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  • richardmitnick 10:14 am on March 18, 2019 Permalink | Reply
    Tags: "Exotic “second sound” phenomenon observed in pencil lead", , , Laser Technology, , , There’s good reason to believe that second sound might be more pronounced in graphene even at room temperature., Transient thermal grating   

    From MIT News: “Exotic “second sound” phenomenon observed in pencil lead” 

    MIT News
    MIT Widget

    From MIT News

    March 14, 2019
    Jennifer Chu

    1
    Researchers find evidence that heat moves through graphite similar to the way sound moves through air. Image: Christine Daniloff

    At relatively balmy temperatures, heat behaves like sound when moving through graphite, study reports.

    The next time you set a kettle to boil, consider this scenario: After turning the burner off, instead of staying hot and slowly warming the surrounding kitchen and stove, the kettle quickly cools to room temperature and its heat hurtles away in the form of a boiling-hot wave.

    We know heat doesn’t behave this way in our day-to-day surroundings. But now MIT researchers have observed this seemingly implausible mode of heat transport, known as “second sound,” in a rather commonplace material: graphite — the stuff of pencil lead.

    At temperatures of 120 kelvin, or -240 degrees Fahrenheit, they saw clear signs that heat can travel through graphite in a wavelike motion. Points that were originally warm are left instantly cold, as the heat moves across the material at close to the speed of sound. The behavior resembles the wavelike way in which sound travels through air, so scientists have dubbed this exotic mode of heat transport “second sound.”

    The new results represent the highest temperature at which scientists have observed second sound. What’s more, graphite is a commercially available material, in contrast to more pure, hard-to-control materials that have exhibited second sound at 20 K, (-420 F) — temperatures that would be far too cold to run any practical applications.

    The discovery, published today in Science, suggests that graphite, and perhaps its high-performance relative, graphene, may efficiently remove heat in microelectronic devices in a way that was previously unrecognized.

    “There’s a huge push to make things smaller and denser for devices like our computers and electronics, and thermal management becomes more difficult at these scales,” says Keith Nelson, the Haslam and Dewey Professor of Chemistry at MIT. “There’s good reason to believe that second sound might be more pronounced in graphene, even at room temperature. If it turns out graphene can efficiently remove heat as waves, that would certainly be wonderful.”

    The result came out of a long-running interdisciplinary collaboration between Nelson’s research group and that of Gang Chen, the Carl Richard Soderberg Professor of Mechanical Engineering and Power Engineering. MIT co-authors on the paper are lead authors Sam Huberman and Ryan Duncan, Ke Chen, Bai Song, Vazrik Chiloyan, Zhiwei Ding, and Alexei Maznev.

    “In the express lane”

    Normally, heat travels through crystals in a diffusive manner, carried by “phonons,” or packets of acoustic vibrational energy. The microscopic structure of any crystalline solid is a lattice of atoms that vibrate as heat moves through the material. These lattice vibrations, the phonons, ultimately carry heat away, diffusing it from its source, though that source remains the warmest region, much like a kettle gradually cooling on a stove.

    The kettle remains the warmest spot because as heat is carried away by molecules in the air, these molecules are constantly scattered in every direction, including back toward the kettle. This “back-scattering” occurs for phonons as well, keeping the original heated region of a solid the warmest spot even as heat diffuses away.

    However, in materials that exhibit second sound, this back-scattering is heavily suppressed. Phonons instead conserve momentum and hurtle away en masse, and the heat stored in the phonons is carried as a wave. Thus, the point that was originally heated is almost instantly cooled, at close to the speed of sound.

    Previous theoretical work in Chen’s group had suggested that, within a range of temperatures, phonons in graphene may interact predominately in a momentum-conserving fashion, indicating that graphene may exhibit second sound. Last year, Huberman, a member of Chen’s lab, was curious whether this might be true for more commonplace materials like graphite.

    Building upon tools previously developed in Chen’s group for graphene, he developed an intricate model to numerically simulate the transport of phonons in a sample of graphite. For each phonon, he kept track of every possible scattering event that could take place with every other phonon, based upon their direction and energy. He ran the simulations over a range of temperatures, from 50 K to room temperature, and found that heat might flow in a manner similar to second sound at temperatures between 80 and 120 K.

    Huberman had been collaborating with Duncan, in Nelson’s group, on another project. When he shared his predictions with Duncan, the experimentalist decided to put Huberman’s calculations to the test.

    “This was an amazing collaboration,” Chen says. “Ryan basically dropped everything to do this experiment, in a very short time.”

    “We were really in the express lane with this,” Duncan adds.

    Upending the norm

    Duncan’s experiment centered around a small, 10-square-millimeter sample of commercially available graphite.

    Using a technique called transient thermal grating, he crossed two laser beams so that the interference of their light generated a “ripple” pattern on the surface of a small sample of graphite. The regions of the sample underlying the ripple’s crests were heated, while those that corresponded to the ripple’s troughs remained unheated. The distance between crests was about 10 microns.

    Duncan then shone onto the sample a third laser beam, whose light was diffracted by the ripple, and its signal was measured by a photodetector. This signal was proportional to the height of the ripple pattern, which depended on how much hotter the crests were than the troughs. In this way, Duncan could track how heat flowed across the sample over time.

    If heat were to flow normally in the sample, Duncan would have seen the surface ripples slowly diminish as heat moved from crests to troughs, washing the ripple pattern away. Instead, he observed “a totally different behavior” at 120 K.

    Rather than seeing the crests gradually decay to the same level as the troughs as they cooled, the crests actually became cooler than the troughs, so that the ripple pattern was inverted — meaning that for some of the time, heat actually flowed from cooler regions into warmer regions.

    “That’s completely contrary to our everyday experience, and to thermal transport in almost every material at any temperature,” Duncan says. “This really looked like second sound. When I saw this I had to sit down for five minutes, and I said to myself, ‘This cannot be real.’ But I ran the experiment overnight to see if it happened again, and it proved to be very reproducible.”

    According to Huberman’s predictions, graphite’s two-dimensional relative, graphene, may also exhibit properties of second sound at even higher temperatures approaching or exceeding room temperature. If this is the case, which they plan to test, then graphene may be a practical option for cooling ever-denser microelectronic devices.

    “This is one of a small number of career highlights that I would look to, where results really upend the way you normally think about something,” Nelson says. “It’s made more exciting by the fact that, depending on where it goes from here, there could be interesting applications in the future. There’s no question from a fundamental point of view, it’s really unusual and exciting.”

    This research was funded in part by the Office of Naval Research, the Department of Energy, and the National Science Foundation.

    See the full article here .


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    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

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  • richardmitnick 12:25 pm on March 15, 2019 Permalink | Reply
    Tags: "New state of matter discovered that could lead to better quantum engineering", , , Catch and visualize electrons in a high-temperature iron-based superconducting material which interact as a new state of matter not observed in equilibrium, Laser Technology, University of Alabama Birmingham   

    From University of Alabama Birmingham: “New state of matter discovered that could lead to better quantum engineering” 

    From University of Alabama Birmingham

    March 05, 2019
    Alicia Rohan

    1
    Ames Laboratory researchers used laser pulses of less than a trillionth of a second in much the same way as flash photography, in order to take a series of snapshots. Called terahertz spectroscopy, this technique can be thought of as “laser strobe photography” where many quick images reveal the subtle movement of electron pairings inside the materials using long wavelength far-infrared light. Credit: US Department of Energy, Ames Laboratory

    A team of experimentalists at the U.S. Department of Energy’s Ames Laboratory and theoreticians at University of Alabama Birmingham discovered a remarkably long-lived new state of matter in an iron pnictide superconductor, which reveals a laser-induced formation of collective behaviors that compete with superconductivity.

    Using intense lasers with extremely short pulses in a way equivalent to strobe photography, theoretical and computational physicists at the University of Alabama at Birmingham collaborated with experimentalists at Ames National Lab and Iowa State University to catch and visualize electrons in a high-temperature iron-based superconducting material, which interact as a new state of matter not observed in equilibrium.

    Switching on this state of matter with its unusual, quantum properties takes intense laser pulses, like a flash, hitting the cooled superconductor. Then, a second light pulse triggers an ultrafast camera to take images of this state and observe collective behaviors competing with superconductivity that, when fully understood and tuned, could one day have implications for faster, heat-free, quantum computing, information storage and communication — or what is called “quantum engineering.”

