist Renkai Li. “It would further improve the quality of atomic-level images and movies we’re able to capture now.”

    A Top R&D Priority

    The SLAC team is testing a superconducting gun that was originally built for a project at the University of Wisconsin, Madison. About two years ago, the DOE relocated the gun to SLAC, asking the lab to recommission it for R&D work in the field of future electron sources.

    “There is a lot of excitement at the lab and the DOE about the opportunity to develop the superconducting technology into something that will drive future applications that require powerful electron beams,” says Bruce Dunham, associate lab director for SLAC’s Accelerator Directorate. “It’s very exciting to see the new gun produce its first electron beam, as it represents the very first step toward that future.”

    Over the past few months, the team installed the gun at SLAC’s Next Linear Collider Test Accelerator (NLCTA) facility and built an experimental setup with diagnostics needed to analyze the generated electron beam. “This successful effort involved many different groups around the lab, including people working on lasers, metrology, vacuum and controls,” says Keith Jobe, the NLCTA facility manager. “We’re also grateful to Bob Legg and other members of the original Wisconsin team, who were very helpful in getting this effort underway here.”

    Now that the team has demonstrated the superconducting gun is working and capable of producing electron beams with energies above a million electronvolts, they are planning their next steps. They first want to make a number of upgrades to improve the gun’s performance, including an overhaul of its refrigeration system. Then, they will be ready to push the technology to higher beam energies that could pave the way for future applications.

    The project is funded by the DOE Office of Science. LCLS is a DOE Office of Science user facility.

    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.

     
  • richardmitnick 8:31 pm on March 20, 2018 Permalink | Reply
    Tags: , , , SLAC, strontium titanate, Weird Superconductor Leads Double Life   

    From SLAC: “Weird Superconductor Leads Double Life” 


    SLAC Lab

    March 20, 2018
    Glennda Chui

    1
    One unusual property of superconducting materials is that they expel magnetic fields and thus cause magnets to levitate, as shown here. A study at SLAC and Stanford of a particularly odd superconductor, strontium titanate, will aid understanding and development of these materials. (ViktorCap/iStock)

    Understanding strontium titanate’s odd behavior will aid efforts to develop materials that conduct electricity with 100 percent efficiency at higher temperatures.

    Until about 50 years ago, all known superconductors were metals. This made sense, because metals have the largest number of loosely bound “carrier” electrons that are free to pair up and flow as electrical current with no resistance and 100 percent efficiency – the hallmark of superconductivity.

    Then an odd one came along – strontium titanate, the first oxide material and first semiconductor found to be superconducting. Even though it doesn’t fit the classic profile of a superconductor – it has very few free-to-roam electrons – it becomes superconducting when conditions are right, although no one could explain why.

    Now scientists have probed the superconducting behavior of its electrons in detail for the first time. They discovered it’s even weirder than they thought. Yet that’s good news, they said, because it gives them a new angle for thinking about what’s known as “high temperature” superconductivity, a phenomenon that could be harnessed for a future generation of perfectly efficient power lines, levitating trains and other revolutionary technologies.

    The research team, led by scientists at the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University, described their study in a paper published Jan. 30 in the Proceedings of the National Academy of Sciences.

    “If conventional metal superconductors are at one end of a spectrum, strontium titanate is all the way down at the other end. It has the lowest density of available electrons of any superconductor we know about,” said Adrian Swartz, a postdoctoral researcher at the Stanford Institute for Materials and Energy Science (SIMES) who led the experimental part of the research with Hisashi Inoue, a Stanford graduate student at the time.

    “It’s one of a large number of materials we call ‘unconventional’ superconductors because they can’t be explained by current theories,” Swartz said. “By studying its extreme behavior, we hope to gain insight into the ingredients that lead to superconductivity in these unconventional materials, including the ones that operate at higher temperatures.”

    Dueling Theories

    According to the widely accepted theory known as BCS for the initials of its inventors, conventional superconductivity is triggered by natural vibrations that ripple through a material’s atomic latticework. The vibrations cause carrier electrons to pair up and condense into a superfluid, which flows through the material with no resistance – a 100-percent-efficient electric current. In this picture, the ideal superconducting material contains a high density of fast-moving electrons, and even relatively weak lattice vibrations are enough to glue electron pairs together.

