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  • richardmitnick 8:26 am on May 15, 2015 Permalink | Reply
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    From BNL: “Intense Lasers Cook Up Complex, Self-Assembled Nanomaterials” 

    Brookhaven Lab

    May 13, 2015
    Justin Eure

    New technique developed at Brookhaven Lab makes self-assembly 1,000 times faster and could be used for industrial-scale solar panels and electronics

    1
    Brookhaven Lab scientist Kevin Yager (left) and postdoctoral researcher Pawel Majewski with the new Laser Zone Annealing instrument at the Center for Functional Nanomaterials.

    Nanoscale materials feature extraordinary, billionth-of-a-meter qualities that transform everything from energy generation to data storage. But while a nanostructured solar cell may be fantastically efficient, that precision is notoriously difficult to achieve on industrial scales. The solution may be self-assembly, or training molecules to stitch themselves together into high-performing configurations.

    Now, scientists at the U.S. Department of Energy’s Brookhaven National Laboratory have developed a laser-based technique to execute nanoscale self-assembly with unprecedented ease and efficiency.

    “We design materials that build themselves,” said Kevin Yager, a scientist at Brookhaven’s Center for Functional Nanomaterials (CFN). “Under the right conditions, molecules will naturally snap into a perfect configuration. The challenge is giving these nanomaterials the kick they need: the hotter they are, the faster they move around and settle into the desired formation. We used lasers to crank up the heat.”

    Yager and Brookhaven Lab postdoctoral researcher Pawel Majewski built a one-of-a-kind machine that sweeps a focused laser-line across a sample to generate intense and instantaneous spikes in temperature. This new technique, called Laser Zone Annealing (LZA), drives self-assembly at rates more than 1,000 times faster than traditional industrial ovens. The results are described in the journal ACS Nano.

    “We created extremely uniform self-assembled structures in less than a second,” Majewski said. “Beyond the extraordinary speed, our laser also reduced the defects and degradations present in oven-heated materials. That combination makes LZA perfect for carrying small-scale laboratory breakthroughs into industry.”

    The scientists prepared the materials and built the LZA instrument at the CFN. They then analyzed samples using advanced electron microscopy at CFN and x-ray scattering at Brookhaven’s now-retired National Synchrotron Light Source (NSLS)—both DOE Office of Science User Facilities.

    “It was enormously gratifying to see that our predictions were accurate—the enormous thermal gradients led to a correspondingly enormous acceleration!” Yager said.

    2
    Illustration of the Lazer Zone Annealing instrument showing the precise laser (green) striking the un-assembled polymer (purple). The extreme thermal gradients produced by the laser sweeping across the sample cause rapid and pristine self-assembly.

    Ovens versus lasers

    Imagine preparing a complex cake, but instead of baking it in the oven, a barrage of lasers heats it to perfection in an instant. Beyond that, the right cooking conditions will make the ingredients mix themselves into a picture-perfect dish. This nanoscale recipe achieves something equally extraordinary and much more impactful.

    The researchers focused on so-called block copolymers, molecules containing two linked blocks with different chemical structures and properties. These blocks tend to repel each other, which can drive the spontaneous formation of complex and rigid nanoscale structures.

    “The price of their excellent mechanical properties is the slow kinetics of their self-assembly,” Majewski said. “They need energy and time to explore possibilities until they find the right configuration.”

    In traditional block copolymer self-assembly, materials are heated in a vacuum-sealed oven. The sample is typically “baked” for a period of 24 hours or longer to provide enough kinetic energy for the molecules to snap into place—much too long for commercial viability. The long exposure to high heat also causes inevitable thermal degradation, leaving cracks and imperfections throughout the sample.

    The LZA process, however, offers sharp spikes of heat to rapidly excite the polymers without the sustained energy that damages the material.

    “Within milliseconds, the entire sample is beautifully aligned,” Yager said. “As the laser sweeps across the material, the localized thermal spikes actually remove defects in the nanostructured film. LZA isn’t just faster, it produces superior results.”

    LZA generates temperatures greater than 500 degrees Celsius, but the thermal gradients—temperature variations tied to direction and location in a material—can reach more than 4,000 degrees per millimeter. While scientists know that higher temperatures can accelerate self-assembly, this is the first proof of dramatic enhancement by extreme gradients.

    Built from scratch

    “Years ago, we observed a subtle hint that thermal gradients could improve self-assembly,” Yager said. “I became obsessed with the idea of creating more and more extreme gradients, which ultimately led to building this laser setup, and pioneering a new technique.”

    The researchers needed a high concentration of technical expertise and world-class facilities to move the LZA from proposal to execution.

    “Only at the CFN could we develop this technique so quickly,” Majewski said. “We could do rapid instrument prototyping and sample preparation with the on-site clean room, machine shop, and polymer processing lab. We then combined CFN electron microscopy with x-ray studies at NSLS for an unbeatable evaluation of the LZA in action.”

    Added Yager, “The ability to make new samples at the CFN and then walk across the street to characterize them in seconds at NSLS was key to this discovery. The synergy between these two facilities is what allowed us to rapidly iterate to an optimized design.”

    The scientists also developed a new microscale surface thermometry technique called melt-mark analysis to track the exact heat generated by the laser pulses and tune the instrument accordingly.

    “We burned a few films initially before we learned the right operating conditions,” Majewski said. “It was really exciting to see the first samples being rastered by the laser and then using NSLS to discover exactly what happened.”

    Future of the technique

    The LZA is the first machine of its kind in the world, but it signals a dramatic step forward in scaling up meticulously designed nanotechnology. The laser can even be used to “draw” structures across the surface, meaning the nanostructures can assemble in well-defined patterns. This unparalleled synthesis control opens the door to complex applications, including electronics.

    “There’s really no limit to the size of a sample this technique could handle,” Yager said. “In fact, you could run it in a roll-to-roll mode—one of the leading manufacturing technologies.”

    The scientists plan to further develop the new technique to create multi-layer structures that could have immediate impacts on anti-reflective coatings, improved solar cells, and advanced electronics.

    This research and operations at CFN and NSLS were funded by the DOE Office of Science.

    See the full article here.