    “The discovery of this new switching scheme and quantum state was full of challenges,” said Ilias Perakis, Ph.D., chair of the UAB College of Arts and Sciences Department of Physics. “To find new emergent electron matter beyond solids, liquids and gases, today’s condensed matter physicists can no longer fully rely on traditional, slow, thermodynamic tuning knobs such as changing temperatures, pressures, chemical compositions or magnetic fields.”

    The UAB advanced computation team of postdoctoral research fellow Martin Mootz, Ph.D., and Perakis developed a model and simulations that made it possible for Jigang Wang’s laser spectroscopy group at Iowa State University and the United States Department of Energy’s Ames Laboratory to identify the experimental signatures of the new quantum state. The experimental signatures were driven by intense laser excitation and are not observed in equilibrium.
    Conducting electricity without resistance

    The new switching scheme developed by this collaboration uses short pulsed light particles to selectively bombard the superconductor energy gap for less than a trillionth of a second. This suddenly switches the superconductor, which at ultracold temperatures can conduct electricity without resistance, to a state of matter not observed under equilibrium conditions.

    The scientific journal Physical Review Letters recently published a paper describing this discovery. This paper follows a recent publication in the journal Nature Materials and is part of an ongoing project funded by the U.S. Department of Energy. In most cases, exotic states of matter such as the one described in this research paper are unstable and short-lived. In this case, the state of matter is metastable, or without decay to a stable state for an order of magnitude longer than conventional equilibration pathways.

    A remaining challenge for the researchers is to figure out how to control and further stabilize the hidden state, and whether this is suitable for the implementation, for example, of quantum logic operations. That could enable researchers to apply and even harness coherence and dynamics of the hidden state for practical functions — such as quantum computing — and for fundamental tests of bizarre quantum mechanics phenomena now used for “quantum engineering.”

    “We aim to create a sustainable innovation and entrepreneurship ecosystem in Birmingham, powered by UAB research and education on advanced materials and computation, and necessary for enabling the ‘Silicon Valley of the South’ sometime in the near future,” Perakis said. “Today, almost all technologies that underpin the global economy and health care depend on advanced materials and computation, in one way or the other.”
    Engine of progress

    Perakis states that the discovery and understanding of new quantum materials with unique properties is an engine of progress for Birmingham and the nation as a whole. Demand for novel materials designed to respond in desired ways under extreme conditions and external stimuli is rapidly rising for applications in key technologies and industries.

    For example, the very recent launch of a National Quantum Initiative by President Donald Trump and Congress recognizes that multifunctional devices based on “quantum phenomena” will be an engine for future economic growth. Quantum phenomena are already being incorporated into technologies for next-generation computers, sensors and detectors that demonstrate superior performance characteristics.

    Quantum device capabilities envisioned include enhanced resolution in imaging, sensors and detectors; advanced cryptography for more secure communication; and significantly larger computational capabilities at speeds far greater than those possible at present. These and other advances require a more detailed interdisciplinary effort to understand how materials behave under extreme and non-equilibrium conditions. This is the focus of the UAB Department of Physics, supported by a grant from the U.S. Department of Energy and others.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    The University of Alabama at Birmingham (UAB) is a public research university in Birmingham, Alabama. Developed from an academic extension center established in 1936, the institution became a four-year campus in 1966 and a fully autonomous institution in 1969. Today, it is one of three institutions in the University of Alabama System and, along with the University of Alabama, an R1 research institution. In the fall of 2015, 19,656 students from more than 110 countries were enrolled at UAB pursuing studies in 140 programs of study in 12 academic divisions leading to bachelor’s, master’s, doctoral, and professional degrees in the social and behavioral sciences, the liberal arts, business, education, engineering, and health-related fields such as medicine, dentistry, optometry, nursing, and public health.

    The UAB Health System, one of the largest academic medical centers in the United States, is affiliated with the university. UAB Hospital sponsors residency programs in medical specialties, including internal medicine, neurology, surgery, radiology, and anesthesiology. UAB Hospital is the only Level I trauma center in Alabama.

    UAB is the state’s largest employer, with more than 21,000 faculty and staff and over 53,000 jobs at the university and in the health system. An estimated 10 percent of the jobs in the Birmingham-Hoover Metropolitan Area and 1 in 33 jobs in the state of Alabama are directly or indirectly related to UAB. The university’s overall annual economic impact was estimated to be $4.6 billion in 2010.

     
  • richardmitnick 4:58 pm on March 2, 2019 Permalink | Reply
    Tags: , , , , , , Laser Technology, So many recent successes for NASA ansd ESA it is astounding great science,   

    From SPIE: “Lasers make the grade in Earth observation and space exploration” 

    SPIE

    From SPIE

    1 March 2019
    Mike Hatcher

    Astronomers, weather forecasters, and Earth scientists are among those now benefiting from the application of solid-state lasers in space.

    1
    Laser equipment for cooling atoms in space arrived at the International Space Station in July 2018 on board a Cygnus supply vehicle – seen here being collected by robotic arm. Photo: NASA.

    Even by stellar historic standards, it has been a remarkable few months for space probes and their on-board optical instrumentation. Late 2018 saw the erstwhile Voyager 2 probe – complete with interferometer, ultraviolet spectrometer, photo-polarimeter, and dual-camera imaging science system – finally leave the solar system.

    NASA/Voyager 2

    We’ve also witnessed some extraordinary imagery and data acquisition carried out by missions such as the Parker Solar Probe, the close encounter between OSIRIS-REx and asteroid Bennu, and ozone monitoring by the Earth-observing Sentinel-5P satellite.

    NASA Parker Solar Probe Plus named to honor Pioneering Physicist Eugene Parker

    NASA OSIRIS-REx Spacecraft

    ESA Copernicus Sentinel-5P

    Just weeks before Photonics West opened its doors the imaging instruments on NASA’s New Horizons mission captured the unusual “lumpy snowman” form of Ultima Thule, and a couple of days later China’s Chang’e 4 probe touched down on the far side of the Moon.

    NASA/New Horizons spacecraft

    China’s Chang’e 4 moon lander

    Recent months have also seen the launch of the Bepi Colombo mission to Mercury, its payload featuring a laser altimeter and an ultraviolet (UV) spectroscopy probe, a laser-cooled atom experiment delivered to the International Space Station (ISS), and the deployment of laser terminals to quickly transmit huge data sets back to Earth from imaging satellites.

    ESA-JAXA BepiColombo

    In terms of photonics equipment, perhaps most satisfying of all has been the recent arrival of a couple of solid-state lasers on board Earth-orbiting spacecraft. Last August, the European Space Agency (ESA) finally launched its wind-monitoring Aeolus satellite.

    ESA ADM-Aeolus satellite

    The first wind lidar instrument in space, it is based around a UV laser and is set to provide far more accurate and detailed monitoring of wind speeds than was previously possible.

    Attempts to understand and forecast the wind date back as far as Aristotle in the 4th century BC. Today, wind profiles sampled down through the atmosphere are needed for accurate medium- to long-term weather forecasting, and are critical for modelling climate change. But until Aeolus, this information was not available from direct measurement: the best equivalent came from ground sensors and balloon monitors giving localized point measurements, followed by extrapolation through cloud tracking or computer simulations. Aeolus being in orbit changes that, and for the first time global wind fields can be mapped directly, in three dimensions.

    Challenging development

    “Using revolutionary laser technology, Aeolus will measure winds around the globe and play a key role in our quest to better understand the workings of our atmosphere,” announced ESA following the launch of the 1.4-tonne satellite aboard a Vega rocket last year. “Importantly, this novel mission will also improve weather forecasting.”

    But the mission has also proved to be one of ESA’s most technologically demanding. Problems with the “Aladin” UV laser, in particular the damage caused to its system optics over an extended operating period, had delayed the original launch schedule by more than a decade. Thanks in part to technical breakthroughs made with a similar source – the green laser at the heart of NASA’s similarly delayed ICESat-2 mission – the Aeolus mission now looks set for major success.

    NASA ICESat 2

    A couple of weeks after launch, Aeolus sent back its first data, and in November Errico Armandillo, the retired head of ESA’s optoelectronics section, reflected on the development. “Today Aeolus is returning more wind data than all ground-based measuring systems put together,” he remarked. “But it took the sustained efforts of ESA labs and technical experts – in close cooperation with the Aeolus team – to make it fly.”

    In fact ESA set up two new laboratories to solve its laser issues. It called in additional support from the German Aerospace Center to produce entirely new technical standards, which are now being applied to all subsequent laser missions.

    “The commercial space industry by itself could not have gone to the lengths we took,” Armandillo pointed out.