    But outside the theory, in the realm of unconventional superconductors, no one knows what glues the electron pairs together, and none of the competing theories hold sway.

    To find clues to what’s going on inside strontium titanate, scientists had to figure out how to apply an important tool for studying superconducting behavior, known as tunneling spectroscopy, to this material. That took several years, said Harold Hwang, a professor at SLAC and Stanford and SIMES investigator.

    “The desire to do this experiment has been there for decades, but it’s been a technical challenge,” he said. “This is, as far as I know, the first complete set of data coming out of a tunneling experiment on this material.” Among other things, the team was able to observe how the material responded to doping, a commonly used process where electrons are added to a material to improve its electronic performance.

    ‘Everything is Upside Down’

    The tunneling measurements revealed that strontium titanate is the exact opposite of what you’d expect in a superconductor: Its lattice vibrations are strong and its carrier electrons are few and slow.

    “This is a system where everything is upside down,” Hwang said.

    On the other hand, details like the behavior and density of its electrons and the energy required to form the superconducting state match what you would expect from conventional BCS theory almost exactly, Swartz said.

    “Thus, strontium titanate seems to be an unconventional superconductor that acts like a conventional one in some respects,” he said. “This is quite a conundrum, and quite a surprise to us. We discovered something that was more confusing than we originally thought, which from a fundamental physics point of view is more profound.”

    He added, “If we can improve our understanding of superconductivity in this puzzling set of circumstances, we could potentially learn how to harvest the ingredients for realizing superconductivity at higher temperatures.”

    The next step, Swartz said, is to use tunneling spectroscopy to test a number of theoretical predictions about why strontium titanate acts the way it does.

    SIMES is a joint SLAC/Sanford institute. Theorists from SIMES and from the University of Tennessee, Knoxville also contributed to this study, which was funded by the DOE Office of Science and the Gordon and Betty Moore Foundation’s Emergent Phenomena in Quantum Systems Initiative.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    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 1:42 pm on February 21, 2018 Permalink | Reply
    Tags: , In a First Tiny Diamond Anvils Trigger Chemical Reactions by Squeezing, , SLAC   

    From SLAC: “In a First, Tiny Diamond Anvils Trigger Chemical Reactions by Squeezing” 


    SLAC Lab

    February 21, 2018
    Glennda Chui

    Press Office Contact:
    Andy Freeberg
    afreeberg@slac.stanford.edu
    (650) 926-4359

    Experiments with ‘molecular anvils’ mark an important advance for mechanochemistry, which has the potential to make chemistry greener and more precise.

    1
    An illustration shows complexes of soft molecules (yellow and pink) attached to “molecular anvils” (red and blue) that are about to be squeezed between two diamonds in a diamond anvil cell. The molecular anvils distribute this pressure unevenly, breaking bonds and triggering other chemical reactions in the softer molecules. (Peter Allen/UC-Santa Barbara)

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    A disassembled diamond anvil cell. Each half contains a tiny diamond housed in stainless steel. Samples are placed between the diamond tips; then the cell is closed and the tips squeezed together by tightening screws. This small device can generate pressures in the gigapascal range – 10,000 times the atmospheric pressure at the Earth’s surface. (Dawn Harmer/SLAC National Accelerator Laboratory)

    3
    An animation shows how attaching molecular anvils (gray cages) to softer molecules (red and yellow balls) distributes the pressure from a bigger diamond anvil unevenly, so chemical bonds bend and eventually break around the atom that bears the largest deformation (circled red ball). (Greg Stewart/SLAC National Accelerator Laboratory)

    Scientists have turned the smallest possible bits of diamond and other super-hard specks into “molecular anvils” that squeeze and twist molecules until chemical bonds break and atoms exchange electrons. These are the first such chemical reactions triggered by mechanical pressure alone, and researchers say the method offers a new way to do chemistry at the molecular level that is greener, more efficient and much more precise.

    The research was led by scientists from the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University, who reported their findings in Nature today.

    “Unlike other mechanical techniques, which basically pull molecules until they break apart, we show that pressure from molecular anvils can both break chemical bonds and trigger another type of reaction where electrons move from one atom to another,” said Hao Yan, a physical science research associate at SIMES, the Stanford Institute for Materials and Energy Sciences, and one of the lead authors of the study.

    “We can use molecular anvils to trigger changes at a specific point in a molecule while protecting the areas we don’t want to change,” he said, “and this creates a lot of new possibilities.”