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    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 7:56 am on May 14, 2015 Permalink | Reply
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    From MIT: “Researchers build new fermion microscope” 


    MIT News

    May 13, 2015
    Jennifer Chu

    1
    Graduate student Lawrence Cheuk adjusts the optics setup for laser cooling of sodium atoms. Photo: Jose-Luis Olivares/MIT

    2
    Laser beams are precisely aligned before being sent into the vacuum chamber. Photo: Jose-Luis Olivares/MIT

    3
    Sodium atoms diffuse out of an oven to form an atomic beam, which is then slowed and trapped using laser light. Photo: Jose-Luis Olivares/MIT

    4
    A Quantum gas microscope for fermionic atoms. The atoms, potassium-40, are cooled during imaging by laser light, allowing thousands of photons to be collected by the microscope. Credit: Lawrence Cheuk/MIT

    5
    The Fermi gas microscope group: (from left) graduate students Katherine Lawrence and Melih Okan, postdoc Thomas Lompe, graduate student Matt Nichols, Professor Martin Zwierlein, and graduate student Lawrence Cheuk. Photo: Jose-Luis Olivares/MIT

    Instrument freezes and images 1,000 individual fermionic atoms at once.

    Fermions are the building blocks of matter, interacting in a multitude of permutations to give rise to the elements of the periodic table. Without fermions, the physical world would not exist.

    Examples of fermions are electrons, protons, neutrons, quarks, and atoms consisting of an odd number of these elementary particles. Because of their fermionic nature, electrons and nuclear matter are difficult to understand theoretically, so researchers are trying to use ultracold gases of fermionic atoms as stand-ins for other fermions.

    But atoms are extremely sensitive to light: When a single photon hits an atom, it can knock the particle out of place — an effect that has made imaging individual fermionic atoms devilishly hard.

    Now a team of MIT physicists has built a microscope that is able to see up to 1,000 individual fermionic atoms. The researchers devised a laser-based technique to trap and freeze fermions in place, and image the particles simultaneously.

    The new imaging technique uses two laser beams trained on a cloud of fermionic atoms in an optical lattice. The two beams, each of a different wavelength, cool the cloud, causing individual fermions to drop down an energy level, eventually bringing them to their lowest energy states — cool and stable enough to stay in place. At the same time, each fermion releases light, which is captured by the microscope and used to image the fermion’s exact position in the lattice — to an accuracy better than the wavelength of light.

    With the new technique, the researchers are able to cool and image over 95 percent of the fermionic atoms making up a cloud of potassium gas. Martin Zwierlein, a professor of physics at MIT, says an intriguing result from the technique appears to be that it can keep fermions cold even after imaging.

    “That means I know where they are, and I can maybe move them around with a little tweezer to any location, and arrange them in any pattern I’d like,” Zwierlein says.

    Zwierlein and his colleagues, including first author and graduate student Lawrence Cheuk, have published their results today in the journal Physical Review Letters.

    Seeing fermions from bosons

    For the past two decades, experimental physicists have studied ultracold atomic gases of the two classes of particles: fermions and bosons — particles such as photons that, unlike fermions, can occupy the same quantum state in limitless numbers. In 2009, physicist Marcus Greiner at Harvard University devised a microscope that successfully imaged individual bosons in a tightly spaced optical lattice. This milestone was followed, in 2010, by a second boson microscope, developed by Immanuel Bloch’s group at the Max Planck Institute of Quantum Optics.

    These microscopes revealed, in unprecedented detail, the behavior of bosons under strong interactions. However, no one had yet developed a comparable microscope for fermionic atoms.

    “We wanted to do what these groups had done for bosons, but for fermions,” Zwierlein says. “And it turned out it was much harder for fermions, because the atoms we use are not so easily cooled. So we had to find a new way to cool them while looking at them.”

    Techniques to cool atoms ever closer to absolute zero have been devised in recent decades. Carl Wieman, Eric Cornell, and MIT’s Wolfgang Ketterle were able to achieve Bose-Einstein condensation in 1995, a milestone for which they were awarded the 2001 Nobel Prize in physics. Other techniques include a process using lasers to cool atoms from 300 degrees Celsius to a few ten-thousandths of a degree above absolute zero.

    A clever cooling technique

    And yet, to see individual fermionic atoms, the particles need to be cooled further still. To do this, Zwierlein’s group created an optical lattice using laser beams, forming a structure resembling an egg carton, each well of which could potentially trap a single fermion. Through various stages of laser cooling, magnetic trapping, and further evaporative cooling of the gas, the atoms were prepared at temperatures just above absolute zero — cold enough for individual fermions to settle onto the underlying optical lattice. The team placed the lattice a mere 7 microns from an imaging lens, through which they hoped to see individual fermions.

    However, seeing fermions requires shining light on them, causing a photon to essentially knock a fermionic atom out of its well, and potentially out of the system entirely.

    “We needed a clever technique to keep the atoms cool while looking at them,” Zwierlein says.

    His team decided to use a two-laser approach to further cool the atoms; the technique manipulates an atom’s particular energy level, or vibrational energy. Each atom occupies a certain energy state — the higher that state, the more active the particle is. The team shone two laser beams of differing frequencies at the lattice. The difference in frequencies corresponded to the energy between a fermion’s energy levels. As a result, when both beams were directed at a fermion, the particle would absorb the smaller frequency, and emit a photon from the larger-frequency beam, in turn dropping one energy level to a cooler, more inert state. The lens above the lattice collects the emitted photon, recording its precise position, and that of the fermion.

    Zwierlein says such high-resolution imaging of more than 1,000 fermionic atoms simultaneously would enhance our understanding of the behavior of other fermions in nature — particularly the behavior of electrons. This knowledge may one day advance our understanding of high-temperature superconductors, which enable lossless energy transport, as well as quantum systems such as solid-state systems or nuclear matter.

    “The Fermi gas microscope, together with the ability to position atoms at will, might be an important step toward the realization of a quantum computer based on fermions,” Zwierlein says. “One would thus harness the power of the very same intricate quantum rules that so far hamper our understanding of electronic systems.”

    Zwierlein says it is a good time for Fermi gas microscopists: Around the same time his group first reported its results, teams from Harvard and the University of Strathclyde in Glasgow also reported imaging individual fermionic atoms in optical lattices, indicating a promising future for such microscopes.