    The idea of flying a wind-surveying lidar in orbit was nothing new. In fact it had been explored as long ago as the early 1980s, considered at one time for the ISS. And in fact the technology developed back then is now used to help guide rendezvous and docking operations with ISS-supplying cargo spacecraft.

    Initially a high-energy carbon dioxide gas laser was earmarked for the lidar role, before the mid- 1990s development of space-worthy pump laser diodes opened the door to far more compact solid-state designs. The Aeolus mission was pencilled in for a launch some time after 2000.

    The Aladin laser is at the heart of the Aeolus satellite

    Based around a conventional Nd:YAG solid-state laser crystal, the UV wavelength selected is seen as essential for achieving the high level of back-scatter from both molecular and aerosol components to provide reliable lidar signals. But ESA saw the first signs of trouble in NASA’s ICESat mission, which was using a UV laser to map ice. Around the same time, ground tests on Aladin began to show laser-induced contamination of optics.

    The key problem was then identified: out-gassing of organic molecules from Aladin’s laser equipment was accumulating on system lenses, before being carbonized by the high-energy UV laser pulses. As they grew, those deposits further absorbed the laser’s heat, distorting and darkening the optical components.

    It meant that the original performance of the UV laser within Aladin was nowhere close to requirements. ESA says that when it ran a prototype version of the lidar system, its laser optics degraded by 50% in less than six hours of operations – not much use for a proposed three-year mission.

    “The first solution was to take extreme precautions to remove all organics,” Armandillo said. “But this did not prove entirely possible. Even at just a few parts per billion of organics, contamination was still introduced.”

    For more clues the team approached users of high-energy UV lasers in terrestrial applications. That included working closely with two German optics companies, LaserOptik and LayerTec, as well as experts at France’s Mégajoule facility – where lasers are employed to ignite nuclear fusion reactions – and the semiconductor industry. In principle, the answer proved remarkably simple. Injecting a small amount of oxygen allowed the contamination to burn up under the heat of the laser, in the process cleaning the lens. In tests, the ESA team says it saw this approach work in a matter of minutes.

    Laser breathing

    Rather than redesigning Aladin to work on a fully pressurized basis, small amounts of oxygen are released from a pair of 30-liter tanks. The oxygen gas flows close to the optical surfaces that are exposed to the UV laser, and gradually leaks out of the instrument enclosure.

    “Just like us, the laser has to breathe,” explained laser engineer Linda Mondin in a report by ESA. “It’s very elegant because the burnt-up contaminants flow out of the instrument along with this oxygen, in the form of carbon dioxide and water.” Only 25 Pascals of residual oxygen pressure is needed – just one four-thousandth of standard atmospheric pressure.

    Though contamination was the key issue facing the Aladin team, it was far from the only problem. Heat produced within the volume of the laser transmitter also needed removal. This was solved using ‘heat pipes’, which cool the laser by evaporating liquid and moving it to a space-facing radiator.

    Solving the various problems has ultimately created new technology that is set to benefit a range of future missions. Aladin’s development has yielded ESA some world-leading optics and optoelectronics capability, along with a set of ISO-certified laser development standards for other laser-based missions – starting with the “EarthCARE” mission for clouds and aerosol monitoring.

    ESA/JAXA EarthCARE satellite

    Pencilled in for launch in 2021, this will carry an atmospheric lidar instrument based around a 355 nm laser source to profile aerosols and thin clouds.

    “It’s proved an extremely complex mission, and we’ve learnt an awful lot about lasers,” concluded Rondin, with Aeolus’s instrument manager Denny Wernham adding: “The fact we have a high-power UV laser instrument now working in space is testament to all of the hard work, ingenuity, and inventiveness of many dedicated engineers in industry, ESA, and elsewhere.

    “Aeolus is a world-first mission that will hopefully lead to many active laser missions in the future, and shows the true value of close collaboration between industry and ESA to find innovative solutions to very tough technical challenges.”

    “There were so many ways it could go wrong, we were worried,” recalled Armandillo following the 2018 launch. “And then it worked! Those first wind profiles felt like Christmas coming early, a really amazing gift.”

    ICESat-2 [above]: up and running
    Just as Aeolus and its Aladin laser were starting to return those initial wind profiles from space, NASA launched its ‘ICESat-2′ satellite from California’s Vandenberg Air Force Base.

    Like Aeolus, the mission – comprising a single-instrument laser altimeter payload – was delayed and significantly over its original budget. But it has now deployed its Advanced Topographic Laser Altimeter System (ATLAS), flying in a polar orbit at an average altitude of 290 miles.

    ATLAS – Advanced Topographic Laser Altimeter System by Newton LLC

    Its job is to monitor annual changes in the height of the Greenland and Antarctic ice sheets, to a precision of just 4 mm.

    Developed by the Virginia-based photonics and engineering services company Fibertek, the two flight lasers aboard ICESat-2 emit millijoule-scale nanosecond pulses at 532 nm and a repetition rate of 10 kHz. In continuous operation over the three years of the mission, that equates to around a trillion pulses in all – with Fibertek saying that the tough performance metrics represented a significant increase in the complexity and reliability requirements for a space-based laser system.

    The optical design of ATLAS splits the laser source into three separate pairs of beams that are fired towards Earth at different angles, such that at ground level there is a 3.3 km gap between the beam pairs. This contrasts with the approach used on the original ICESat mission that flew between 2003 and 2009 but whose laser only operated at 40 Hz, and provides much denser cross-track sampling.

    For Earth scientists and studies of climate change, the altimeter should yield a height measurement every 70 cm along the orbiting track, with Fibertek saying that elevation estimates in sloped areas and rough surfaces around crevasses will be much improved.

    According to the ICESat-2 team, only about a dozen of the approximately 20 trillion photons that leave ATLAS with each laser pulse return to the satellite’s telescope after a round trip that takes around 3.3 milliseconds. To detect those scarce returning photons, the system is equipped with a 76 cm-diameter beryllium telescope. A series of filters ensures that only light of precisely 532 nm reaches the detectors, eliminating any reflected sunlight that might influence the results.

    The ATLAS laser, part of NASA’s much-delayed ICESat-2 mission, was launched in September 2018. It will provide high-precision profiles of ice sheets and sea ice for climate studies. Photo by NASA

    Just three months after launch, ICESat-2 was already exceeding scientists’ expectations. NASA said that the satellite had measured the height of sea ice to within an inch, traced the terrain of previously unmapped Antarctic valleys, surveyed remote ice sheets, and peered through forest canopies and shallow coastal waters.

    “ICESat-2 is going to be a fantastic tool for research and discovery, both for cryospheric sciences and other disciplines,” said Tom Neumann, ICESat-2 project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Neumann and others shared the first results from the mission at the American Geophysical Union’s December 2018 meeting in Washington, DC.

    “It’s spectacular terrain,” reported Benjamin Smith, a glaciologist with the University of Washington, Seattle, and member of the ICESat-2 science team. “We’re able to measure slopes that are steeper than 45 degrees, and maybe even more, all through this [Transantarctic] mountain range.”

    The returning photons have shown high ice plateaus, crevasses in the ice 65 feet deep, and the sharp edges of ice shelves dropping into the ocean. Those first measurements will help fill in current gaps in maps of the Antarctic, Smith said, although the most critical science of the ICESat-2 mission is yet to come. As researchers refine their knowledge of exactly where the instrument is pointing, they can start to measure the rise or fall of ice sheets and glaciers.

    “Very soon, we’ll have measurements that we can compare to older measurements of surface elevation,” Smith said. “And after the satellite’s been up for a year, we’ll start to be able to watch the ice sheets change over the seasons.”

    Cold Atom Lab

    Cold Atom Lab NASA JPL

    Cold Atom Lab NASA JPL II

    Not long before the launch of the Aeolus and ICESat-2 sources, another laser system made its way to the ISS, where it is now carrying out quantum research inside the orbiting Cold Atom Lab (CAL). Part of a scientific payload that arrived in May 2018, it is based around commercial laser equipment and capable of trapping potassium and rubidium isotopes.

    By July, the space lab had produced Bose-Einstein condensates (BECs) of rubidium atoms in orbit for the first time, controlled by scientists on the ground at NASA’s Jet Propulsion Laboratory (JPL) in California. Robert Thompson, CAL project scientist and a physicist at JPL, said at the time. “It’s been a long, hard road to get here, but completely worth the struggle, because there’s so much we’re going to be able to do with this facility.”