    A reaction that’s mechanically driven has the potential to produce entirely different products from the same starting ingredients than one driven the conventional way by heat, light or electrical current, said study co-author Nicholas Melosh, a SIMES investigator and associate professor at SLAC and Stanford. It’s also much more energy efficient, and because it doesn’t need heat or solvents, it should be environmentally friendly.

    Putting the Squeeze on Materials with Diamonds

    The experiments were carried out with a diamond anvil cell about the size of an espresso cup in the laboratory of paper co-author Wendy Mao, an associate professor at SLAC and Stanford and an investigator with SIMES, which is a joint SLAC/Stanford institute.

    Diamond anvil cells squeeze materials between the flattened tips of two diamonds and can reach tremendous pressures – over 500 gigapascals, or about one and a half times the pressure at the center of the Earth. They’re used to explore what minerals deep inside the Earth are like and how materials under pressure develop unusual properties, among other things.

    These pressures are reached in a surprisingly straightforward way, by tightening screws to bring the diamonds closer together, Mao said. “Pressure is force per unit area, and we are compressing a tiny amount of sample between the tips of two small diamonds that each weigh only about a quarter of a carat,” she said, “so you only need a modest amount of force to reach high pressures.”

    Since the diamonds are transparent, light can go through them and reach the sample, said Yu Lin, a SIMES associate staff scientist who led the high-pressure part of the experiment.

    “We can use a lot of experimental techniques to study the reaction while the sample is compressed,” she said. “For instance, when we shine an X-ray beam into the sample, the sample responds by scattering or absorbing the light, which travels back through the diamond into a detector. Analyzing the signal from that light tells you if a reaction has occurred.”

    3
    Illustration of a diamond anvil cell, where samples can be compressed to very high pressures between the flattened tips of two diamonds. (Argonne National Laboratory, Greg Stewart/SLAC National Accelerator Laboratory)

    What usually happens when you squeeze a sample is that it deforms uniformly, with all the bonds between atoms shrinking by the same amount, Melosh said.

    Yet this is not always the case, he said: “If you compress a material that has both hard and soft components, such as carbon fibers embedded in epoxy, the bonds in the soft epoxy will deform a whole lot more than the ones in the carbon fiber.”

    They wondered if they could harness that same principle to bend or break specific bonds in an individual molecule.

    What got them thinking along those lines was a series of experiments Melosh’s team had done with diamondoids, the smallest possible bits of diamond, which are invisible to the naked eye and weigh less than a billionth of a billionth of a carat. Melosh co-directs a joint SLAC-Stanford program that isolates diamondoids from petroleum fluid and looks for ways to put them to use. In a recent study, his team had attached diamondoids to smaller, softer molecules to create Lego-like blocks that assembled themselves into the thinnest possible electrical wires, with a conducting core of sulfur and copper.

    Like carbon fibers in epoxy, these building blocks contained hard and soft parts. If put into a diamond anvil, would the hard parts act as mini-anvils that squeeze and deform the soft parts in a non-uniform way?

    The answer, they discovered, was yes.

    5
    A disassembled diamond anvil cell. Each half contains a tiny diamond housed in stainless steel. Samples are placed between the diamond tips; then the cell is closed and the tips squeezed together by tightening screws. This small device can generate pressures in the gigapascal range – 10,000 times the atmospheric pressure at the Earth’s surface. (Dawn Harmer/SLAC National Accelerator Laboratory)

    Tiny Anvils Open New Possibilities

    For their first experiments, they used copper sulfur clusters – tiny particles consisting of eight atoms – attached to molecular anvils made of another rigid molecule called carborane. They put this combination into the diamond anvil cell and cranked up the pressure.

    When the pressure got high enough, atomic bonds in the cluster broke, but that’s not all. Electrons moved from its sulfur atoms to its copper atoms and pure crystals of copper formed, which would not have occurred in conventional reactions driven by heat, the researchers said. They discovered a point of no return where this change becomes irreversible. Below that pressure point, the cluster goes back to its original state when pressure is removed.

    Computational studies revealed what had happened: Pressure from the diamond anvil cell moved the molecular anvils, and they in turn squeezed chemical bonds in the clusters, compressing them at least 10 times more than their own bonds had been compressed. This compression was also uneven, Yan said, and it bent or twisted some of the cluster’s bonds in a way that caused bonds to break, electrons to move and copper crystals to form.