    Zoran Hadzibabic, a professor of physics at Trinity College, says the group’s microscope is able to detect individual atoms “with almost perfect fidelity.”

    “They detect them reliably, and do so without affecting their positions — that’s all you want,” says Hadzibabic, who did not contribute to the research. “So far they demonstrated the technique, but we know from the experience with bosons that that’s the hardest step, and I expect the scientific results to start pouring out.”

    This research was funded in part by the National Science Foundation, the Air Force Office of Scientific Research, the Office of Naval Research, the Army Research Office, and the David and Lucile Packard Foundation.

    See the full article here.

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  • richardmitnick 12:41 pm on April 6, 2015 Permalink | Reply
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    From LLNL: “Lawrence Livermore deploys world’s highest peak-power laser diode arrays” 


    Lawrence Livermore National Laboratory

    Mar. 12, 2015

    Breanna Bishop
    bishop33@llnl.gov
    925-423-9802

    1
    To drive the diode arrays, LLNL needed to develop a completely new type of pulsed-power system, which supplies the arrays with electrical power by drawing energy from the grid and converting it to extremely high-current, precisely-shaped electrical pulses.Photos by Damien Jemison.

    Lawrence Livermore National Laboratory (LLNL) has installed and commissioned the highest peak power laser diode arrays in the world, representing total peak power of 3.2 megawatts (MW).

    The diode arrays are a key component of the High-Repetition-Rate Advanced Petawatt Laser System (HAPLS), which is currently under construction at LLNL. When completed, the HAPLS laser system will be installed in the European Union’s Extreme Light Infrastructure (ELI) Beamlines facility, under construction in the Czech Republic.

    HAPLS is designed to be capable of generating peak powers greater than one petawatt (1 quadrillion watts, or 1015) at a repetition rate of 10 Hertz, with each pulse lasting 30 femtoseconds (30 quadrillionths of a second). This very high repetition rate will be a major advancement over current petawatt system technologies, which rely on flashlamps as the primary pump source and can fire a maximum of once per second. In HAPLS, the diode arrays fire 10 times per second, delivering kilojoule laser pulses to the final power amplifier. The HAPLS is being built and commissioned at LLNL and then installed and integrated into the ELI Beamlines facility starting in 2017.

    “The Extreme Light Infrastructure in Europe is building international scientific user facilities equipped with cutting-edge laser technology to explore fundamental science and applications,” said HAPLS Program Director Constantin Haefner. “Livermore is one of the world leaders in high-energy, high-average-power laser systems, and ELI Beamlines in Prague has partnered with us to build HAPLS, a new-generation petawatt laser system, enabling new avenues of scientific research.”

    To meet the rigorous design specification for HAPLS, LLNL had to look past current laser pump technology. Previously, high energy, scientific laser systems – such as LLNL’s National Ignition Facility [NIF] – utilized flashlamp technology.

    Livermore NIF
    NIF

    Intense flashes of white light from these giant flashlamps “pump” the laser-active atoms in large slabs of laser glass to a higher or more “excited” energy state. In order to get to the high repetition rate required by HAPLS, the team needed to come up with technologies that transfers less heat than flashlamps and removes it at faster rates, which lessens the time between laser shots.

    2
    The diode arrays represent total peak power of 3.2 megawatts, making them the highest peak power diode arrays in the world. They are a key component of the High-Repetition-Rate Advanced Petawatt Laser System (HAPLS), which will be the world’s highest repetition rate petawatt laser system when completed.

    “Flashlamp technology for lasers has been around for more than 50 years, and we’ve pretty much pushed the limits of that technology and maxed out what we can do with them,” said Andy Bayramian, systems architect on HAPLS. “We’ve closed the books on flashlamps and started a new one with these laser diode arrays, enabling a far more advanced class of high-energy laser systems.”

    To develop these diode arrays, LLNL partnered with Lasertel Inc., a member of the Finmeccanica Group and a developer of high-powered semiconductor laser pump modules. Lasertel combined advanced semiconductor laser technology with novel micro-optics to supply the megawatt-class pump modules in a reliable, integrated platform.

    “We are thrilled to be working with LLNL, who continues to push the boundaries for high-energy laser systems. Our collaboration has enabled several new benchmarks for laser performance to be set in a remarkably short period of time,” Lasertel President Mark McElhinney said. “This is a validation of the significant progress that has been made toward the routine production of high-energy lasers for revolutionary commercial applications and groundbreaking scientific research.”

    In addition, LLNL needed to develop a completely new type of pulsed-power system in order to drive the diode arrays. The pulsed-power system supplies the arrays with electrical power by drawing energy from the grid and converting it to extremely high-current, precisely shaped electrical pulses. Each power supply is capable of driving 40,000 amps. Livermore holds a patent on this technology.

    High-average-power, high-energy laser systems enabled by these technologies will drive international scientific research in areas as diverse as advanced imaging, particle acceleration, biophysics, chemistry and quantum physics in addition to national security applications and industrial processes such as laser peening and laser fusion.

    “Combining Lasertel’s diode technology with Livermore’s highly compact and efficient pulsed-power system is THE enabling technology to drive high energy lasers at rep rate,” Haefner said. “This combination of expertise has created a robust, stable, laser driver platform with high reliability, cost efficiency and – most important for the scientific user community – long-term scalability to maintain competitiveness in the future.”

    See the full article here.

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    Operated by Lawrence Livermore National Security, LLC, for the Department of Energy’s National Nuclear Security
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  • richardmitnick 2:46 pm on February 20, 2015 Permalink | Reply
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    From Nature: “Saudi Arabia opens top-notch laser lab” 

    Nature Mag
    Nature

    17 February 2015
    Alison Abbott

    1
    Rector of King Saud University, Badran Al-Omar (left), and Abdallah Azzeer attend the opening ceremony for the Attosecond Science Laboratory.

    A cutting-edge laser facility — the first of its kind in the Arab world — opened this week at Saudi Arabia’s oldest and largest university. The launch pushes forward the country’s ambitions to become a leader in science and builds on a collaboration with Western scientists that has required some cultural adjustments.