    Although shrinking the BEC-making equipment to the size demanded for launch to the ISS has been a huge challenge, the advantages of the environment are enormous, from the point of view of quantum experimentation. Unlike on Earth, the persistent microgravity allows scientists to observe individual BECs for 5-10 seconds at a time, and to repeat measurements for up to six hours every day.

    In fact this was not quite the first cold atom experiment in space. In January 2017 the “MAIUS-1” sounding rocket launched a diode laser system for laser cooling and rubidium atom interferometry to an altitude of 243 kilometers, before returning to the ground.

    Maius-1 Payload Johannes Gutenberg Universitaet Mainz

    Developed by Humboldt University Berlin’s optical metrology research group, initial results confirmed that it was possible to carry out research on laser-cooled atoms in space, and in November 2018 the German consortium reported that it had carried out a remarkable 110 experiments on BECs during the six minutes of space travel that were possible.

    Another diode-pumped solid-state laser currently traversing the solar system sits inside an altimeter setup destined for the planet Mercury. Launched by the ESA in October, the Bepi Colombo probe is a collaboration with the Japan Aerospace Exploration Agency (JAXA).

    Designed and built by a Swiss-German-Spanish team led by engineers at the University of Bern, the altimeter kit will be used to map Mercury’s topography and surface morphology in unprecedented detail, and is said to be the first such instrument developed for a European interplanetary mission. Based around a Q-switched, nanosecond-pulsed Nd:YAG source operating at 10 Hz, it will fire relatively high-energy (50 mJ) bursts of 1064 nm light at the planet, and collect reflections from the surface around 5 ms later using a silicon avalanche photodiode, via a narrowband filter.

    Elsewhere in the solar system, NASA’s OSIRIS-REx mission has just completed its approach to the asteroid Bennu, where it is now in close orbit. Ultimately, it is set to grab a sample from the surface of the orbiting rock and bring it back to Earth, but before that Bennu had to be mapped in considerable detail to ensure that the spacecraft could be maneuvered into exactly the right orbit to achieve the close fly-by.

    That operation relied on another laser altimeter featuring a lidar scanner, to generate a detailed three-dimensional map of Bennu’s shape. Built by the Canadian Space Agency, it will help the OSIRIS-REx team identify the best location from which to grab a sample. Two lasers are on board: a high-energy source to scan the asteroid at distances between 7.5 km and 1 km from the surface, and a second low-energy emitter that can be used for rapid time-of-flight imaging down to 225 m.

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    Please help promote STEM in your local schools.

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    See the full article here .

     
  • richardmitnick 9:29 am on February 26, 2019 Permalink | Reply
    Tags: , , , Laser Technology, One might imagine that a “table-top version of CERN” is possible, Plasma wakefields, Proton beams, Wakefield acceleration   

    From “Physics”: “Viewpoint: Shooting Ahead with Wakefield Acceleration” 

    Physics LogoAbout Physics

    Physics Logo 2

    From Physics

    February 25, 2019
    Florian Grüner
    University of Hamburg
    Center for Free-Electron Laser Science, Hamburg, Germany

    A method for accelerating particles, called wakefield acceleration, has notched up its output energy, bringing it closer to its goal of shrinking the size of accelerator facilities.

    1
    APS/Alan Stonebraker
    Figure 1: Wakefield acceleration can use different drivers. In the laser-driven case (top), a strong laser pulse is fired into a preformed plasma. The pulse induces charge separation in the plasma, and the electric field from this charge configuration can accelerate trapped electrons. In the proton-driven scenario (bottom), a high-energy proton bunch is sent into a gas. A relatively weak laser pulse ionizes the gas at the mid-point of the bunch, leading to a modulation of the bunch’s tail. The resulting microbunches can accelerate electrons injected into the stream.

    The field of plasma wakefield acceleration is picking up speed. This method, which was first proposed in 1979 [1], creates a collective motion of plasma particles, generating an accelerating field in its wake. The amplitude of this accelerating field is not limited, as it is in conventional acceleration techniques that use radio frequency pulses. The implication is that wakefield acceleration has the potential to work over much smaller lengths, which would allow a reduction in the size (and cost) of accelerator facilities. There exist different methods for generating wakefields, and now researchers are reporting significant progress for two of these techniques. One method using laser-driven wakefields has generated 8-GeV electrons, a new energy record that doubles the previous record [2]. A different approach, with proton beams as drivers, is not far behind, with recent experiments demonstrating its ability to accelerate electrons up to 2 GeV [3–5]. These are both key achievements, but the goal of having wakefield accelerators will have to wait until researchers gain more control over the output beams.

    What is a plasma wakefield? A helpful analogy is a capacitor, where two oppositely charged parallel plates generate an electric field that can accelerate particles from one plate to the other. In a plasma, a similar field can arise when a “driver,” such as a laser pulse, separates negatively charged electrons from positively charged ions. This charge separation can remain a stable configuration—the so-called wakefield—if the effective size of the driver is less than the plasma wavelength, which characterizes the length for a coherent response to a charge displacement. Inside the wakefield, the electric field—expressed as a voltage gradient—can reach 1 TV/m. By comparison, conventional accelerators can only reach gradients of 100 MV/m before they run the risk of being damaged by electrical discharge.

    If plasma wakefields can have gradients of 1 TV/m, one might imagine that a “table-top version of CERN” is possible. However, there’s a problem. Wakefields are typically driven by a laser pulse, whose speed is significantly reduced inside a plasma. At some point, the electrons will get ahead of the accelerating part of the wakefield, like surfers who outrun the waves they are riding on. There are basically two ways out of this so-called dephasing issue: either one stages several laser-driven plasma accelerator units in succession, or one selects a different driver—a high-energy proton bunch that moves through the plasma at near the speed of light.

    If one chooses to go with the laser-driven strategy, each stage needs to give an energy boost of about 10 GeV [6]. In 2004, researchers obtained the first laser-plasma accelerated electrons with a “nonthermal” energy spectrum peaking at around 100 MeV [7]. Two years later, the peak energy reached 1 GeV [8]. Now, Anthony Gonsalves from Lawrence Berkeley National Laboratory, California, and colleagues have managed to accelerate electrons to 8 GeV with lasers [2], which makes this an important milestone in reaching the needed 10-GeV energy per stage.

    So, why did it take more than 10 years to go from 1 GeV to 8 GeV? One reason is the complexity of these experiments. The first-generation laser-plasma experiments operated with just one laser, which both created the plasma (through gas ionization) and generated the wakefield. The next generation relegated the ionization step to a discharge capillary, which is a gas container that is typically made out of glass, with an inner diameter smaller than that of a human hair. When a strong voltage is applied to the capillary, the discharge ionizes the gas, creating a plasma whose density is lowest along the tube axis, as the walls are cooling faster than the center (Fig. 1, top). This transverse density gradient helps guide the laser pulse over sufficiently long acceleration lengths of around 10 cm. Gonsalves et al. have improved on this design by using a second laser system in addition to the discharge capillary. This second laser acts as a “laser heater,” increasing the transverse plasma density gradient even further—a prerequisite for reaching the 8-GeV level.

    As already mentioned, the laser-driven method will require coordinating multiple stages, a feat that remains to be tackled. The alternative approach is to use a single high-energy proton bunch as a driver. The difficulty here is that the proton bunch is initially much longer than the plasma wavelength, which would normally mean that no stable wakefield can arise. Fortunately, nature provides a solution: proton–plasma interactions cause the proton bunch to spontaneously form a density modulation consisting of “microbunches” whose spacing is roughly that of the plasma wavelength. Stable wakefields arise in between the microbunches (Fig. 1, bottom). To control this so-called self-modulation, researchers can use a laser-induced ionization front that acts as a “seed” for the breakup of the proton bunch.

    Early in 2018, the Advanced Wakefield Experiment (AWAKE) made the first successful demonstration of proton-driven acceleration, using 400-GeV proton bunches from the Super Proton Synchrotron at CERN [3].

    CERN AWAKE schematic


    CERN AWAKE

    The Super Proton Synchrotron (SPS), CERN’s second-largest accelerator. (Image: Julien Ordan/CERN)


    CERN LS2 SPS The new solid-state amplifier system developed by CERN with the Thales Gérac company comprises 32 towers, in which 2560 RF modules, each containing four transistors, will be installed. (Image: Maximilien Brice/CERN)

    The researchers showed that they could achieve a 2-GeV energy boost for electrons that were injected into the wake of these proton bunches. In a pair of follow-up studies published earlier this month [Physical Review Letters], [Nature], the AWAKE Collaboration verified that the roughly 10-cm-long proton bunches break up into microbunches that are about 2 mm long, as predicted for seeded self-modulation [4, 5]. The acceleration occurs over 10 m, which is roughly 100 times longer than the acceleration length in the laser-driven experiment. The longer distance is due to the fact that the proton-bunch experiment requires a lower plasma density and hence a weaker electric field gradient. However, the proton-based scheme may prove better suited than the laser-driven case for accelerating positrons. The positrons could be simply injected into the wake of the proton beam in the same way as electrons are.

