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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

    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

    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.

    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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  • 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

    17 February 2015
    Alison Abbott

    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.

    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

    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.

    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

    See the full article here.

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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” 


    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.

    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
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    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.

    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.

    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
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    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”

    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.

    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.

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

    Lawrence Livermore National Laboratory

    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.

    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” 


    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.

    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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  • richardmitnick 3:41 pm on August 27, 2014 Permalink | Reply
    Tags: , ELI-Beamlines, Laser Technology, ,   

    From Livermore Lab: “LLNL synchs up with ELI Beamlines on timing system” 

    Lawrence Livermore National Laboratory

    Breanna Bishop, LLNL, (925) 423-9802, bishop33@llnl.gov

    In 2013, Lawrence Livermore National Laboratory (LLNL), through Lawrence Livermore National Security LLC (LLNS), was awarded more than $45 million to develop and deliver a state-of-the-art laser system for the European Union’s Extreme Light Infrastructure Beamlines facility (ELI-Beamlines), under construction in the Czech Republic.

    Thomas Manzec and Marc-Andre Drouin, from ELI Beamlines, work on synchronizing the HAPLS and ELI timing systems. Photo by Jim Pryatel.

    The ELI Beamlines facility is being built on a brownfield site with sufficient infrastructure. According to the current zoning plan, the area can be used for public amenities, science and research. It is therefore a place that provides enough space both for the laser center, as well as for any other building of similar use (technology park buildings, spin-off companies or other research facilities).

    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 petawatt laser system.


    Nearly a year into the project, much progress has been made, and all contract milestones to date have been delivered on schedule. Under the same agreement, ELI Beamlines delivers various work packages to LLNL enabling HAPLS control and timing systems to interface with the overarching ELI Beamlines facility control system. In a collaborative effort, researchers and engineers from LLNL’s NIF & Photon Science Directorate work with scientists from the ELI facility to develop, program and configure these systems.

    National Ignition Facility
    NIF at Livermore

    According to Constantin Haefner, LLNL’s project manager for HAPLS, this joint work is vital. “Working closely together on these collaborative efforts allows us to deliver a laser system most consistent with ELI Beamlines facility requirements. It also allows the ELI-Beamlines team to gain early insight into the laser system architecture and gain operational experience,” he said.

    This summer, that process began. Marc-Andre Drouin and Karel Kasl, control system programmers for ELI, spent three months at LLNL working with the HAPLS integrated control system team. During their time at LLNL, they focused almost exclusively on the ELI-HAPLS timing interface, which allows exact synchronization of HAPLS to the ELI Beamlines master clock.

    “The HAPLS timing system must be able to operate independent of the ELI timing system,” Drouin said. “But, it also needs to be capable of being perfectly synchronized to ELI. That bridge between timing systems is what we have been working on – making sure HAPLS runs very well independently as well as integrating with ELI.”

    Haefner pointed out that while HAPLS is a major component, it becomes a subsystem when it moves to the ELI facility. Once at ELI, HAPLS will integrate with the wider user facility, consisting of target systems, experimental systems, diagnostic systems – all of which have to be timed and fed from a master clock.

    Kasl likened the master clock to a universal clock used by an office. “We brought the clock here, and now everyone in the office is using the clock to synchronize their work,” he said.

    The master clock, built by ELI, was programmed as a bridge between the ELI and HAPLS timing systems. During their time at LLNL, Drouin and Kasl worked on configuring that hardware and writing the software that talks to the clock and to the subcomponents that control a very precise sequence of events.

    Last week, the ELI team finished their three-month stint at LLNL, but will be back in early fall to continue work – and they’re looking forward to it.

    “This unit is going to get integrated with our other systems, so there needs to be an overlap between the two teams,” Kasl said.

    “It’s good experience for us to learn about the internal workings of the HAPLS system,” Drouin added. “Having this inside knowledge of the most integral parts of the laser is a very big advantage for us in the long run.”

    Earlier this year, Jack Naylon and Tomas Mazanec, also from ELI, visited LLNL to contribute to the work.

    See the full article here.

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  • richardmitnick 3:28 pm on August 23, 2014 Permalink | Reply
    Tags: , , Electrical Engineering, Laser Technology,   

    From Princeton: “Laser device may end pin pricks, improve quality of life for diabetics” 

    Princeton University
    Princeton University

    August 20, 2014
    John Sullivan, Office of Engineering Communications

    Princeton University researchers have developed a way to use a laser to measure people’s blood sugar, and, with more work to shrink the laser system to a portable size, the technique could allow diabetics to check their condition without pricking themselves to draw blood.