    The Attosecond Science Laboratory at King Saud University (KSU) in Riyadh hosts an ‘attosecond laser’, which generates ultrashort pulses of light, lasting just a few billionths of a billionth of a second, that can image otherwise invisible electrons as they move similarly fast within atoms. Attosecond lasers were invented in 2001, and facilities now exist at dozens of sites around the world. The Saudi Arabian facility is the result of a collaboration that began in 2008 with the Max Planck Institute of Quantum Optics (MPQ) in Garching, Germany, which hosts its own attosecond laser, and the Ludwig Maximilian University of Munich.

    “It is very exciting that the frontier of attosecond science is now having its outpost in the Gulf state,” says Olga Smirnova, an atomic physicist at the Max Born Institute in Berlin.

    Saudi Arabia is known for its oil wealth, and in 2002 its government decided that science was the key to incubating a more diverse economy. Its strategy comprises heavy financial investment and forging partnerships with leading research institutions abroad — and it seems to be working. In the past five years, the number of scientific papers produced by researchers in Saudi Arabia has skyrocketed. The quality of the research has now overtaken that of Turkey and Iran, according to impact metrics known as SNIP (Source Normalized Impact per Paper) from the University of Leiden in the Netherlands. Prince Turki Bin Saud Bin Mohammad Al Saud, who heads Saudi Arabia’s National Science, Technology and Innovation Plan, told Nature’s News team that science funding has been doubled from this year and that the country is on track to reach Western levels by the mid-2020s.

    Attosecond lasers quickly became fundamental tools in atomic physics after the first atto­second laser pulses were reported in 2001 by a team led by the MPQ’s Ferenc Krausz, who heads the Attosecond Science Lab (M. Hentschel et al. Nature 414, 509–513; 2001).

    The lasers have since moved into the realm of molecular sciences, including condensed-matter systems and molecular biology, where they are being used to investigate how the movement of electrons can initiate changes in the structure of molecules. “They provide an exquisitely sharp temporal scalpel for dissecting the inner workings of matter,” says laser physicist John Tisch of Imperial College London.

    One of the first planned experiments for the KSU laser will study the behaviour of electrons in atoms of melanin, best known as the pigment that protects skin from the sun’s ultra­violet rays. No one knows why ultraviolet photons do not normally break the chemical bonds in the molecule when they hit it, but it is assumed that melanin’s electrons redistribute — and diffuse — the energy among themselves. The experiment at KSU will test this hypothesis by developing extremely short, high-intensity ultraviolet pulses to excite the electrons, and will then capture their movements with the attosecond laser.

    2
    Abdallah Azzeer (left) and Ferenc Krausz head up a collaboration at King Saud University in Riyadh.

    The collaboration with Saudi Arabia gives Krausz the chance to enter totally new territory. He will work with oncologist Jean-Marc Nabholtz — who moved to KSU last year to head its National Comprehensive Cancer Center — to adapt the laser to generate pulses of infrared light for analysing proteins and nucleic acids in blood samples from people with cancer. The aim will be to find molecular ‘fingerprints’ that might diagnose cancers, or predict response to therapy or the future onset of a cancer.

    The value of such a source of infrared light, Krausz says, is that a table-top-size laser system could be developed and used at patients’ bedsides. Currently, the only sources of such radiation are synchrotrons, which require large, expensive infrastructures. Because Krausz has little experience in this area, it would have been hard for him to obtain funding in Germany for such medical applications, he says.

    The place of women in Saudi society and education, and the country’s human-rights record, have presented challenges for members of the collaboration. At KSU, which was founded in 1957, male and female students have separate campuses. No rule forbids women from entering the new lab, says Abdallah Azzeer, who leads the KSU side of the laser collaboration, but mixing of the sexes contravenes cultural norms. “We will make special arrangements to ensure their access,” he says. One possibility, he adds, might be to train female PhD students in handling the equipment so that they can supervise female undergraduates whose parents do not want them to attend mixed classes.

    Krausz has had to get used to working in a segregated environment during his time at KSU. All the lectures are given in the men’s campus and beamed over to the women’s campus, and Krausz remembers being extremely startled the first time he received a disembodied question from a female student over loudspeakers.

    He thought long and hard about working with Saudi Arabia, he says. As a Hungarian who left for the West in 1987 at the age of 25, he is hypersensitive to human-rights issues. But not long before he decided to collaborate with KSU in 2008, he had cancelled a trip to China in protest against a clamp-down on press freedom there, and then regretted the decision. It achieved nothing save the embarrassment of the scientists, he says, and he concluded that, in such cases, “the best thing is to talk to each other and learn each other’s problems”.

    He found himself genuinely moved by the enthusiasm for science he encountered on his first visit to KSU later that year. “It felt like a small revolution was happening,” he says. “I thought about how I would have felt in the same situation in Hungary — I might have stayed.”

    See the full article here.

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  • richardmitnick 9:54 am on January 21, 2015 Permalink | Reply
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    From U Rochester: “Laser-generated surface structures create extremely water-repellent metals” 

    U Rochester bloc

    University of Rochester

    January 20, 2015
    Leonor Sierra

    1
    Professor Chunlei Guo has developed a technique that uses lasers to render materials hydrophobic, illustrated in this image of a water droplet bouncing off a treated sample. Photo by J. Adam Fenster / University of Rochester.

    Super-hydrophobic properties could lead to applications in solar panels, sanitation and as rust-free metals

    Scientists at the University of Rochester have used lasers to transform metals into extremely water repellent, or super-hydrophobic, materials without the need for temporary coatings.

    Super-hydrophobic materials are desirable for a number of applications such as rust prevention, anti-icing, or even in sanitation uses. However, as Rochester’s Chunlei Guo explains, most current hydrophobic materials rely on chemical coatings.

    In a paper published today in the Journal of Applied Physics, Guo and his colleague at the University’s Institute of Optics, Anatoliy Vorobyev, describe a powerful and precise laser-patterning technique that creates an intricate pattern of micro- and nanoscale structures to give the metals their new properties. This work builds on earlier research by the team in which they used a similar laser-patterning technique that turned metals black. Guo states that using this technique they can create multifunctional surfaces that are not only super-hydrophobic but also highly-absorbent optically.