    The AWAKE Collaboration and Gonsalves et al. have both achieved landmark results, but much work remains. The CERN approach is aimed at studying the possibilities of a novel high-energy electron-positron collider, while the laser-based method targets not only collider applications but also the driving of hard x-ray free-electron lasers, which are used, for instance, to determine protein structures. It is really difficult to judge which approach is closer to its goal, simply because both methods are still busy demonstrating acceleration. To go to the next step of creating a user facility, wakefield acceleration requires high beam quality and stability, which neither technique has achieved so far.

    We often ask: when was the starting point of a new field? Did lunar exploration, for example, begin with Jules Verne’s 1865 novel about a voyage to the moon, with the first human in space in 1961, or with the moon landing in 1969? For wakefield acceleration, there are several potential starting points. In my view, the “human-in-space” moment for plasma wakefield acceleration took place in 2004 when researchers managed to achieve 100-MeV energies with quasimonochromatic energy spectra. It is still not clear when the “moon landing” will happen in the form of a wakefield-accelerator user facility. The key to reaching this goal will be to develop an unprecedented level of control over all relevant parameters. This means introducing entirely new “knobs” for things like the final energy and energy spread of the accelerated particles.

    References

    T. Tajima and J. M. Dawson, “Laser electron accelerator,” Phys. Rev. Lett. 43, 267 (1979).
    A. J. Golsalves et al., “Petawatt laser guiding and electron beam acceleration to 8 GeV in a laser-heated capillary discharge waveguide,” Phys. Rev. Let 122, 084801 (2019).
    E. Adli et al. (AWAKE Collaboration), “Acceleration of electrons in the plasma wakefield of a proton bunch,” Nature 561, 363 (2018).
    M. Turner et al. (AWAKE Collaboration), “Experimental observation of plasma wakefield growth driven by the seeded self-modulation of a proton bunch,” Phys. Rev. Lett. 122, 054801 (2019).
    E. Adli et al. (AWAKE Collaboration), “Experimental observation of proton bunch modulation in a plasma at varying plasma densities,” Phys. Rev. Lett. 122, 054802 (2019).
    C. B. Schroeder, E. Esarey, C. G. R. Geddes, C. Benedetti, W. P. Leemans et al., “Physics considerations for laser-plasma linear colliders,” Phys. Rev. ST Accel. Beams 13, 101301 (2010).
    C. G. R. Geddes, Cs. Toth, J. van Tilborg, E. Esarey, C. B. Schroeder, D. Bruhwiler, C. Nieter, J. Cary, and W. P. Leemans, “High-quality electron beams from a laser wakefield accelerator using plasma-channel guiding,” Nature 431, 538 (2004); S. P. D. Mangles et al., “Monoenergetic beams of relativistic electrons from intense laser–plasma interactions,” 431, 535 (2004); J. Faure, Y. Glinec, A. Pukhov, S. Kiselev, S. Gordienko, E. Lefebvre, J.-P. Rousseau, F. Burgy, and V. Malka, “A laser–plasma accelerator producing monoenergetic electron beams,” 431, 541 (2004).
    W. P. Leemans, B. Nagler, A. J. Gonsalves, Cs. Tóth, K. Nakamura, C. G. R. Geddes, E. Esarey, C. B. Schroeder, and S. M. Hooker, “GeV electron beams from a centimetre-scale accelerator,” Nat. Phys. 2, 696 (2006).

    See the full article here .

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    Physicists are drowning in a flood of research papers in their own fields and coping with an even larger deluge in other areas of physics. How can an active researcher stay informed about the most important developments in physics? Physics highlights a selection of papers from the Physical Review journals. In consultation with expert scientists, the editors choose these papers for their importance and/or intrinsic interest. To highlight these papers, Physics features three kinds of articles: Viewpoints are commentaries written by active researchers, who are asked to explain the results to physicists in other subfields. Focus stories are written by professional science writers in a journalistic style and are intended to be accessible to students and non-experts. Synopses are brief editor-written summaries. Physics provides a much-needed guide to the best in physics, and we welcome your comments (physics@aps.org).

     
  • richardmitnick 1:47 pm on February 25, 2019 Permalink | Reply
    Tags: "Laser ‘Drill’ Sets a New World Record in Laser-Driven Electron Acceleration", , , , Laser Technology, ,   

    From Lawrence Berkeley National Lab: “Laser ‘Drill’ Sets a New World Record in Laser-Driven Electron Acceleration” 

    Berkeley Logo

    From Lawrence Berkeley National Lab

    February 25, 2019
    Glenn Roberts Jr.
    geroberts@lbl.gov
    (510) 486-5582

    Scientists working at Berkeley Lab’s BELLA Center nearly double their previous record set in 2014.

    LBNL Bella Center during constructon

    1
    This animation shows a plasma channel’s electron density profile (blue) formed inside a sapphire tube (gray) with the combination of an electrical discharge and an 8-nanosecond laser pulse (red, orange, and yellow). Time is shown in nanoseconds. This plasma channel was used to guide femtoseconds-long “driver” laser pulses from the BELLA petawatt laser system, which generated plasma waves and accelerated electrons to 8 billion electron volts in just 20 centimeters. (Credit: Gennadiy Bagdasarov/Keldysh Institute of Applied Mathematics; Anthony Gonsalves/Berkeley Lab)

    Combining a first laser pulse to heat up and “drill” through a plasma, and another to accelerate electrons to incredibly high energies in just tens of centimeters, scientists have nearly doubled the previous record for laser-driven particle acceleration.

    The laser-plasma experiments, conducted at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), are pushing toward more compact and affordable types of particle acceleration to power exotic, high-energy machines – like X-ray free-electron lasers and particle colliders – that could enable researchers to see more clearly at the scale of molecules, atoms, and even subatomic particles.

    The new record of propelling electrons to 7.8 billion electron volts (7.8 GeV) at the Berkeley Lab Laser Accelerator (BELLA) Center surpasses a 4.25 GeV result at BELLA announced in 2014. The latest research is detailed in the Feb. 25 edition of the journal Physical Review Letters. The record result was achieved during the summer of 2018.

    The experiment used incredibly intense and short “driver” laser pulses, each with a peak power of about 850 trillion watts and confined to a pulse length of about 35 quadrillionths of a second (35 femtoseconds). The peak power is equivalent to lighting up about 8.5 trillion 100-watt lightbulbs simultaneously, though the bulbs would be lit for only tens of femtoseconds.

    Each intense driver laser pulse delivered a heavy “kick” that stirred up a wave inside a plasma – a gas that has been heated enough to create charged particles, including electrons. Electrons rode the crest of the plasma wave, like a surfer riding an ocean wave, to reach record-breaking energies within a 20-centimeter-long sapphire tube.

    “Just creating large plasma waves wasn’t enough,” noted Anthony Gonsalves, the lead author of the latest study. “We also needed to create those waves over the full length of the 20-centimeter tube to accelerate the electrons to such high energy.”

    To do this required a plasma channel, which confines a laser pulse in much the same way that a fiber-optic cable channels light. But unlike a conventional optical fiber, a plasma channel can withstand the ultra-intense laser pulses needed to accelerate electrons. In order to form such a plasma channel, you need to make the plasma less dense in the middle.

    3
    Different generations of sapphire tubes, called capillaries, are pictured here. The tubes are used to generate and confine plasmas, and to accelerate electrons. A 20-centimeter capillary setup, similar to the one used in the latest experiments, is pictured at left. (Credit: Marilyn Chung/Berkeley Lab)

    In the 2014 experiment, an electrical discharge was used to create the plasma channel, but to go to higher energies the researchers needed the plasma’s density profile to be deeper – so it is less dense in the middle of the channel. In previous attempts the laser lost its tight focus and damaged the sapphire tube. Gonsalves noted that even the weaker areas of the laser beam’s focus – its so-called “wings” – were strong enough to destroy the sapphire structure with the previous technique.