    “We are working hard to turn engineering solutions into useful tools for people to use in their daily lives,” said Claire Gmachl, the Eugene Higgins Professor of Electrical Engineering and the project’s senior researcher. “With this work we hope to improve the lives of many diabetes sufferers who depend on frequent blood glucose monitoring.”

    In an article published June 23 in the journal Biomedical Optics Express, the researchers describe how they measured blood sugar by directing their specialized laser at a person’s palm. The laser passes through the skin cells, without causing damage, and is partially absorbed by the sugar molecules in the patient’s body. The researchers use the amount of absorption to measure the level of blood sugar.

    Sabbir Liakat, the paper’s lead author, said the team was pleasantly surprised at the accuracy of the method. Glucose monitors are required to produce a blood-sugar reading within 20 percent of the patient’s actual level; even an early version of the system met that standard. The current version is 84 percent accurate, Liakat said.

    “It works now but we are still trying to improve it,” said Liakat, a graduate student in electrical engineering.

    A new system developed by Princeton researchers uses a laser to allow diabetics to check their blood sugar without pricking their skin. Members of the research team included, from left, Sabbir Liakat, a graduate student in electrical engineering; Claire Gmachl, the Eugene Higgins Professor of Electrical Engineering; and Kevin Bors, who graduated in 2013 with a degree in electrical engineering. (Photos by Frank Wojciechowski for the Office of Engineering Communications)

    When the team first started, the laser was an experimental setup that filled up a moderate-sized workbench. It also needed an elaborate cooling system to work. Gmachl said the researchers have solved the cooling problem, so the laser works at room temperature. The next step is to shrink it.

    “This summer, we are working to get the system on a mobile platform to take it places such as clinics to get more measurements,” Liakat said. “We are looking for a larger dataset of measurements to work with.”

    The key to the system is the infrared laser’s frequency. What our eyes perceive as color is created by light’s frequency (the number of light waves that pass a point in a certain time). Red is the lowest frequency of light that humans normally can see, and infrared’s frequency is below that level. Current medical devices often use the “near-infrared,” which is just beyond what the eye can see. This frequency is not blocked by water, so it can be used in the body, which is largely made up of water. But it does interact with many acids and chemicals in the skin, so it makes it impractical to use for detecting blood sugar.

    Mid-infrared light, however, is not as much affected by these other chemicals, so it works well for blood sugar. But mid-infrared light is difficult to harness with standard lasers. It also requires relatively high power and stability to penetrate the skin and scatter off bodily fluid. (The target is not the blood but fluid called dermal interstitial fluid, which has a strong correlation with blood sugar.)

    The breakthrough came from the use of a new type of device that is particularly adept at producing mid-infrared frequencies — a quantum cascade laser.

    The new monitor uses a laser, instead of blood sample, to read blood sugar levels. The laser is directed at the person’s palm, passes through skin cells and is partially absorbed by sugar molecules, allowing researchers to calculate the level of blood sugar.

    In many lasers, the frequency of the beam depends on the material that makes up the laser — a helium-neon laser, for example, produces a certain frequency band of light. But in a quantum cascade laser, in which electrons pass through a “cascade” of semiconductor layers, the beam can be set to one of a number of different frequencies. The ability to specify the frequency allowed the researchers to produce a laser in the mid-infrared region. Recent improvements in quantum cascade lasers also provided for increased power and stability needed to penetrate the skin.

    To conduct their experiment, the researchers used the laser to measure the blood sugar of three healthy people before and after they each ate 20 jellybeans, which raise blood sugar levels. The researchers also checked the measurements with a finger-prick test. They conducted the measurements repeatedly over several weeks.

    The researchers said their results indicated that the laser measurements readings produced average errors somewhat larger than the standard blood sugar monitors, but remained within the clinical requirement for accuracy.

    “Because the quantum cascade laser can be designed to emit light across a very wide wavelength range, its usability is not just for glucose detection, but could conceivably be used for other medical sensing and monitoring applications,” Gmachl said.

    Besides Liakat and Gmachl, researchers included Kevin Bors, Class of 2013, Laura Xu, Class of 2015, and Callie Woods, Class of 2014, who worked on the project as undergraduate students majoring in electrical engineering; and Jessica Doyle, a teacher at Hunterdon Regional Central High School.

    Support for the research was provided in part by the Wendy and Eric Schmidt Foundation, the National Science Foundation, Daylight Solutions Inc., and Opto-Knowledge Systems. The research involving human subjects was conducted according to regulations set by the Princeton University Institutional Review Board.

    See the full article here.

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    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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