    Other experiments, this time with diamondoids as molecular anvils, showed that small changes in the sizes and positions of the tiny anvils can make the difference between triggering a reaction or protecting part of a molecule so it doesn’t bend or react.

    The scientists were able to observe these changes with several techniques, including electron microscopy at Stanford and X-ray measurements at two DOE Office of Science user facilities – the Advanced Light Source at Lawrence Berkeley National Laboratory and the Advanced Photon Source at Argonne National Laboratory.

    LBNL/ALS

    ANL/APS

    6
    Researchers in a SIMES lab with equipment used in the molecular anvil study. From left: Hao Yan, a physical science research associate at SIMES; Nicholas Melosh, a SIMES investigator and associate professor at SLAC and Stanford; and Yu Lin, a SIMES associate staff scientist. (Dawn Harmer/SLAC National Accelerator Laboratory)

    “This is exciting, and it opens up a whole new field,” Mao said. “From our side, we’re interested in looking at how pressure can affect a wide range of technologically interesting materials, from superconductors that transmit electricity with no loss to halide perovskites, which have a lot of potential for next-generation solar cells. Once we understand what’s possible from a very basic science point of view we can think about the more practical side.”

    Going forward, the researchers also want to use this technique to look at reactions that are hard to do in conventional ways and see if compression makes them easier, Yan said.

    “If we want to dream big, could compression help us turn carbon dioxide from the air into fuel, or nitrogen from the air into fertilizer?” he said. “These are some of the questions that molecular anvils will allow people to explore.”

    In addition to SLAC, Stanford, Berkeley Lab and Argonne, researchers who contributed to this study came from the National Autonomous University of Mexico (UNAM), Justus-Liebig University in Germany, Hong Kong University of Science and Technology and the University of Chicago. Major funding came from the DOE Office of Science.

    See the full article here .

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  • richardmitnick 2:28 pm on February 1, 2018 Permalink | Reply
    Tags: , , , , SLAC,   

    From SLAC: “Q&A: Alan Heirich and Elliott Slaughter Take On SLAC’s Big Data Challenges” 


    SLAC Lab

    January 9, 2018
    Manuel Gnida

    1
    Members of SLAC’s Computer Science Division. From left: Alex Aiken, Elliott Slaughter and Alan Heirich. (Dawn Harmer/SLAC National Accelerator Laboratory)

    As the Department of Energy’s SLAC National Accelerator Laboratory builds the next generation of powerful instruments for groundbreaking research in X-ray science, astronomy and other fields, its Computer Science Division is preparing for the onslaught of data these instruments will produce.

    The division’s initial focus is on LCLS-II, an upgrade to the Linac Coherent Light Source (LCLS) X-ray laser that will fire 8,000 times faster than the current version. LCLS-II promises to provide completely new views of the atomic world and its fundamental processes. However, the jump in firing rate goes hand and in hand with an explosion of scientific data that would overwhelm today’s computing architectures.

    SLAC/LCLS

    SLAC/LCLS II projected view

    In this Q&A, SLAC computer scientists Alan Heirich and Elliott Slaughter talk about their efforts to develop new computing capabilities that will help the lab cope with the coming data challenges.

    Heirich, who joined the lab last April, earned a PhD from the California Institute of Technology and has many years of experience working in industry and academia. Slaughter joined last June; he’s a recent PhD graduate from Stanford University, where he worked under the guidance of Alex Aiken, professor of computer science at Stanford and director of SLAC’s Computer Science Division.

    What are the computing challenges you’re trying to solve?

    Heirich: The major challenge we’re looking at now is that LCLS-II will produce so much more data than the current X-ray laser. Data rates will increase 10,000 times, from about 100 megabytes per second today to a terabyte per second in a few years. We need to think about the computing tools and infrastructure necessary to take control over that enormous future data stream.

    Slaughter: Our development of new computing architectures is aimed at analyzing LCLS-II data on the fly, providing initial results within a minute or two. This allows researchers to evaluate the quality of their data quickly, make adjustments and collect data in the most efficient way. However, real-time data analysis is quite challenging if you collect data with an X-ray laser that fires a million pulses per second.
    How can real-time analysis be achieved?