    Guo adds that one of the big advantages of his team’s process is that “the structures created by our laser on the metals are intrinsically part of the material surface.” That means they won’t rub off. And it is these patterns that make the metals repel water.

    “The material is so strongly water-repellent, the water actually gets bounced off. Then it lands on the surface again, gets bounced off again, and then it will just roll off from the surface,” said Guo, professor of optics at the University of Rochester. That whole process takes less than a second.

    The materials Guo has created are much more slippery than Teflon—a common hydrophobic material that often coats nonstick frying pans. Unlike Guo’s laser-treated metals, the Teflon kitchen tools are not super-hydrophobic. The difference is that to make water to roll-off a Teflon coated material, you need to tilt the surface to nearly a 70-degree angle before the water begins to slide off. You can make water roll off Guo’s metals by tilting them less than five degrees.

    As the water bounces off the super-hydrophobic surfaces, it also collects dust particles and takes them along for the ride. To test this self-cleaning property, Guo and his team took ordinary dust from a vacuum cleaner and dumped it onto the treated surface. Roughly half of the dust particles were removed with just three drops of water. It took only a dozen drops to leave the surface spotless. Better yet, it remains completely dry.

    Guo is excited by potential applications of super-hydrophobic materials in developing countries. It is this potential that has piqued the interest of the Bill and Melinda Gates Foundation, which has supported the work.

    “In these regions, collecting rain water is vital and using super-hydrophobic materials could increase the efficiency without the need to use large funnels with high-pitched angles to prevent water from sticking to the surface,” says Guo. “A second application could be creating latrines that are cleaner and healthier to use.”

    Latrines are a challenge to keep clean in places with little water. By incorporating super-hydrophobic materials, a latrine could remain clean without the need for water flushing.

    2
    3
    Professor Chunlei Guo has developed a technique that uses lasers to render materials hydrophobic, illustrated in these images of water droplets bouncing off a treated sample. // Photos by J. Adam Fenster / University of Rochester

    But challenges still remain to be addressed before these applications can become a reality, Guo states. It currently takes an hour to pattern a 1 inch by 1 inch metal sample, and scaling up this process would be necessary before it can be deployed in developing countries. The researchers are also looking into ways of applying the technique to other, non-metal materials.

    Guo and Vorobyev use extremely powerful, but ultra-short, laser pulses to change the surface of the metals. A femtosecond laser pulse lasts on the order of a quadrillionth of a second but reaches a peak power equivalent to that of the entire power grid of North America during its short burst.

    Guo is keen to stress that this same technique can give rise to multifunctional metals. Metals are naturally excellent reflectors of light. That’s why they appear to have a shiny luster. Turning them black can therefore make them very efficient at absorbing light. The combination of light-absorbing properties with making metals water repellent could lead to more efficient solar absorbers – solar absorbers that don’t rust and do not need much cleaning.

    Guo’s team had previously blasted materials with the lasers and turned them hydrophilic, meaning they attract water. In fact, the materials were so hydrophilic that putting them in contact with a drop of water made water run “uphill.”

    Guo’s team is now planning on focusing on increasing the speed of patterning the surfaces with the laser, as well as studying how to expand this technique to other materials such as semiconductors or dielectrics, opening up the possibility of water repellent electronics.

    Funding was provided by the Bill & Melinda Gates Foundation and the United States Air Force Office of Scientific Research.

    The article, Multifunctional surfaces produced by femtosecond laser pulses, was published in the Journal of Applied Physics on January 20, 2015 (DOI: 10.1063/1.4905616). It can be accessed at: http://scitation.aip.org/content/aip/journal/jap/117/3/10.1063/1.4905616

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    The University of Rochester is one of the country’s top-tier research universities. Our 158 buildings house more than 200 academic majors, more than 2,000 faculty and instructional staff, and some 10,500 students—approximately half of whom are women.

    Learning at the University of Rochester is also on a very personal scale. Rochester remains one of the smallest and most collegiate among top research universities, with smaller classes, a low 10:1 student to teacher ratio, and increased interactions with faculty.

     
  • richardmitnick 3:28 pm on December 9, 2014 Permalink | Reply
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    From livescience: “Laser-Zapping Experiment Simulates Beginnings of Life on Earth” 

    Livescience

    December 08, 2014
    Tanya Lewis

    The origin of life on Earth about 4 billion years ago remains one of the biggest unsolved mysteries of science, but a new study is shedding light on the matter.

    To recreate the conditions thought to exist on Earth when life began, scientists used a giant laser to ignite chemical reactions that converted a substance found on the early Earth into the molecular building blocks of DNA, the blueprint for life.

    l
    The Asterix laser delivers about 1,000 Joules of power at its peak, which is equivalent to the amount produced by an atomic power station.
    Credit: Dagmar Civisova

    The findings not only offer support for theories of how life first formed, but could also aid in the search for signs of life elsewhere in the universe, the researchers said.

    The beginning of life coincides with a hypothetical event that occurred 4 billion to 3.85 billion years ago, known as the Late Heavy Bombardment, in which asteroids pummeled Earth and the solar system’s other inner planets. These impacts may have provided the energy to jumpstart the chemistry of life, scientists say.

    In 1952, the chemists Stanley Miller and Harold Urey conducted a famous experiment at the University of Chicago in which they simulated the conditions thought to be present on early Earth. This experiment was intended to show how the basic materials for life could be produced from nonliving matter.

    Recent studies suggest that asteroid impacts may break down formamide — a molecule thought to be present in early Earth’s atmosphere — into genetic building blocks of DNA and its cousin RNA, called nucleobases.

    In their new study, chemist Svatopluk Civiš, of the Academy of Sciences of the Czech Republic, and his colleagues used a high-powered laser to break down ionized formamide gas, or plasma, to mimic an asteroid strike on early Earth.

    “We want[ed] to simulate the impact of some extraterrestrial body [during] an early stage of the atmosphere of Earth,” Civiš told Live Science.

    They used the Asterix iodine laser, a 490-feet-long (150 meters) machine that packs about 1,000 Joules of power at its peak, which is equivalent to the amount produced by an atomic power station, Civiš said. The laser was only switched on for half a nanosecond, however, because that is comparable to the time frame for an asteroid impact, he said.

