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  • richardmitnick 8:06 pm on July 17, 2014 Permalink | Reply
    Tags: , , , Laser Technology, ,   

    From SLAC Lab: “X-ray Laser Measures Leaping Electrons” 

    SLAC Lab

    July 17, 2014
    SLAC Experiment Provides New Insight About How Electrons Move Across Molecules

    Many chemical reactions – such as those at work in batteries and photosynthesis – rely on electrons moving from one atom or molecule to another. Now, scientists have directly measured the movement of electrons as they leap across parts of the same molecule, which provides useful insight about the mechanisms involved in forming and breaking chemical bonds.

    The experiment took place at SLAC’s Linac Coherent Light Source (LCLS) X-ray laser, a DOE Office of Science user facility. Scientists split molecules with pulses of infrared light and then hit them with intense X-ray pulses to drive and study the transfer of electrons between the fragments. The experiment showed that the electrons can travel surprisingly long distances – up to 10 times the length of the original, intact molecule – to jump the gap. The results are published in the July 18 issue of Science.

    “This is a clean example of a very important charge-transfer process that can only be resolved using a tool like LCLS,” said Artem Rudenko of Kansas State University, who led the experiment. The knowledge gained in the experiment may ultimately help to explain mechanisms of electron transfer in more complex molecules, including biological samples. This is also central to understanding how X-rays can damage samples and obscure X-ray images.

    As a basic form of chemical reaction, electron transfer is vital to many life processes. The 1992 Nobel Prize in Chemistry recognized pioneering theoretical work in electron transfer that has underpinned many related chemistry experiments.

    The team studied methyl iodide molecules, also known as iodomethane, which break in a predictable way when hit by intense infrared light: One fragment contains a single iodine atom, the other has carbon and hydrogen atoms.

    In this illustration of a severed methyl iodide molecule, electrons jump the gap from one fragment containing carbon and hydrogen atoms (right) to the other fragment, which contains an iodine atom (left). Researchers used SLAC’s Linac Coherent Light Source X-ray laser to stimulate and measure the electron-transfer process. (SLAC National Accelerator Laboratory) “>In this illustration of a severed methyl iodide molecule, electrons jump the gap from one fragment containing carbon and hydrogen atoms (right) to the other fragment, which contains an iodine atom (left). Researchers used SLAC’s Linac Coherent Light Source X-ray laser to stimulate and measure the electron-transfer process. (SLAC National Accelerator Laboratory)

    They tuned the LCLS X-ray pulses to knock out electrons only from the iodine atoms, creating a positive charge that attracts electrons from the other fragment to fill the vacancies. As the fragments drift, the gap that electrons jump to reach the iodine atoms widens until it becomes too far for them to reach.

    The researchers varied the timing of the X-ray pulses to tune the distance electrons had to jump to cross this gap. They used time- and position-sensitive detectors to determine the final charge and energy of the fragments, which told them where the remaining electrons ended up. While LCLS X-ray laser pulses are ultrashort, lasting just quadrillionths of a second, or femtoseconds, the electron-transfer process typically spans less than a single femtosecond, Rudenko noted. During this very short time, the distance between the fragments does not change, allowing researchers to more easily gauge the electron movement.

    “With each pair of infrared and X-ray pulses we tried to look at just one molecule,” said Benjamin Erk of Germany’s DESY lab, who analyzed the data. “We traced essentially all of the fragments produced to give us a microscopic ‘picture’ of a single fracture event.” Researchers collected data from about 800,000 fractured molecules.

    The same team, which was also led by Daniel Rolles of DESY, has already conducted follow-up research on other molecules at LCLS, and researchers said it may be possible to study biological compounds found in DNA and RNA, as an example, using the same method. They hope to directly measure the time it takes for the electrons to move across larger and more complex molecules, Rudenko said.