    Slaughter: We won’t be able to do all this with just the computing capabilities we have on site. The plan is to send some of the most challenging LCLS-II data analyses to the National Energy Research Scientific Computing Center (NERSC) at DOE’s Lawrence Berkeley National Laboratory, where extremely fast supercomputers will analyze the data and send the results back to us within minutes.

    Our team has joined forces with Amedeo Perazzo, who leads the LCLS Controls and Data Systems Division, to develop the system that will run the analysis. Scientists doing experiments at LCLS will be able to define the details of that analysis, depending on what their scientific questions are.

    Our goal is to be able to do the analysis in a very flexible way using all kinds of high-performance computers that have completely different hardware and architectures. In the future, these will also include exascale supercomputers that perform more than a billion billion calculations per second – up to a hundred times more than today’s most powerful machines.

    Is it difficult to build such a flexible computing system?

    Heirich: Yes. Supercomputers are very complex with millions of processors running in parallel, and we need to figure out how to make use of their individual architectures most efficiently. At Stanford, we’re therefore developing a programming system, called Legion, that allows people to write programs that are portable across very different high-performance computer architectures.

    Traditionally, if you want to run a program with the best possible performance on a new computer system, you may need to rewrite significant parts of the program so that it matches the new architecture. That’s very labor and cost intensive. Legion, on the other hand, is specifically designed to be used on diverse architectures and requires only relatively small tweaks when moving from one system to another. This approach prepares us for whatever the future of computing looks like. At SLAC, we’re now starting to adapt Legion to the needs of LCLS-II.

    We’re also looking into how we can visualize the scientific data after they are analyzed at NERSC.

    NERSC Cray XC40 Cori II supercomputer

    LBL NERSC Cray XC30 Edison supercomputer


    The Genepool system is a cluster dedicated to the DOE Joint Genome Institute’s computing needs. Denovo is a smaller test system for Genepool that is primarily used by NERSC staff to test new system configurations and software.

    NERSC PDSF


    PDSF is a networked distributed computing cluster designed primarily to meet the detector simulation and data analysis requirements of physics, astrophysics and nuclear science collaborations.

    The analysis will be done on thousands of processors, and it’s challenging to orchestrate this process and put it together into one coherent visual picture. We just presented one way to approach this problem at the supercomputing conference SC17 in November.

    What’s the goal for the coming year?

    Slaughter: We’re working with the LCLS team on building an initial data analysis prototype. One goal is to get a first test case running on the new system. This will be done with X-ray crystallography data from LCLS, which are used to reconstruct the 3-D atomic structure of important biomolecules, such as proteins. The new system will be much more responsive than the old one. It’ll be able to read and analyze data at the same time, whereas the old system can only do one or the other at any given moment.
    Will other research areas besides X-ray science profit from your work?

    Slaughter: Yes. Alex is working on growing our division, identifying potential projects across the lab and expanding our research portfolio. Although we’re concentrating on LCLS-II right now, we’re interested in joining other projects, such as the Large Synoptic Survey Telescope (LSST). SLAC is building the LSST camera, a 3.2-gigapixel digital camera that will capture unprecedented images of the night sky. But it will also produce enormous piles of data – millions of gigabytes per year. Progress in computer science is needed to efficiently handle these data volumes.

    Heirich: SLAC and its close partnership with Stanford Computer Science make for a great research environment. There is also a lot of interest in machine learning. In this form of artificial intelligence, computer programs get better and more efficient over time by learning from the tasks they performed in the past. It’s a very active research field that has seen a lot of growth over the past five years, and machine learning has become remarkably effective in solving complex problems that previously needed to be done by human beings.

    Many groups at SLAC and Stanford are exploring how they can exploit machine learning, including teams working in X-ray science, particle physics, astrophysics, accelerator research and more. But there are very fundamental computer science problems to solve. As machine learning replaces some conventional analysis methods, one big question is, for example, whether the solutions it generates are as reliable as those obtained in the conventional way.

    LCLS and NERSC are DOE Office of Science user facilities. Legion is being developed at Stanford with funding from DOE’s ExaCT Combustion Co-Design Center, Scientific Data Management, Analysis and Visualization program and Exascale Computing Project (ECP) as well as other contributions. SLAC’s Computer Science Division receives funding from the ECP.

    See the full article here .

    Please help promote STEM in your local schools.