    The reaction produced scalding temperatures of up to 7,640 degrees Fahrenheit (4,230 degrees Celsius), sending out a shock wave and spewing intense ultraviolet and X-ray radiation. The chemical fireworks produced four of the nucleobases that collectively make up DNA and RNA: adenine, guanine, cytosine and uracil.

    Using sensitive spectroscopic instruments, the researchers observed the intermediate products of the chemical reactions. These instruments measure the chemical fingerprint of the molecules formed during the course of a reaction. Afterward, the team used a mass spectrometer, a device that measures the masses of chemicals, to detect the final products of the reactions.

    The breakdown of formamide produced two highly reactive chemicals or “free radicals” of Carbon and Nitrogen (CN) and Nitrogen and Hydrogen (NH), which could have reacted with formamide itself to produce the genetic nucleobases, the researchers said.

    The findings, detailed today (Dec. 8) in the journal Proceedings of the National Academy of Sciences, provide a more detailed mechanism for how the basic chemistry of life got started.

    The results of the study could offer clues for how to look for molecules that could give rise to life on other planets, the researchers said. The Late Heavy Bombardment could have created similar reactions on other rocky planets in the solar system, but these may not have had water and other conditions necessary for life, Civiš said. For example, Earth contained clay, which may have protected these building blocks of life from the very bombardment that created them.

    “[T]he emergence of terrestrial life is not the result of an accident but a direct consequence of the conditions on the primordial Earth and its surroundings,” the scientists wrote in the study.

    Editor’s Note: This article was updated at Dec. 9, 2014 at 11:28 p.m. ET, to correct the number of nucleobases that were synthesized in the experiment. These did not include the nucleobase thymine.

    See the full article here.

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  • richardmitnick 4:54 pm on December 8, 2014 Permalink | Reply
    Tags: , , Laser Technology   

    From LBL: “World Record for Compact Particle Accelerator” 

    Berkeley Logo

    Berkeley Lab

    December 8, 2014
    Kate Greene 510-486-4404

    Using one of the most powerful lasers in the world, researchers have accelerated subatomic particles to the highest energies ever recorded from a compact accelerator.

    l
    A 9 cm-long capillary discharge waveguide used in BELLA experiments to generate multi-GeV electron beams. The plasma plume has been made more prominent with the use of HDR photography. Credit: Roy Kaltschmidt

    The team, from the U.S. Department of Energy’s Lawrence Berkeley National Lab (Berkeley Lab), used a specialized petawatt laser and a charged-particle gas called plasma to get the particles up to speed. The setup is known as a laser-plasma accelerator, an emerging class of particle accelerators that physicists believe can shrink traditional, miles-long accelerators to machines that can fit on a table.

    The researchers sped up the particles—electrons in this case—inside a nine-centimeter long tube of plasma. The speed corresponded to an energy of 4.25 giga-electron volts. The acceleration over such a short distance corresponds to an energy gradient 1000 times greater than traditional particle accelerators and marks a world record energy for laser-plasma accelerators.

    “This result requires exquisite control over the laser and the plasma,” says Dr. Wim Leemans, director of the Accelerator Technology and Applied Physics Division at Berkeley Lab and lead author on the paper. The results appear in the most recent issue of Physical Review Letters.

    Traditional particle accelerators, like the Large Hadron Collider at CERN, which is 17 miles in circumference, speed up particles by modulating electric fields inside a metal cavity. It’s a technique that has a limit of about 100 mega-electron volts per meter before the metal breaks down.

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC atCERN

    Laser-plasma accelerators take a completely different approach. In the case of this experiment, a pulse of laser light is injected into a short and thin straw-like tube that contains plasma. The laser creates a channel through the plasma as well as waves that trap free electrons and accelerate them to high energies. It’s similar to the way that a surfer gains speed when skimming down the face of a wave.

    The record-breaking energies were achieved with the help of BELLA (Berkeley Lab Laser Accelerator), one of the most powerful lasers in the world. BELLA, which produces a quadrillion watts of power (a petawatt), began operation just last year.

    LBL BellaBELLA at LBL

    “It is an extraordinary achievement for Dr. Leemans and his team to produce this record-breaking result in their first operational campaign with BELLA,” says Dr. James Symons, associate laboratory director for Physical Sciences at Berkeley Lab.

    In addition to packing a high-powered punch, BELLA is renowned for its precision and control. “We’re forcing this laser beam into a 500 micron hole about 14 meters away, “ Leemans says. “The BELLA laser beam has sufficiently high pointing stability to allow us to use it.” Moreover, Leemans says, the laser pulse, which fires once a second, is stable to within a fraction of a percent. “With a lot of lasers, this never could have happened,” he adds.

    cs
    Computer simulation of the plasma wakefield as it evolves over the length of the 9-cm long channel. Credit: Berkeley Lab

    At such high energies, the researchers needed to see how various parameters would affect the outcome. So they used computer simulations at the National Energy Research Scientific Computing Center (NERSC) to test the setup before ever turning on a laser. “Small changes in the setup give you big perturbations,” says Eric Esarey, senior science advisor for the Accelerator Technology and Applied Physics Division at Berkeley Lab, who leads the theory effort. “We’re homing in on the regions of operation and the best ways to control the accelerator.”

    In order to accelerate electrons to even higher energies—Leemans’ near-term goal is 10 giga-electron volts—the researchers will need to more precisely control the density of the plasma channel through which the laser light flows. In essence, the researchers need to create a tunnel for the light pulse that’s just the right shape to handle more-energetic electrons. Leemans says future work will demonstrate a new technique for plasma-channel shaping.

    Multi-GeV electron beams from capillary-discharge-guided subpetawatt laser pulses in the self-trapping regime by W. P. Leemans, A. J. Gonsalves, H.-S. Mao, et al. was published in Physical Review Letters on December 8, 2014.

    See the full article here.