    In addition to researchers from Kansas State University, DESY and SLAC, other collaborating researchers were from the Center for Free-Electron Laser Science, Max Planck Institute for Nuclear Physics, Max Planck Institute for Medical Research, University of Hamburg and Physikalisch-Technische Bundesanstalt (National Metrology Institute), all in Germany; and from Sorbonne University and the French National Center for Scientific Research in France.

    The work was supported by the Max Planck Society, which funded the development and operation of the CAMP instrument used in the experiment; the U.S. Department of Energy Office of Science; the Kansas NSF EPSCoR “First Award” program; the Young Investigator Program of the Helmholtz Association; and the German Research Foundation’s Hamburg Center for Ultrafast Imaging – Structure, Dynamics and Control of Matter at the Atomic Scale.

    See the full article here.

    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

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  • richardmitnick 7:46 pm on July 17, 2014 Permalink | Reply
    Tags: , , Laser Technology, Quartz technology   

    From Caltech: “Future Electronics May Depend on Lasers, Not Quartz” 

    Caltech Logo

    Jessica Stoller-Conrad

    Nearly all electronics require devices called oscillators that create precise frequencies—frequencies used to keep time in wristwatches or to transmit reliable signals to radios. For nearly 100 years, these oscillators have relied upon quartz crystals to provide a frequency reference, much like a tuning fork is used as a reference to tune a piano. However, future high-end navigation systems, radar systems, and even possibly tomorrow’s consumer electronics will require references beyond the performance of quartz.

    Vahala’s new laser frequency reference (left) is a small 6 mm disk; the quartz “tuning fork” (middle) is the frequency reference commonly used today in wristwatches to set the second. The dime (right) is for scale.
    Credit: Jiang Li/Caltech

    Now, researchers in the laboratory of Kerry Vahala, the Ted and Ginger Jenkins Professor of Information Science and Technology and Applied Physics at Caltech, have developed a method to stabilize microwave signals in the range of gigahertz, or billions of cycles per second—using a pair of laser beams as the reference, in lieu of a crystal.

    Quartz crystals “tune” oscillators by vibrating at relatively low frequencies—those that fall at or below the range of megahertz, or millions of cycles per second, like radio waves. However, quartz crystals are so good at tuning these low frequencies that years ago, researchers were able to apply a technique called electrical frequency division that could convert higher-frequency microwave signals into lower-frequency signals, and then stabilize these with quartz.

    The new technique, which Vahala and his colleagues have dubbed electro-optical frequency division, builds off of the method of optical frequency division, developed at the National Institute of Standards and Technology more than a decade ago. “Our new method reverses the architecture used in standard crystal-stabilized microwave oscillators—the ‘quartz’ reference is replaced by optical signals much higher in frequency than the microwave signal to be stabilized,” Vahala says.

    Jiang Li—a Kavli Nanoscience Institute postdoctoral scholar at Caltech and one of two lead authors on the paper, along with graduate student Xu Yi—likens the method to a gear chain on a bicycle that translates pedaling motion from a small, fast-moving gear into the motion of a much larger wheel. “Electrical frequency dividers used widely in electronics can work at frequencies no higher than 50 to 100 GHz. Our new architecture is a hybrid electro-optical ‘gear chain’ that stabilizes a common microwave electrical oscillator with optical references at much higher frequencies in the range of terahertz or trillions of cycles per second,” Li says.

    The optical reference used by the researchers is a laser that, to the naked eye, looks like a tiny disk. At only 6 mm in diameter, the device is very small, making it particularly useful in compact photonics devices—electronic-like devices powered by photons instead of electrons, says Scott Diddams, physicist and project leader at the National Institute of Standards and Technology and a coauthor on the study.

    “There are always tradeoffs between the highest performance, the smallest size, and the best ease of integration. But even in this first demonstration, these optical oscillators have many advantages; they are on par with, and in some cases even better than, what is available with widespread electronic technology,” Vahala says.

    The new technique is described in a paper that will be published in the journal Science on July 18. Other authors on this paper include Hansuek Lee, who is a visiting associate at Caltech. The work was sponsored by the DARPA’s ORCHID and PULSE programs; the Caltech Institute for Quantum Information and Matter (IQIM), an NSF Physics Frontiers Center with support of the Gordon and Betty Moore Foundation; and the Caltech Kavli NanoScience Institute.