    Eric Esarey, BELLA Center Director, said the solution to this problem was inspired by an idea from the 1990s to use a laser pulse to heat the plasma and form a channel. This technique has been used in many experiments, including a 2004 Berkeley Lab effort that produced high-quality beams reaching 100 million electron volts (100 MeV).

    Both the 2004 team and the team involved in the latest effort were led by former ATAP and BELLA Center Director Wim Leemans, who is now at the DESY laboratory in Germany. The researchers realized that combining the two methods – and putting a heater beam down the center of the capillary – further deepens and narrows the plasma channel. This provided a path forward to achieving higher-energy beams.

    In the latest experiment, Gonsalves said, “The electrical discharge gave us exquisite control to optimize the plasma conditions for the heater laser pulse. The timing of the electrical discharge, heater pulse, and driver pulse was critical.”

    4
    This animation shows a 3D rendering of plasma waves (blue) excited by a petawatt laser pulse (red) at Berkeley Lab’s BELLA Center as it propagates in a plasma channel. Some of the background electrons are trapped and accelerated to an energy of up to 7.8 GeV in the plasma wave (pink/purple). The simulation was performed on the Edison supercomputer at Berkeley Lab’s National Energy Research Scientific Computing Center. (Credit: Carlo Benedetti/Berkeley Lab)

    The combined technique radically improved the confinement of the laser beam, preserving the intensity and the focus of the driving laser, and confining its spot size, or diameter, to just tens of millionths of a meter as it moved through the plasma tube. This enabled the use of a lower-density plasma and a longer channel. The previous 4.25 GeV record had used a 9-centimeter channel.

    The team needed new numerical models (codes) to develop the technique. A collaboration including Berkeley Lab, the Keldysh Institute of Applied Mathematics in Russia, and the ELI-Beamlines Project in the Czech Republic adapted and integrated several codes. They combined MARPLE and NPINCH, developed at the Keldysh Institute, to simulate the channel formation; and INF&RNO, developed at the BELLA Center, to model the laser-plasma interactions.

    “These codes helped us to see quickly what makes the biggest difference – what are the things that allow you to achieve guiding and acceleration,” said Carlo Benedetti, the lead developer of INF&RNO. Once the codes were shown to agree with the experimental data, it became easier to interpret the experiments, he noted.

    “Now it’s at the point where the simulations can lead and tell us what to do next,” Gonsalves said.

    Benedetti noted that the heavy computations in the codes drew upon the resources of the National Energy Research Scientific Computing Center (NERSC) at Berkeley Lab.

    NERSC

    NERSC Cray Cori II supercomputer at NERSC at LBNL, named after Gerty Cori, the first American woman to win a Nobel Prize in science

    NERSC Hopper Cray XE6 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.

    Future work pushing toward higher-energy acceleration could require far more intensive calculations that approach a regime known as exascale computing.

    “Today, the beams produced could enable the production and capture of positrons,” which are electrons’ positively charged counterparts, said Esarey.

    He noted that there is a goal to reach 10 GeV energies in electron acceleration at BELLA, and future experiments will target this threshold and beyond.

    “In the future, multiple high-energy stages of electron acceleration could be coupled together to realize an electron-positron collider to explore fundamental physics with new precision,” he said.

    Also participating in this research were researchers from UC Berkeley and the National Research Nuclear University in Russia.

    This work was supported by the Department of Energy’s Office of Science, the Alexander von Humboldt Foundation, and the National Science Foundation.

    See the full article here .

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    In the world of science, Lawrence Berkeley National Laboratory (Berkeley Lab) is synonymous with “excellence.” Thirteen Nobel prizes are associated with Berkeley Lab. Seventy Lab scientists are members of the National Academy of Sciences (NAS), one of the highest honors for a scientist in the United States. Thirteen of our scientists have won the National Medal of Science, our nation’s highest award for lifetime achievement in fields of scientific research. Eighteen of our engineers have been elected to the National Academy of Engineering, and three of our scientists have been elected into the Institute of Medicine. In addition, Berkeley Lab has trained thousands of university science and engineering students who are advancing technological innovations across the nation and around the world.

    Berkeley Lab is a member of the national laboratory system supported by the U.S. Department of Energy through its Office of Science. It is managed by the University of California (UC) and is charged with conducting unclassified research across a wide range of scientific disciplines. Located on a 202-acre site in the hills above the UC Berkeley campus that offers spectacular views of the San Francisco Bay, Berkeley Lab employs approximately 3,232 scientists, engineers and support staff. The Lab’s total costs for FY 2014 were $785 million. A recent study estimates the Laboratory’s overall economic impact through direct, indirect and induced spending on the nine counties that make up the San Francisco Bay Area to be nearly $700 million annually. The Lab was also responsible for creating 5,600 jobs locally and 12,000 nationally. The overall economic impact on the national economy is estimated at $1.6 billion a year. Technologies developed at Berkeley Lab have generated billions of dollars in revenues, and thousands of jobs. Savings as a result of Berkeley Lab developments in lighting and windows, and other energy-efficient technologies, have also been in the billions of dollars.

    Berkeley Lab was founded in 1931 by Ernest Orlando Lawrence, a UC Berkeley physicist who won the 1939 Nobel Prize in physics for his invention of the cyclotron, a circular particle accelerator that opened the door to high-energy physics. It was Lawrence’s belief that scientific research is best done through teams of individuals with different fields of expertise, working together. His teamwork concept is a Berkeley Lab legacy that continues today.

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

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  • richardmitnick 4:07 pm on February 24, 2019 Permalink | Reply
    Tags: "Researchers use ‘laser tweezers’ to boost liquid crystal technology", , , Laser Technology, Liquid crystals with their uniform molecular structure and orientation offer exciting possibilities for future technology, , To create the defects in the liquid crystals researchers used laser tweezers—a laser system that can manipulate particles at the nanoscale—to heat up and melt either a tiny point or a line within , , We can keep the defect alive for as long as we want   

    From University of Chicago: “Researchers use ‘laser tweezers’ to boost liquid crystal technology” 

    U Chicago bloc

    From University of Chicago

    Feb 22, 2019
    Emily Ayshford

    1
    Illustration copyright Wikimedia Commons

    Institute for Molecular Engineering breakthrough could lead to new display or sensor technologies.

    Liquid crystals, with their uniform molecular structure and orientation, offer exciting possibilities for future technology.

    They are already the basis of displays, which use the crystals’ orientation to exhibit a wide array of colors. Researchers have wondered whether they could manipulate tiny defects in the crystals to introduce new functions within the liquid—as microchannels for a tiny circuit, or to host chemical reactions, for example. But the first step is to keep the defects stable.

    Researchers with the Institute for Molecular Engineering at the University of Chicago, along with partners at the University of Ljubljana, have shown that by using a combination of flow and light, they can create defects that remain stable in the liquid crystal over long periods of time. The breakthrough, published Feb. 15 in the journal Science Advances, could ultimately result in using liquids in new ways, such as to create new kinds of autonomous materials or nanoscale reactors.

    “For the first time, we can create defects in pure liquids and control them, without introducing anything else into the system,” said Juan de Pablo, the Liew Family Professor in Molecular Engineering at the University of Chicago, who co-authored the research. “It could result in really interesting new objects or materials.”

    To create the defects in the liquid crystals, researchers used laser tweezers—a laser system that can manipulate particles at the nanoscale—to heat up and melt either a tiny point or a line within the material. While the bulk of the liquid crystal remained ordered, the melted spot — several microns in size, just a little smaller than a single red blood cell—became disorganized. As it cooled, the molten liquid becomes reordered, and forms a defect on its trail.

    Because such defects cost the material energy, the material experiences strong driving forces to eliminate them, and it eventually reverts to a uniform, defect-free state.

    But researchers found that if they place the defect into a flow state in a microfluidic device—introducing forces that continually push the defect in different directions—it could not reorient and annihilate itself, and instead remained stable.

    “By doing this, we can keep the defect alive for as long as we want,” said de Pablo, whose pioneering work develops molecular models and advanced computational simulations of molecular and large-scale phenomena.

    Such a system also allowed them to have complete control over the size and shape of the defects. A second laser burst, for example, could break the defect into pieces, or move it from one spot to another.

    To create this system, de Pablo and his group developed computational models of liquid crystals at rest, their defects and the precise forces needed to keep them stabilized. Then the researchers at the University of Ljubljana performed the experiments using this information and theoretical treatments of the underlying materials.

    This system could pave the way for new display or sensor technologies. De Pablo and his collaborators are interested in using this technique to develop complicated networks of microfluidic channels that could serve as miniature factories, with built-in reactors, separation units and transport mechanisms.