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    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 7:40 am on January 31, 2018 Permalink | Reply
    Tags: , Metal 3-D Printing, , SLAC,   

    From SLAC: “SLAC Scientists Investigate How Metal 3-D Printing Can Avoid Producing Flawed Parts” 


    SLAC Lab

    January 30, 2018
    Kimber Price

    1
    A metal 3-D printed sample the team used for experiments. (Johanna Nelson Weker/SLAC)


    Video – 3-D printing of a metal sample inside an X-ray chamber

    This video shows the 3-D printing of a metal sample inside an X-ray characterization chamber at Lawrence Livermore National Laboratory before the chamber was dismantled, transported to SLAC and rebuilt. At SLAC the glass windows were replaced with X-ray transparent beryllium windows. The chamber allows researchers to observe metal 3-D printing in real time. No video credit.


    This video shows the 3-D printing of a metal sample inside an X-ray characterization chamber at Lawrence Livermore National Laboratory before the chamber was dismantled, transported to SLAC and rebuilt. At SLAC the glass windows were replaced with X-ray transparent beryllium windows. The chamber allows researchers to observe metal 3-D printing in real time. No video credit.

    2
    SLAC staff scientist Johanna Nelson Weker, front, leads a study on metal 3-D printing at SLAC’s Stanford Synchrotron Radiation Lightsource with researchers Andrew Kiss and Nick Calta, back. (Dawn Harmer/SLAC).

    SLAC/SSRL

    Pits Among the Layers

    In metal 3-D printing, a thin layer of powdered metal, such as titanium alloys, steel, aluminum alloys, or copper, is distributed on a platform and selectively melted by a high-powered laser beam. Then the platform is lowered, a new layer of metal powder is applied and the process is repeated until the object is fully formed.

    This process often results in the formation of pits, or weak spots, when the metal cools and hardens unevenly while building up the layers. In the SLAC X-ray experiments, scientists are analyzing every aspect of the process ­– the kind of metal used, the level of heat from the laser, the speed at which the metal heats and cools – to find the best combination for eliminating pits, controlling the microstructure, and manufacturing strong metal parts.

    “We are providing the fundamental physics research that will help us identify which aspects of metal 3-D printing are important,” says Chris Tassone, a staff scientist in SSRL’s Materials Science Division. It’s practical information, he says, that could eventually lead to writing recipes for 3-D printer laser settings that manufacturers can use to produce sturdy parts.

    Diving in for a Better View

    Until recently, researchers watched from above as layers were being added to form a part. Because they couldn’t see below the surface of the metal, it was impossible to tell how deeply the laser was melting the layers as each one was applied. They tried imaging the growing layers with thermal radiation, or heat, but this did not give them enough information about what was causing the weak spots. X-rays, however, give researchers an excellent tool to see and record what’s happening inside the part as it’s being built.

    The scientists are using two X-ray methods to see what happens during metal 3-D printing. With one type of X-ray light, they create micron-resolution images of what happens as the layers of metal build up. The second method bounces X-rays off the atoms in the material to analyze its atomic structure as it changes from solid to liquid and back to solid form during the melting and cooling process.

    Thus far, the group has been looking at lasers hitting layers of metal powder, but they also plan to investigate another approach called “directed energy deposition.” In this process, a laser beam hits and melts metal powder or wire as it is being laid down, allowing creation of more complex geometric forms. This sort of 3-D printing is especially useful in making repairs.

    They also want to incorporate a high-speed camera into their experimental setup so they can collect photographs and video of the manufacturing process and correlate what they see with their X-ray data.

    This is important to manufacturers and other researchers who use cameras to observe the process but don’t have access to an X-ray synchrotron, Nelson Weker says: “We want people to be able to connect what they see on their cameras with what we are measuring here so they can infer what’s happening below the surface of the growing metal material. We want to put meaning to those signatures.”

    Other researchers on the metal 3-D printing project include Kevin Stone, Anthony Fong, Andrew Kiss and Vivek Thampy. SSRL is a DOE Office of Science user facility. The research was funded by the DOE Office of Energy Efficiency and Renewable Energy’s Advanced Manufacturing Office.

    See the full article here .

    Please help promote STEM in your local schools.