    See the full article here.

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 9:13 am on June 11, 2014 Permalink | Reply
    Tags: , , , Fiber technology, , Laser Technology, ,   

    From CERN: “Laser acceleration, now with added fibre” 

    CERN New Masthead

    8 Jan 2013 [Where has this been?]
    Cian O’Luanaigh

    The International Coherent Amplification Network (ICAN) is studying the potential of lasers for collision physics. CERN is a beneficiary of the project and will collaborate with 15 other institutes from around the world, including KEK in Japan, Fermilab in the USA, and DESY in Germany. “The network is looking into existing fibre laser technology, which we believe has fantastic potential for accelerators,” says Gerard Mourou, ICAN co-ordinator at the École Polytechnique in France. “The hope is to make laser acceleration competitive with traditional radio-frequency acceleration techniques.”


    Laser acceleration is currently limited by the “single-shot” nature of the technology. As there is no way to remove the excess heat created by lasers, they cannot be sustained for high-energy acceleration. However, using fibre lasers may resolve this issue. By using laser diodes to pump the laser through typical optical fibres, fibre lasers absorb the heat created, thus giving fibre lasers very high repetition rates. This, in turn, may allow the laser to be sustained long enough to accelerate particles into collisions. Fibres should also improve the overall power efficiency of lasers by 35-40%, making them more economically feasible for experiments. “ICAN is studying whether we can turn the potential of fibre lasers into feasible technology,” says Gerard. “Once we have achieved this, we can then look at direct laser applications for accelerators.”

    “CERN accelerator experts will advise collaborating institutions to define the requirements useful for collision physics,” says Jean-Pierre Koutchouk, CERN advisor for international relations in accelerators and technology. “CERN’s contribution to the ICAN project is part of a wider strategy to encourage the development of laser acceleration technologies. By supporting ICAN and similar research projects, CERN will be contributing to the R&D of potentially ground-breaking accelerator technologies.”

    ICAN is only the beginning and, if all goes as expected, we will be seeing more accelerator projects based on fibre lasers. “We’re considering ICAN as an 18-month-long preparatory phase, vetting the laser technology for a possible longer project based on ICAN laser concepts,” concludes Gerard.

    The ICAN kick-off meeting was held at CERN on 22 February 2012. The network has received half a million euros in the framework of the FP7 Capacities programme.

    See the full article here.

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  • richardmitnick 1:57 pm on May 28, 2014 Permalink | Reply
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    From Berkeley Lab: “A Path Toward More Powerful Tabletop Accelerators” 

    Berkeley Logo

    Berkeley Lab

    May 28, 2014
    Kate Greene kgreene@lbl.gov

    Making a tabletop particle accelerator just got easier. A new study shows that certain requirements for the lasers used in an emerging type of small-area particle accelerator can be significantly relaxed. Researchers hope the finding could bring about a new era of accelerators that would need just a few meters to bring particles to great speeds, rather than the many kilometers required of traditional accelerators. The research, from scientists at the U.S. Department of Energy’s (DOE) Lawrence Berkeley National Laboratory (Berkeley Lab), is presented as the cover story in the May special issue of Physics of Plasmas.

    Traditional accelerators, like the Large Hadron Collider where the Higgs boson was recently discovered, rely on high-power radio-frequency waves to energize electrons. The new type of accelerator, known as a laser-plasma accelerator, uses pulses of laser light that blast through a soup of charged particles known as a plasma; the resulting plasma motion, which resemble waves in water, accelerates electrons riding atop the waves to high speeds.

    3D Map of the longitudinal wakefield generated by the incoherent combination of 208 low-energy laser beamlets. In the region behind the driver, the wakefield is regular. Credit: Carlo Benedetti, Berkeley Lab

    The problem, however, is creating a laser pulse that’s powerful enough to compete with the big accelerators. In particular, lasers need to have the capability to fire a high-energy pulse thousands of times a second. Today’s lasers can only manage one pulse per second at the needed energy levels.