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  • richardmitnick 2:58 pm on October 30, 2014 Permalink | Reply
    Tags: , Laser Technology, ,   

    From LBL: “Lord of the Microrings” 

    Berkeley Logo

    Berkeley Lab

    October 30, 2014
    Lynn Yarris (510) 486-5375

    A significant breakthrough in laser technology has been reported by the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley. Scientists led by Xiang Zhang, a physicist with joint appointments at Berkeley Lab and UC Berkeley, have developed a unique microring laser cavity that can produce single-mode lasing even from a conventional multi-mode laser cavity. This ability to provide single-mode lasing on demand holds ramifications for a wide range of applications including optical metrology and interferometry, optical data storage, high-resolution spectroscopy and optical communications.

    “Losses are typically undesirable in optics but, by deliberately exploiting the interplay between optical loss and gain based on the concept of parity-time symmetry, we have designed a microring laser cavity that exhibits intrinsic single-mode lasing regardless of the gain spectral bandwidth,” says Zhang, who directs Berkeley Lab’s Materials Sciences Division and is UC Berkeley’s Ernest S. Kuh Endowed Chair Professor. “This approach also provides an experimental platform to study parity-time symmetry and phase transition phenomena that originated from quantum field theory yet have been inaccessible so far in experiments. It can fundamentally broaden optical science at both semi-classical and quantum levels”

    zz
    Xiang Zhang, director of Berkeley Lab’s Materials Sciences Division. (Photo by Roy Kaltschmidt)

    Zhang, who also directs the National Science Foundation’s Nano-scale Science and Engineering Center, and is a member of the Kavli Energy NanoSciences Institute at Berkeley, is the corresponding author of a paper in Science that describes this work. The paper is titled Single-Mode Laser by Parity-time Symmetry Breaking. Co-authors are Liang Feng, Zi Jing Wong, Ren-Min Ma and Yuan Wang.

    A laser cavity or resonator is the mirrored component of a laser in which light reflected multiple times yields a standing wave at certain resonance frequencies called modes. Laser cavities typically support multiple modes because their dimensions are much larger than optical wavelengths. Competition between modes limits the optical gain in amplitude and results in random fluctuations and instabilities in the emitted laser beams.

    “For many applications, single-mode lasing is desirable for its stable operation, better beam quality, and easier manipulation,” Zhang says. “Light emission from a single-mode laser is monochromatic with low phase and intensity noises, but creating sufficiently modulated optical gain and loss to obtain single-mode lasing has been a challenge.”
    Scanning electron microscope image of the fabricated PT symmetry microring laser cavity.

    image
    Scanning electron microscope image of the fabricated PT symmetry microring laser cavity.

    While mode manipulation and selection strategies have been developed to achieve single-mode lasing, each of these strategies has only been applicable to specific configurations. The microring laser cavity developed by Zhang’s group is the first successful concept for a general design. The key to their success is using the concept of the breaking of parity-time (PT) symmetry. The law of parity-time symmetry dictates that the properties of a system, like a beam of light, remain the same even if the system’s spatial configuration is reversed, like a mirror image, or the direction of time runs backward. Zhang and his group discovered a phenomenon called “thresholdless parity-time symmetry breaking” that provides them with unprecedented control over the resonant modes of their microring laser cavity, a critical requirement for emission control in laser physics and applications.

    lf
    Liang Feng

    “Thresholdless PT symmetry breaking means that our light beam undergoes symmetry breaking once the gain/loss contrast is introduced no matter how large this contrast is,” says Liang Feng, lead author of the Science paper, a recent posdoc in Zhang’s group and now an assistant professor with the University at Buffalo. “In other words, the threshold for PT symmetry breaking is zero gain/loss contrast.”

    Zhang, Feng and the other members of the team were able to exploit the phenomenon of thresholdless PT symmetry breaking through the fabrication of a unique microring laser cavity. This cavity consists of bilayered structures of chromium/germanium arranged periodically in the azimuthal direction on top of a microring resonator made from an indium-gallium-arsenide-phosphide compound on a substrate of indium phosphide. The diameter of the microring is 9 micrometers.

    “The introduced rotational symmetry in our microring resonator is continuous, mimicking an infinite system,” says Feng. “The counterintuitive discovery we made is that PT symmetry does not hold even at an infinitesimal gain/loss modulation when a system is rotationally symmetric. This was not observed in previous one-dimensional PT modulation systems because those finite systems did not support any continuous symmetry operations.”

    Using the continuous rotational symmetry of their microring laser cavity to facilitate thresholdless PT symmetry breaking,

    Zhang, Feng and their collaborators are able to delicately manipulate optical gain and loss in such a manner as to ultimately yield single-mode lasing.

    “PT symmetry breaking means an optical mode can be gain-dominant for lasing, whereas PT symmetry means all the modes remain passive,” says Zi-Jing Wong, co-lead author and a graduate student in Zhang’s group. “With our microring laser cavity, we facilitate a desired mode in PT symmetry breaking, while keeping all other modes PT symmetric. Although PT symmetry breaking by itself cannot guarantee single-mode lasing, when acting together with PT symmetry for all other modes, it facilitates single-mode lasing.”

    In their Science paper, the researchers suggest that single-mode lasing through PT-symmetry breaking could pave the way to next generation optoelectronic devices for communications and computing as it enables the independent manipulation of multiple laser beams without the “crosstalk” problems that plague today’s systems. Their microring laser cavity concept might also be used to engineer optical modes in a typical multi-mode laser cavity to create a desired lasing mode and emission pattern.

    “Our microring laser cavities could also replace the large laser boxes that are routinely used in labs and industry today,” Feng says. “Moreover, the demonstrated single-mode operation regardless of gain spectral bandwidth may create a laser chip carrying trillions of informational signals at different frequencies. This would make it possible to shrink a huge datacenter onto a tiny photonic chip.”

    This research was supported by the Office of Naval Research MURI program.

    See the full article here.

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  • richardmitnick 4:53 pm on October 8, 2014 Permalink | Reply
    Tags: , Laser Technology,   

    From LLNL: “LLNL to play key role in 10 petawatt laser project” 


    Lawrence Livermore National Laboratory

    10/08/2014
    Breanna Bishop, LLNL, (925) 423-9802, bishop33@llnl.gov

    Lawrence Livermore National Laboratory has once again been selected to support the development and construction of an ultra-intense laser system for the European Union’s Extreme Light Infrastructure Beamlines (ELI-Beamlines) in the Czech Republic.

    beam
    3D CAD rendering of the 10PW laser system. Credit: National Energetics Inc.