    They also are looking to develop autonomous material systems that can stabilize defects on their own using flows. Such a material could “decide” by itself what shape to take in response to external cues, ultimately acting as an integrated system that could perform simple tasks on its own.

    “This technique could have really interesting applications,” de Pablo said. “We have ambitious ideas.”

    Other authors included Rui Zhang, a postdoctoral researcher in de Pablo’s group; and Uroš Tkalec, Tadej Emeršič, Žiga Kos, Simon Čopar and Natan Osterman of the University of Ljubljana.

    See the full article here .

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    An intellectual destination

    One of the world’s premier academic and research institutions, the University of Chicago has driven new ways of thinking since our 1890 founding. Today, UChicago is an intellectual destination that draws inspired scholars to our Hyde Park and international campuses, keeping UChicago at the nexus of ideas that challenge and change the world.

    University of Chicago

    The University of Chicago is an urban research university that has driven new ways of thinking since 1890. Our commitment to free and open inquiry draws inspired scholars to our global campuses, where ideas are born that challenge and change the world.

    We empower individuals to challenge conventional thinking in pursuit of original ideas. Students in the College develop critical, analytic, and writing skills in our rigorous, interdisciplinary core curriculum. Through graduate programs, students test their ideas with UChicago scholars, and become the next generation of leaders in academia, industry, nonprofits, and government.

    UChicago research has led to such breakthroughs as discovering the link between cancer and genetics, establishing revolutionary theories of economics, and developing tools to produce reliably excellent urban schooling. We generate new insights for the benefit of present and future generations with our national and affiliated laboratories: Argonne National Laboratory, Fermi National Accelerator Laboratory, and the Marine Biological Laboratory in Woods Hole, Massachusetts.

    The University of Chicago is enriched by the city we call home. In partnership with our neighbors, we invest in Chicago’s mid-South Side across such areas as health, education, economic growth, and the arts. Together with our medical center, we are the largest private employer on the South Side.

    In all we do, we are driven to dig deeper, push further, and ask bigger questions—and to leverage our knowledge to enrich all human life. Our diverse and creative students and alumni drive innovation, lead international conversations, and make masterpieces. Alumni and faculty, lecturers and postdocs go on to become Nobel laureates, CEOs, university presidents, attorneys general, literary giants, and astronauts.

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

    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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    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 11:20 am on February 15, 2019 Permalink | Reply
    Tags: "Physicists create a quantum refrigerator that cools with an absence of light", , , Laser Technology, Near-field photonic cooling through control of the chemical potential of photons, , , ,   

    From U Michigan via Science Magazine: “Physicists create a quantum refrigerator that cools with an absence of light” 

    U Michigan bloc

    From University of Michigan

    via

    AAAS
    Science Magazine

    Feb. 14, 2019
    Daniel Garisto

    1
    This new device shows that an LED can cool other tiny objects. Joseph Xu/Michigan Engineering, Communications & Marketing

    For decades, atomic physicists have used laser light to slow atoms zinging around in a gas, cooling them to just above absolute zero to study their weird quantum properties. Now, a team of scientists has managed to similarly cool an object—but with the absence of light rather than its presence. The technique, which has never before been experimentally shown, might someday be used to chill the components in microelectronics.

    In an ordinary laser cooling experiment, physicists shine laser light from opposite directions—up, down, left, right, front, back—on a puff of gas such as rubidium. They tune the lasers precisely, so that if an atom moves toward one of them, it absorbs a photon and gets a gentle push back toward the center. Set it up just right and the light saps away the atoms’ kinetic energy, cooling the gas to a very low temperature.

    But Pramod Reddy, an applied physicist at the University of Michigan in Ann Arbor, wanted to try cooling without the special properties of laser light. He and colleagues started with a widget made of semiconducting material commonly found in video screens—a light-emitting diode (LED). An LED exploits a quantum mechanical effect to turn electrical energy into light. Roughly speaking, the LED acts like a little ramp for electrons. Apply a voltage in the right direction and it pushes electrons up and over the ramp, like kids on skateboards. As electrons fall over the ramp to a lower energy state, they emit photons.

    Crucially for the experiment, the LED emits no light when the voltage is reversed, as the electrons cannot go over the ramp in the opposite direction. In fact, reversing the voltage also suppresses the device’s infrared radiation—the broad spectrum of light (including heat) that you see when you look at a hot object through night vision goggles.

    That effectively makes the device colder—and it means the little thing can work like a microscopic refrigerator, Reddy says. All that’s necessary is to put it close enough to another tiny object, he says. “If you take a hot object and a cold object … you can have a radiative exchange of heat,” Reddy says. To prove that they could use an LED to cool, the scientists placed one just tens of nanometers—the width of a couple hundred atoms—away from a heat-measuring device called a calorimeter. That was close enough to increase the transfer of photons between the two objects, due to a process called quantum tunneling. Essentially, the gap was so small that photons could sometimes hop over it.

    The cooler LED absorbed more photons from the calorimeter than it gave back to it, wicking heat away from the calorimeter and lowering its temperature by a ten-thousandth of a degree Celsius, Reddy and colleagues report this week in Nature. That’s a small change, but given the tiny size of the LED, it equals an energy flux of 6 watts per square meter. For comparison, the sun provides about 1000 watts per square meter. Reddy and his colleagues believe they could someday increase the cooling flux up to that strength by reducing the gap size and siphoning away the heat that builds up in the LED.

    The technique probably won’t replace traditional refrigeration techniques or be able to cool materials below temperatures of about 60 K. But it has the potential to someday be used for cooling microelectronics, according to Shanhui Fan, a theoretical physicist at Stanford University in Palo Alto, California, who was not involved with the work. In earlier work, Fan used computer modeling to predict that an LED could have a sizeable cooling effect if placed nanometers from another object. Now, he said, Reddy and his team have realized that idea experimentally.

    See the full article here .


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

    Please support STEM education in your local school system

    Stem Education Coalition

    U MIchigan Campus

    The University of Michigan (U-M, UM, UMich, or U of M), frequently referred to simply as Michigan, is a public research university located in Ann Arbor, Michigan, United States. Originally, founded in 1817 in Detroit as the Catholepistemiad, or University of Michigania, 20 years before the Michigan Territory officially became a state, the University of Michigan is the state’s oldest university. The university moved to Ann Arbor in 1837 onto 40 acres (16 ha) of what is now known as Central Campus. Since its establishment in Ann Arbor, the university campus has expanded to include more than 584 major buildings with a combined area of more than 34 million gross square feet (781 acres or 3.16 km²), and has two satellite campuses located in Flint and Dearborn. The University was one of the founding members of the Association of American Universities.

    Considered one of the foremost research universities in the United States,[7] the university has very high research activity and its comprehensive graduate program offers doctoral degrees in the humanities, social sciences, and STEM fields (Science, Technology, Engineering and Mathematics) as well as professional degrees in business, medicine, law, pharmacy, nursing, social work and dentistry. Michigan’s body of living alumni (as of 2012) comprises more than 500,000. Besides academic life, Michigan’s athletic teams compete in Division I of the NCAA and are collectively known as the Wolverines. They are members of the Big Ten Conference.

     
  • richardmitnick 3:16 pm on February 13, 2019 Permalink | Reply
    Tags: “Pump” light, Laser Technology, Optics and photonics research, Quantum dot lasers, ,   

    From University of Utah: “New phenomenon discovered that fixes a common problem in lasers: Wavelength splitting” 

    From University of Utah

    Feb 7, 2019
    Lisa PotterScience writer,
    University Marketing and Communications
    Office: 801-585-3093
    Mobile: 949-533-7899
    lisa.potter@utah.edu

    A team led by University of Utah physicists has discovered how to fix a major problem that occurs in lasers made from a new type of material called quantum dots. The never-before-seen phenomenon will be important for an emerging field of photonics research, including one day making micro-chips that code information using light instead of electrons.

    Laser wave length spliting U Utah

    The study published on Feb. 4, 2019, in the journal Nature Communications.

    Lasers are devices that amplify light, often producing a single, narrow beam of light. The strength of the beam depends on the material with which the laser was built; light passes through the material, which produces a beam made of light waves all with similar wavelengths, concentrating a lot of energy into a small area. This material property to be able to amplify the beam’s energy is called “gain.”

    Many scientists are building lasers with quantum dots. Quantum dots are tiny crystals of semiconductor materials grown to sizes of only about 100-atoms across. The size of the crystals determines the light beam’s wavelength, from blue light to red light and even into the infrared.