    “If you want to make a device that’s of use for particle physics, of use for medical applications, of use for light source applications, you need repetition rate,” explains Wim Leemans, physicist at Berkeley Lab. In January of 2013, the DOE held a workshop on laser technology for accelerators. At the time, says Leemans, the big question was how to get from the current technology to the scaled up version.

    Conventional wisdom holds that many smaller lasers, combined in a particular way, could essentially create one ultra powerful pulse. In theory, this sounds fine, but the practical requirements to build such a system have seemed daunting. For instance, it was believed that the light from the smaller lasers would need to be precisely matched in color, phase, and other properties in order to produce the electron-accelerating motion within the plasma. “We thought this was really challenging,” says Leemans, “We thought, you need this nice laser pulse, and everything needs to be done properly to control the laser pulse.”

    But the new Berkeley Lab study has found this isn’t the case. Paper co-authors Carlo Benedetti, Carl Schroeder, Eric Esarey and Leemans wanted to see what an erratic laser pulse would actually do inside a plasma. Guided by theory and using computer simulations to test various scenarios, the researchers looked at how beams of various colors and phases—basically a hodgepodge of laser light—affected the plasma. They soon discovered, no matter the beam, the plasma didn’t care.

    “The plasma is a medium that responds to a laser, but it doesn’t respond immediately,” says Benedetti, a physicist at Berkeley Lab. The light is just operating on a faster time scale and a smaller length scale, he explains. All of the various interference patterns and various electromagnetic fields average out in the slow-responding plasma medium. In other words, once laser light gets inside the plasma, many of the problems disappear.

    “As an experimentalist for all these years we’re trying to make these perfect laser pulses, and maybe we didn’t need to worry so much,” says Leemans. “I think this will have a big impact on the laser community and laser builders because all of a sudden, they’ll think of approaches where before hand all of us said, ‘No, no, no. You can’t do that.’ This new result says, well maybe you don’t have to be all that careful.”

    Leemans says the ball is back in the experimentalists’ and laser builders’ court to prove that the idea can work. In 2006, he and his team demonstrated a three-centimeter long plasma accelerator. Where a traditional accelerator can take kilometers to drive an electron to 50 giga-electron volts (GeV), Leemans and team showed that a mini-laser plasma accelerator could get electrons to 1 GeV in just three centimeters with a laser pulse of about 40 terawatt. To go to higher electron energies, in 2012, a larger more powerful laser was installed at the Berkeley Lab Laser Accelerator (BELLA) facility with a petawatt pulse (1 quadrillion watts) that lasts 40 femtoseconds, which is now being used in experiments that aim at generating a 10 GeV beam.

    Still, the goal of a high-repetition rate, 10-GeV laser-plasma accelerator that fires a thousand pulses or more per second, is at least five to ten years away, says Leemans. But a new project called k-BELLA (k is for kilohertz) is in the works that will use the principles of combined, messy laser light sources to produce fast, more powerful laser pulses. “Once we synthesize a pulse at higher repetition rates,” says Leemans, “we will be on our way towards a kilohertz GeV laser plasma accelerator.”

    This work was supported by the DOE Office of Science and used the facilities of the National Energy Research Scientific Computing Center (NERSC) located at Berkeley Lab.

    1. # #

    See the full article here.

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

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  • richardmitnick 10:10 pm on April 16, 2014 Permalink | Reply
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    From SLAC Lab: “Scientists Capture Ultrafast Snapshots of Light-driven Superconductivity” 

    April 16, 2014
    No Writer Credit

    A new study pins down a major factor behind the appearance of superconductivity – the ability to conduct electricity with 100 percent efficiency – in a promising copper-oxide material.

    Scientists used carefully timed pairs of laser pulses at SLAC National Accelerator Laboratory’s Linac Coherent Light Source (LCLS) to trigger superconductivity in the material and immediately take X-ray snapshots of its atomic and electronic behavior as superconductivity emerged.