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    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 2:06 pm on December 12, 2017 Permalink | Reply
    Tags: Electric car makers are intensely interested in lithium-rich battery cathodes that could significantly increase driving range, , Scientists Discover Path to Improving Game-Changing Battery Electrode, SLAC,   

    From SLAC: “Scientists Discover Path to Improving Game-Changing Battery Electrode” 


    SLAC Lab

    Electric car makers are intensely interested in lithium-rich battery cathodes that could significantly increase driving range. A new study opens a path to making them live up to their promise.

    1
    Electric car makers are intensely interested in lithium-rich battery cathodes that could significantly increase driving range. A new study opens a path to making them live up to their promise. (Stanford University/3Dgraphic)

    2
    SLAC and Stanford researchers at an SSRL beamline used for battery research. From left: SLAC staff scientists Apurva Mehta and Kevin Stone; Stanford graduate students Will Gent and Kipil Lim; and SLAC distinguished staff scientist Mike Toney. (Dawn Harmer/SLAC National Accelerator Laboratory)

    December 12, 2017
    If you add more lithium to the positive electrode of a lithium-ion battery – overstuff it, in a sense ­– it can store much more charge in the same amount of space, theoretically powering an electric car 30 to 50 percent farther between charges. But these lithium-rich cathodes quickly lose voltage, and years of research have not been able to pin down why – until now.

    After looking at the problem from many angles, researchers from Stanford University, two Department of Energy national labs and the battery manufacturer Samsung created a comprehensive picture of how the same chemical processes that give these cathodes their high capacity are also linked to changes in atomic structure that sap performance.

    “This is good news,” said William E. Gent, a Stanford University graduate student and Siebel Scholar who led the study. “It gives us a promising new pathway for optimizing the voltage performance of lithium-rich cathodes by controlling the way their atomic structure evolves as a battery charges and discharges.”

    Michael Toney, a distinguished staff scientist at SLAC National Accelerator Laboratory and a co-author of the paper, added, “It is a huge deal if you can get these lithium-rich electrodes to work because they would be one of the enablers for electric cars with a much longer range. There is enormous interest in the automotive community in developing ways to implement these, and understanding what the technological barriers are may help us solve the problems that are holding them back.”

    The team’s report appears today in Nature Communications.

    The researchers studied the cathodes with a variety of X-ray techniques at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL) and Lawrence Berkeley National Laboratory’s Advanced Light Source (ALS).

    SLAC/SSRL

    LBNL/ALS

    Theorists from Berkeley Lab’s Molecular Foundry, led by David Prendergast, were also involved, helping the experimenters understand what to look for and explain their results.

    The cathodes themselves were made by Samsung Advanced Institute of Technology using commercially relevant processes, and assembled into batteries similar to those in electric vehicles.

    “This ensured that our results represented an understanding of a cutting-edge material that would be directly relevant for our industry partners,” Gent said. As an ALS doctoral fellow in residence, he was involved in both the experiments and the theoretical modelling for the study.

    See the full article here .

    Please help promote STEM in your local schools.

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    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 7:48 pm on September 28, 2017 Permalink | Reply
    Tags: , , , SLAC, Stanford PULSE Institute   

    From SLAC: “A Potential New and Easy Way to Make Attosecond Laser Pulses: Focus a Laser on Ordinary Glass” 


    SLAC Lab

    September 28, 2017
    Glennda Chui

    1
    In this illustration, a near-infrared laser beam hits a piece of ordinary glass and triggers a process called high harmonic generation. It produces laser light pulses (top right) that are just billionths of a billionth of a second, or attoseconds, long, and the photons in those pulses are much higher energy than those in the original beam. The insets zoom in on how this happens. When the incoming laser light knocks electrons (e-) out of atoms in the glass, they fly away, loop back and reconnect with either their home atom (lower right) or a neighboring atom (upper left). These reconnections generate bright bursts of light, forming a “train” of attosecond pulses that leaves the glass and can be used to probe electron movements in solids. (Greg Stewart/SLAC National Accelerator Laboratory)

    This novel method could shrink the equipment needed to make laser pulses that are billionths of a billionth of a second long for studying ultra-speedy electron movements in solids, chemical reactions and future electronics.

    The discovery 30 years ago that laser light can be boosted to much higher energies and shorter pulses – just billionths of a billionth of a second, or attoseconds, long – is the basis of attosecond science, where researchers observe and try to control the movements of electrons. Electrons are key players in chemical reactions, biological processes, electronics, solar cells and other technologies, and only pulses this short can make snapshots of their incredibly swift moves.