    People are interested in quantum dot lasers because they can tune properties simply by growing the crystals in different sizes by using different semiconducting materials and choosing different shapes and sizes of the lasers. The downside is that quantum dot lasers often contain miniscule defects that split the light into multiple wavelengths, which distributes the beam’s energy and makes it less powerful. Ideally, you want the laser to concentrate the power into one wavelength.

    The new study sought to correct this defect. First, collaborators from the Georgia Institute of Technology made 50 microscopic disk-shaped quantum dot lasers out of cadmium selenide. The U team then showed that that almost all of the individual lasers had defects that split the wavelengths of beams.

    The researchers then coupled two lasers together to correct the wavelength splitting. They put one laser at full gain, which describes the maximum amount of energy possible. To achieve full gain, the scientists shined a green light, called the pump light, onto the first laser. The quantum dot material absorbed the light and re-emitted a more powerful beam of red light. The stronger the green light they shined on the laser, the higher the gain in energy. When the second laser had no gain, the difference between the two lasers prevented any interaction, and splitting still occurred. However, when the team shined a green light onto the second laser, its gain increased, closing the gain difference between the two lasers. Once the gain in the two lasers became similar the interaction between the two lasers corrected the splitting and focused the energy into a single wavelength. This is the first time anyone has observed this phenomenon.

    The findings have implications for a new field, called optics and photonics research. In the past 30 years, researchers have been experimenting with using light to carry information, rather than electrons used in traditional electronics. For example, rather than putting lots of electrons on a microchip to make a computer run, some envision using light instead. Lasers would be a big part of that and the to correct wavelength splitting can provide a significant benefit to controlling information through light. It could also be a major advantage to use materials such as quantum dots in this field.

    “It’s not impossible that someone could make a defect-free laser with quantum dots, but it would be expensive and time-consuming. In comparison, coupling is a quicker, more flexible, cost-effective way to correct the problem,” said Evan Lafalce, research assistant professor of physics and astronomy at the U and lead author of the study. “This is a trick so that we don’t have to make perfect quantum dot lasers.”

    Authors who contributed to the study include Qingji Zeng and Valy Z. Vardeny from the Department of Physics & Astronomy at the University of Utah and Chun Hao Lin, Marcus J. Smith, Sidney T. Malak, Jaehan Jung, Young Jun Yoon, Zhiqun Lin and Vladmir V. Tsukruk from the School of Materials Science and Engineering at the Georgia Institute of Technology. Smith also holds a position at the Air Force Research Laboratory at Wright-Patterson Air Force Base and Jung holds a position at Hongik University.

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    The University of Utah (also referred to as the U, the U of U, or Utah) is a public coeducational space-grant research university in Salt Lake City, Utah, United States. As the state’s flagship university, the university offers more than 100 undergraduate majors and more than 92 graduate degree programs. The university is classified in the highest ranking: “R-1: Doctoral Universities – Highest Research Activity” by the Carnegie Classification of Institutions of Higher Education. The Carnegie Classification also considers the university as “selective”, which is its second most selective admissions category. Graduate studies include the S.J. Quinney College of Law and the School of Medicine, Utah’s only medical school. As of Fall 2015, there are 23,909 undergraduate students and 7,764 graduate students, for an enrollment total of 31,673.

    The university was established in 1850 as the University of Deseret (Listeni/dɛz.əˈrɛt./[12]) by the General Assembly of the provisional State of Deseret, making it Utah’s oldest institution of higher education.It received its current name in 1892, four years before Utah attained statehood, and moved to its current location in 1900.

    The university ranks among the top 50 U.S. universities by total research expenditures with over $486 million spent in 2014. 22 Rhodes Scholars,[14] three Nobel Prize winners, two Turing Award winners, three MacArthur Fellows, various Pulitzer Prize winners, two astronauts, Gates Cambridge Scholars, and Churchill Scholars have been affiliated with the university as students, researchers, or faculty members in its history. In addition, the university’s Honors College has been reviewed among 50 leading national Honors Colleges in the U.S. The university has also been ranked the 12th most ideologically diverse university in the country.

     
  • richardmitnick 10:32 am on February 9, 2019 Permalink | Reply
    Tags: Condenced-Matter Physics, Laser Technology, , , ,   

    From SLAC National Accelerator Lab: “First direct view of an electron’s short, speedy trip across a border” 

    From SLAC National Accelerator Lab

    February 8, 2019
    Glennda Chui

    1
    Electrons traveling between two layers of atomically thin material give off tiny bursts of electromagnetic waves in the terahertz spectral range. This glow, shown in red and blue, allowed researchers at SLAC and Stanford to observe and track the electrons’ ultrafast movements. (Greg Stewart/SLAC National Accelerator Laboratory)

    Watching electrons sprint between atomically thin layers of material will shed light on the fundamental workings of semiconductors, solar cells and other key technologies.

    Electrons flowing across the boundary between two materials are the foundation of many key technologies, from flash memories to batteries and solar cells. Now researchers have directly observed and clocked these tiny cross-border movements for the first time, watching as electrons raced seven-tenths of a nanometer – about the width of seven hydrogen atoms – in 100 millionths of a billionth of a second.

    Led by scientists at the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University, the team made these observations by measuring tiny bursts of electromagnetic waves given off by the traveling electrons – a phenomenon described more than a century ago by Maxwell’s equations, but only now applied to this important measurement.

    “To make something useful, generally you need to put different materials together and transfer charge or heat or light between them,” said Eric Yue Ma, a postdoctoral researcher in the laboratory of SLAC/Stanford Professor Tony Heinz and lead author of a report in Science Advances.

    “This opens up a new way to measure how charge – in this case, electrons and holes – travels across the abrupt interface between two materials,” he said. “It doesn’t just apply to layered materials. For instance, it can also be used to look at electrons flowing between a solid surface and molecules that are attached to it, or even, in principle, between a liquid and a solid.”

    Too short, too fast – or were they?

    The materials used in this experiment are transition metal dichalcogenides, or TMDCs – an emerging class of semiconducting materials that consist of layers just a few atoms thick. There’s been an explosion of interest in TMDCs over the past few years as scientists explore their fundamental properties and potential uses in nanoelectronics and photonics.

    When two types of TMDC are stacked in alternating layers, electrons can flow from one layer to the next in a controllable way that people would like to harness for various applications.

    But until now, researchers who wanted to observe and study that flow had only been able to do it indirectly, by probing the material before and after the electrons had moved. The distances involved were just too short, and the electron speeds too fast, for today’s instruments to catch the flow of charge directly.

    At least that’s what they thought.

    Maxwell leads the way

    According to a famous set of equations named after physicist James Clerk Maxwell, pulses of current give off electromagnetic waves, which can vary from radio waves and microwaves to visible light and X-rays. In this case, the team realized that an electron’s journey from one TMDC layer to another should generate blips of terahertz waves – which fall between microwaves and infrared light on the electromagnetic spectrum – and that those blips could be detected with today’s state-of-the-art tools.

    “People had probably thought of this before, but dismissed the idea because they thought there was no way you could measure the current from electrons traveling such a small distance in such a small amount of material,” Ma said. “But if you do a back-of-the-envelope calculation, you see that if a current is really that fast you should be able to measure the emitted light, so we just tried.”

    Nudges from a laser

    The researchers, all investigators with the Stanford Institute for Materials and Energy Sciences (SIMES) at SLAC, tested their idea on a TMDC material made of molybdenum disulfide and tungsten disulfide.

    Working with SLAC/Stanford Professor Aaron Lindenberg, Ma and fellow postdoc Burak Guzelturk hit the material with ultrashort pulses of optical laser light to get the electrons moving and recorded the terahertz waves they gave off with a technique called time-domain terahertz emission spectroscopy. Those measurements not only revealed how far and fast the electric current traveled between layers, Ma said, but also the direction it traveled in. When the same two materials were stacked in reverse order, the current flowed in exactly the same way but in the opposite direction.

    “With the demonstration of this new technique, many exciting problems can now be addressed,” said Heinz, who led the team’s investigation. “For example, rotating one of the two crystal layers with respect to the other is known to dramatically change the electronic and optical properties of the combined layers. This method will allow us to directly follow the rapid motion of electrons from one layer to the other and see how this motion is affected by the relative positioning of the atoms.”

    Major funding for this work came from the DOE Office of Science and the Gordon and Betty Moore Foundation. The samples of material the team studied were grown at North Carolina State University.

    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 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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