    The Undulator Hall at SLAC’s Linac Coherent Light Source X-ray laser. (Brad Plummer/SLAC)

    They discovered that so-called “charge stripes” of increased electrical charge melted away as superconductivity appeared. Further, the results help rule out the theory that shifts in the material’s atomic lattice hinder the onset of superconductivity.

    Armed with this new understanding, scientists may be able to develop new techniques to eliminate these charge stripes and help pave the way for room-temperature superconductivity, often considered the holy grail of condensed matter physics. The demonstrated ability to rapidly switch between the insulating and superconducting states could also prove useful in advanced electronics and computation.

    The results, from a collaboration led by scientists from the Max Planck Institute for the Structure and Dynamics of Matter in Germany and the U.S. Department of Energy’s SLAC and Brookhaven national laboratories, were published online April 16, 2014, in the journal Physical Review Letters.

    “The very short timescales and the need for high spatial resolution made this experiment extraordinarily challenging,” said co-author Michael Först, a scientist at the Max Planck Institute. “Now, using femtosecond X-ray pulses, we found a way to capture the quadrillionths-of-a-second dynamics of the charges and the crystal lattice. We’ve broken new ground in understanding light-induced superconductivity.”

    Josh Turner, an LCLS staff scientist, said, “This represents a very important result in the field of superconductivity using LCLS. It demonstrates how we can unravel different types of complex mechanisms in superconductivity that have, up until now, been inseparable.”

    He added, “To make this measurement, we had to push the limits of our current capabilities. We had to measure a very weak, barely detectable signal with state-of-the-art detectors, and we had to tune the number of X-rays in each laser pulse to see the signal from the stripes without destroying the sample.”

    Ripples in Quantum Sand

    The compound used in this study was a layered material consisting of lanthanum, barium, copper, and oxygen grown at Brookhaven Lab by physicist Genda Gu. Each copper oxide layer contained the crucial charge stripes.

    Physicist Genda Gu in the Brookhaven Lab facility where the copper-oxide materials were grown for this study.

    “Imagine these stripes as ripples frozen in the sand,” said John Hill, a Brookhaven Lab physicist and coauthor on the study. “Each layer has all the ripples going in one direction, but in the neighboring layers they run crosswise. From above, this looks like strings in a pile of tennis racquets. We believe that this pattern prevents each layer from talking to the next, thus frustrating superconductivity.”

    To excite the material and push it into the superconducting phase, the scientists used mid-infrared laser pulses to “melt” those frozen ripples. These pulses had previously been shown to induce superconductivity in a related compound at a frigid 10 Kelvin (minus 442 degrees Fahrenheit).

    “The charge stripes disappeared immediately,” Hill said. “But specific distortions in the crystal lattice, which had been thought to stabilize these stripes, lingered much longer. This shows that only the charge stripes inhibit superconductivity.”

    Stroboscopic Snapshots

    To capture these stripes in action, the collaboration turned to SLAC’s LCLS X-ray laser, which works like a camera with a shutter speed faster than 100 femtoseconds, or quadrillionths of a second, and provides atomic-scale image resolution. LCLS uses a section of SLAC’s 2-mile-long linear accelerator to generate the electrons that give off X-ray light.

    Researchers used the so-called “pump-probe” approach: an optical laser pulse strikes and excites (pumps) the lattice and an ultrabright X-ray laser pulse is carefully synchronized to follow within femtoseconds and measure (probe) the lattice and stripe configurations. Each round of tests results in some 20,000 X-ray snapshots of the changing lattice and charge stripes, a bit like a strobe light rapidly illuminating the process.

    To measure the changes with high spatial resolution, the team used a technique called resonant soft X-ray diffraction. The LCLS X-rays strike and scatter off the crystal into the detector, carrying time-stamped signatures of the material’s charge and lattice structure that the physicists then used to reconstruct the rise and fall of superconducting conditions.