    A consortium led by National Energetics Inc., in partnership with Ekspla UAB, was awarded the contract to construct the system, which will be the most powerful laser of its class in the world, capable of producing peak power in excess of 10 petawatts (PW). Due to LLNL’s long-standing expertise in laser research and development, the consortium selected the Laboratory for a $3.5 million subcontract to support development of this system.

    “The award of this project is another clear statement of the internationally leading nature of LLNL’s laser design capability,” said Mike Dunne, LLNL’s director of laser fusion energy. “It also is another great example of where LLNL is helping move forward the global state-of-the-art of high power lasers, working collaboratively with the U.S. and European industry and academia. We are very excited to work with the National Energetics consortium, which has a very compelling approach to reaching the 10 petawatt goal.”

    Under the subcontract, LLNL will be responsible for: contributing to the physics design of the liquid-cooled laser amplifier, allowing it to get to the high energies required for accessing 10 PW power; contributing to the physics and engineering design of the short pulse compressor, which takes the high energy beam and compresses it to the required pulse length; and production of the large aperture diffraction gratings for this compressor.

    This system will be one of the four major beamlines at the new ELI-Beamlines facility. In addition to work on this beamline, LLNL also is responsible for the design, development and installation of a second beamline at the facility, through a more than $45 million contract awarded in 2013. When commissioned to its full design performance, the laser system, called the “High repetition-rate Advanced Petawatt Laser System” (HAPLS), will be the world’s highest average power PW laser system. The two systems will thus offer a highly attractive capability for the new ELI-Beamlines facility, which will appeal to academic and industrial researchers from across the world.

    See the full article here.

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  • richardmitnick 3:58 pm on September 17, 2014 Permalink | Reply
    Tags: , Laser Technology,   

    From physicsworld: “New plasmonic nanolaser is cavity-free” 

    physicsworld
    physicsworld.com

    Sep 17, 2014
    Tim Wogan

    A new design for a cavity-free nanolaser has been proposed by physicists at Imperial College London. The design builds on a proposal from the same team earlier this year to reduce the group velocity of light of a particular frequency to exactly zero in a metal–dielectric–metal waveguide. The laser, which has yet to be built, makes use of two such zero-velocity regions, and would achieve population inversion and create a laser beam without the need for an optical cavity. The researchers suggest that the design could have important applications in optical telecommunications and computing, as well as theoretical implications in reconciling the physics of lasers with plasmonics.

    graph
    Slowing light to a stop: nanolaser has no cavity

    The traditional design for a laser involves encasing a gain medium such as a gas in a cavity containing two opposing mirrors. The gain medium contains two electronic energy levels, and, in the natural state, the lower energy level is the more populated. However, by injecting electrical or light energy into the cavity, some electrons can be “pumped” into the upper state. At low pumping levels, atoms pushed to the upper level decay spontaneously back to the ground state with the emission of a photon. However, above a certain threshold, transitions back to the ground state are predominantly caused by an excited atom’s absorption of a second photon. The two photons are emitted perfectly in phase, and go on to excite emission from more atoms. The resulting beam of phase-coherent photons is the laser beam.

    Lasers have revolutionized modern science and technology, with tiny lasers can be found everywhere from cheap pointers to state-of-the-art telecommunications systems. While much smaller nanoscale lasers would be useful for creating chip-based optical circuits, the need for a cavity limits means that it is difficult to miniaturize a conventional laser beyond the wavelength of the light it produces. This limit is about one micron for the light used in telecommunications technologies.

    Plasmonic interactions

    Now, Ortwin Hess and colleagues have devised a new way of producing a sub-wavelength laser by removing the cavity altogether. The researchers designed a layered metal–dielectric–metal waveguide structure that supports plasmonic interactions between light and conduction electrons at the metal–dielectric interfaces. Such a plasmonic waveguide supports two “zero-velocity singularities” at closely spaced but distinct frequencies. Light of other frequencies will propagate through the semiconductor very slowly – allowing it plenty of time to interact with the gain material. While slow and stopped light might sound like unphysical concepts, they can occur when light interacts with plasmons. Injecting a pulse of this slow light, the researchers calculated, will pump carriers from a lower energy state to a higher state. This higher state would then decay to an intermediate state, which would then decay to produce the laser light. The presence of the zero-velocity singularities causes the laser light to be trapped in the material, where it drives the desired coherent stimulated emission.

    To produce a laser beam, however, some of the laser light must be able to leave the device. In previous work (see “Plasmonic waveguide stops light in its tracks”), Hess and colleagues proposed exciting a zero-velocity mode by passing the light through the cladding in the form of an evanescent wave – a special type of wave the frequency of which is a complex number. Radiation incident on the cladding would excite an evanescent wave, which would in turn excite the stopped-light mode in the dielectric inside. In their new paper, Hess and colleagues turn this idea on its head and use the evanescent field to allow laser light to escape. By varying the precise properties and thickness of the cladding layer, the proportion of light allowed to escape could be tuned, producing a laser beam of variable intensity.

    Biomedical applications

    Nicholas Fang, a nanophotonics expert at the Massachusetts Institute of Technology, believes that, if such cavity-free nanolasers could be produced, they could have major practical implications not only in computation and signalling, but also in less-obvious fields such as prosthetics: he suggests they could be embedded in synthetic tissue to provide sensors with output signals detectable by the nervous system. “Here you’d have a laser source that could be directly implantable,” he explains.

    Hess, meanwhile, is excited by the potential theoretical implications of the work. While the current research focuses on using plasmonic interactions to produce coherent light, he believes that it should also be possible to keep the plasmons themselves confined within the waveguide to produce a miniature surface plasmon laser or “spaser”.

    The research is described in Nature Communications.

    See the full article here.

    PhysicsWorld is a publication of the Institute of Physics. The Institute of Physics is a leading scientific society. We are a charitable organisation with a worldwide membership of more than 50,000, working together to advance physics education, research and application.

    We engage with policymakers and the general public to develop awareness and understanding of the value of physics and, through IOP Publishing, we are world leaders in professional scientific communications.
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