    Now scientists from the Stanford PULSE Institute at the Department of Energy’s SLAC National Accelerator Laboratory have found a potential new way to make attosecond laser pulses using ordinary glass – in this case, the cover slip from a microscope slide.

    The discovery, reported in Nature Communications today, was a real surprise and opens new possibilities for attosecond science and technology, including the ability to probe ultra-speedy electron motions inside glasses and other solid materials. It could also dramatically shrink the size and cost of the setups needed to produce these tiny pulses, to the point where you might be able to generate pulses inside a fiber optic cable that delivers them to where they’re needed.

    “With today’s methods, you have to shine the laser beam through a special gas jet or through a crystal that has to be grown with great care at ultra-cold temperatures,” said Yong Sing You, a postdoctoral researcher at PULSE and lead author of the study. “But this is exciting because you can use everyday glass, which is cheap and easily available, at room temperature. If you were to put your eyeglasses into the experiment, it would still work, and it would not even damage the glasses.”

    2
    Postdoctoral researcher Yong Sing You, left, and staff scientist Shambhu Ghimire in the PULSE laser lab at SLAC where the experiments were carried out. (Chris Smith/SLAC National Accelerator Laboratory)

    A String of Surprises

    The process that generates attosecond laser pulses is called high harmonic generation, or HHG. Much like pressing on a guitar string produces a note that’s higher in pitch, shining laser light through certain materials changes the nature of the light, shifting it to higher energies and shorter pulses than a laser can reach on its own.

    Most of the time this is done in a gas. Incoming photons, or particles of light, from the laser hit atoms in the gas and liberate some of their electrons. The freed electrons fly away, loop back and reconnect with their home atoms. This reconnection generates attosecond bursts of light that combine to form an attosecond laser pulse.

    Starting in 2010, a series of experiments led by PULSE researchers Shambhu Ghimire and David Reis showed HHG can be produced in ways that were previously thought unlikely or even impossible: by beaming laser light into a crystal, frozen argon gas or an atomically thin semiconductor material.

    Unlike a gas, whose atoms are so far apart that you can think of them as behaving independently, atoms in a solid are so close together that scientists thought electrons freed by an incoming laser pulse would hit neighboring atoms, scatter and never return home to make that crucial reconnection. But it turned out this was not the case, Reis said: “There’s something about the orderly structure of the crystal that allows electrons to move throughout the lattice in a way that doesn’t dissipate their energy or give them a kick in some other direction. Even if they connect with a neighboring atom, they can still participate in HHG.”

    Fundamental Science with Practical Potential

    The fact that glass could generate HHG was also a surprise, said Ghimire, who helped lead the latest study. Because it’s amorphous, meaning that its silicon and oxygen atoms are arranged in no particular order, it did not seem like a good candidate.

    But glass’s random nature was just what the team needed to answer the fundamental scientific question at the heart of the study: How do the density and crystallinity of a material – the degree to which its atoms are arranged in an orderly lattice – independently affect its ability to produce HHG? A piece of glass and a quartz crystal are both made of silicon and oxygen, and they’re roughly the same density; only the arrangement of their atoms is different. So comparing the two should provide some answers.

    The scientists put the glass cover slip in their apparatus and hit it with pulses from their infrared laser beam.

    “You might think, again, that this wouldn’t work, because the electrons would bounce off their neighbors and never make it back home,” said Reis, who was not involved in the current paper. “But the surprising thing is that even in glass, if you hit the glass hard enough but not so hard that you break it, it works fine, although by a slightly different process.”

    The ability to produce HHG in glass and other solids is exciting, he said, because it has the potential to shrink the equipment needed to do this from the size of a lab bench to maybe just a few nanometers – billionths of a meter – in size.

    Ghimire added that producing harmonics in glass has potential technological applications. For instance, it produces the short wavelengths of laser light needed to design masks for patterning nanometer-scale features on semiconductor chips.

    “For this, they want as much intensity as possible, and also an easy way to deliver light to their samples,” he said. “Being able to produce short-wavelength laser light in normal glass would bring us a couple of steps closer to something they could actually use. We could even generate the short-wavelength light in the glass portion of optical fibers that then deliver it to wherever they wanted it.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

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    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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