    “By carefully choosing a very particular X-ray energy, we are able to emphasize the scattering from the charge stripes,” said Brookhaven Lab physicist Stuart Wilkins, another co-author on the study. “This allows us to single out a very weak signal from the background.”

    Toward Superior Superconductors

    The X-ray scattering measurements revealed that the lattice distortion persists for more than 10 picoseconds (trillionths of a second) – long after the charge stripes melted and superconductivity appeared, which happened in less than 400 femtoseconds. Slight as it may sound, those extra trillionths of a second make a huge difference.

    “The findings suggest that the relatively weak and long-lasting lattice shifts do not play an essential role in the presence of superconductivity,” Hill said. “We can now narrow our focus on the stripes to further pin down the underlying mechanism and potentially engineer superior materials.”

    Andrea Cavalleri, director of the Max Planck Institute, said, “Light-induced superconductivity was only recently discovered, and we’re already seeing fascinating implications for understanding it and going to higher temperatures. In fact, we have observed the signature of light-induced superconductivity in materials all the way up to 300 Kelvin (80 degrees Fahrenheit) – that’s really a significant breakthrough that warrants much deeper investigations.”

    Other collaborators on this research include the University of Groningen, the University of Oxford, Diamond Light Source, the Lawrence Berkeley National Laboratory, Stanford University, the European XFEL, the University of Hamburg and the Center for Free-Electron Laser Science.

    The research conducted at the Soft X-ray Materials Science (SXR) experimental station at SLAC’s LCLS – a DOE Office of Science user facility – was funded by Stanford University, Lawrence Berkeley National Laboratory, the University of Hamburg and the Center for Free-Electron Laser Science (CFEL). Work performed at Brookhaven Lab was supported by the DOE’s Office of Science.

    See the full article here.

    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

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  • richardmitnick 1:11 pm on March 31, 2014 Permalink | Reply
    Tags: , , Laser Technology,   

    From Ames Lab: “Ultra-fast laser spectroscopy lights way to understanding new materials” 

    Ames Laboratory

    Feb. 28, 2014
    Jigang Wang, Material Sciences and Engineering, 515-294-5630
    Breehan Gerleman Lucchesi, Public Affairs, 515-294-9750

    Scientists at the U.S. Department of Energy’s Ames Laboratory are revealing the mysteries of new materials using ultra-fast laser spectroscopy, similar to high-speed photography where many quick images reveal subtle movements and changes inside the materials. Seeing these dynamics is one emerging strategy to better understanding how new materials work, so that we can use them to enable new energy technologies.

    Physicist Jigang Wang and his colleagues recently used ultra-fast laser spectroscopy to examine and explain the mysterious electronic properties of iron-based superconductors. Results appeared in Nature Communications this month.

    Superconductors are materials that, when cooled below a certain temperature, display zero electrical resistance, a property that could someday make possible lossless electrical distribution. Superconductors start in a “normal” often magnetic state and then transition to a superconducting state when they are cooled to a certain temperature.

    What is still a mystery is what goes on in materials as they transform from normal to superconducting. And this “messy middle” area of superconducting materials’ behavior holds richer information about the why and how of superconductivity than do the stable areas.

    Ames Laboratory scientists use ultra-fast laser spectroscopy to “see” tiny actions in real time in
    materials. Scientists apply a pulse laser to a sample to excite the material. Some of the laser light
    is absorbed by the material, but the light that passes through or reflected from the material can be
    used to take super-fast “snapshots” of what is going on in the material following the laser pulse.

    “The stable states of materials aren’t quite as interesting as the crossover region when comes to understanding materials’ mechanisms because everything is settled and there’s not a lot of action. But, in this crossover region to superconductivity, we can study the dynamics, see what goes where and when, and this information will tell us a lot about the interplay between superconductivity and magnetism,” said Wang, who is also an associate professor of physics and astronomy at Iowa State University.

    But the challenges is that in the crossover region, all the different sets of materials properties that scientists examine, like its magnetic order and electronic order, are all coupled. In other words, when there’s a change to one set of properties, it changes all the others. So, it’s really difficult to trace what individual changes and properties are dominant.

    The complexity of this coupled state has been studied by groundbreaking work by research groups at Ames Laboratory over the past five years. Paul Canfield, an Ames Laboratory scientist and expert in designing and developing iron-based superconductor materials, created and characterized a very high quality single crystal used in this investigation. These high-quality single crystals had been exceptionally well characterized by other techniques and were essentially “waiting for their close up” under Wang’s ultra-fast spot-light.

    Wang and the team used ultra-fast laser spectroscopy to “see” the tiny actions in materials. In ultra-fast laser spectroscopy, scientists apply a pulsed laser to a materials sample to excite particles within the sample. Some of the laser light is absorbed by the material, but the light that passes through the material can be used to take super-fast “snapshots” of what is going on in the material following the laser pulse and then replayed afterward like a stop-action movie.

    The technique is especially well suited to understanding the crossover region of iron-arsenide based superconductors materials because the laser excitation alters the material so that different properties of the material are distinguishable from each other in time, even the most subtle evolutions in the materials’ properties.

    “Ultra-fast laser spectroscopy is a new experimental tool to study dynamic, emergent behavior in complex materials such as these iron-based superconductors,” said Wang. “Specifically, we answered the pressing question of whether an electronically-driven nematic order exists as an independent phase in iron-based superconductors, as these materials go from a magnetic normal state to superconducting state. The answer is yes. This is important to our overall understanding of how superconductors emerge in this type of materials.”

    Aaron Patz and Tianqi Li collaborated on the laser spectroscopy work. Sheng Ran, Sergey L. Bud’ko and Paul Canfield collaborated on sample development at Ames Laboratory and Iowa State University. Rafael M. Fernandes at the University of Minnesota, Joerg Schmalian, formerly of Ames Laboratory and now at Karlsruhe Institute of Technology and Ilias E. Perakis at University of Crete, Greece collaborated on the simulation work.

    Wang, Patz, Li, Ran, Bud’ko and Canfield’s work at Ames Laboratory was supported by the U.S. Department of Energy’s Office of Science, (sample preparation and characterization). Wang’s work on pnictide superconductors is supported by Ames Laboratory’s Laboratory Directed Research and Development (LDRD) funding (femtosecond laser spectroscopy).

    DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science website at science.energy.gov/.

    See the full article here.

    Ames Laboratory is a government-owned, contractor-operated research facility of the U.S. Department of Energy that is run by Iowa State University.

    For more than 60 years, the Ames Laboratory has sought solutions to energy-related problems through the exploration of chemical, engineering, materials, mathematical and physical sciences. Established in the 1940s with the successful development of the most efficient process to produce high-quality uranium metal for atomic energy, the Lab now pursues a broad range of scientific priorities.

    Ames Laboratory shares a close working relationship with Iowa State University’s Institute for Physical Research and Technology, or IPRT, a network of scientific research centers at Iowa State University, Ames, Iowa.

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  • richardmitnick 3:30 pm on March 25, 2014 Permalink | Reply
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    From SLAC Lab: “A New Way to Tune X-ray Laser Pulses” 

    [New policies at SLAC are resulting in my bringing the lab's news later than necessary. SLAC is working on improving the situation.]

    March 10, 2014
    Glenn Roberts Jr.

    A new system at SLAC National Accelerator Laboratory’s X-ray laser narrows a rainbow spectrum of X-ray colors to a more intense band of light, creating a much more powerful way to view fine details in samples at the scale of atoms and molecules.

    “It’s like going from regular television to HDTV,” said Norbert Holtkamp, SLAC deputy director and leader of the lab’s Accelerator Directorate.

    Designed and installed at SLAC’s Linac Coherent Light Source (LCLS) in collaboration with Lawrence Berkeley National Laboratory and Switzerland’s Paul Scherrer Institute, it is the world’s first “self-seeding” system for enhancing lower-energy or “soft” X-rays.

    Scientists had to overcome a series of engineering challenges to build it, and it is already drawing international interest for its potential use at other X-ray free-electron lasers.

    “Because this system delivers more intense soft X-ray light at the precise energy we want for experiments, we can make measurements at a far faster rate,” said Bill Schlotter, an LCLS staff scientist. “It will open new possibilities, from exploring exotic materials and biological and chemical samples in greater detail to improving our view of the behavior of atoms and molecules.”

    Cutting Through the Noise

    LCLS’s laser pulses vary in intensity and color, and this randomness or “noise,” like fuzzy reception on a TV, sometimes complicates experiments and data analysis. Self-seeding cuts through this noise by providing a stronger and more consistent intensity peak within each laser pulse.

    “We’re taking something that’s in a range of colors and trying to select a single color and pack as much power in as we can,” said Daniel Ratner, an associate staff scientist at SLAC and lead scientist on the project. “We’re going from the randomness of a typical pulse to a nice, clean, narrow profile that is well-understood.”

    Scientists had installed another self-seeding system at LCLS in 2012 for higher-energy “hard” X-rays. It has been put to use in studies of matter under extreme temperatures and pressures, the structure of biological molecules and electron motions in materials, for example.

    Extending self-seeding to soft X-rays was a logical next step. LCLS scientists Yiping Feng, Daniele Cocco and others designed a compact X-ray optics system that was key to the success of the project, which was led by SLAC’s Jerry Hastings and Zhirong Huang.

    The team achieved self-seeding with soft X-rays in December, and conducted follow-up tests in January and February. They are working to improve the system and to make it available to visiting scientists.

    LCLS X-ray pulses are powered by an electron beam from SLAC’s linear accelerator. The electrons wiggle through a series of powerful magnets, called undulators. This forces them to emit X-ray light, and that light grows in intensity as it moves through the undulator chain.

    SLAC Linear Accelerator
    SLAC Linear Accelerator

    The new system, installed about a quarter of the way down the undulator chain, diverts a narrow, purified slice of the X-ray laser light and briefly and precisely overlaps it with the beam of electrons traveling through the undulators. This produces a “seed” – a spike of high-intensity light in a single color – that is amplified as the X-ray pulses move through the remaining undulators toward LCLS experimental stations.

    Engineering Challenge

    “A big technical challenge was to fit everything in one 13-foot-long undulator section,” including a complex network of cabling, optics, magnets and mechanical systems, said SLAC’s Paul Montanez, project manager and lead engineer for the system. “A tremendous number of people pulled this project together, from administrative, technical and professional staff to scientists.”

    A view of the soft X-ray self-seeding system during installation in the Undulator Hall at SLAC’s Linac Coherent Light Source X-ray laser. (Brad Plummer/SLAC)

    Ziga Oven monitors the installation of the soft X-ray self-seeding system in the Undulator Hall at SLAC’s Linac Coherent Light Source X-ray laser. (Brad Plummer/SLAC)

    The Berkeley Lab team designed and built the hardware that diverts and refines the X-ray light, as well as mechanical systems that align the X-rays and electrons, adjust the X-ray energy and retract components out of the path of X-rays when not in use. The Paul Scherrer team designed and built the optical equipment for the system. SLAC was responsible for integrating the components and building the controls that automate the system.

    “This project was pretty challenging in that we were designing and developing and installing this equipment in an operating facility, with little time for the actual installation,” said Ken Chow, the lead engineer for the Berkeley Lab effort. He noted that the project required many custom parts, such as a movable mirror that must rotate with incredible precision – “It’s like taking a meter stick and moving one end one-half millionth of a meter,” he said.

    Next Steps

    SLAC scientists are hoping to use the seeding system, coupled with an intricate tuning of the magnets in the undulators, to produce even higher-intensity pulses for the next generation of X-ray lasers.

    Already, collaborators from the Paul Scherrer Institute are considering a similar self-seeding system for a planned soft X-ray laser in Switzerland, and there has been great interest in such a system for other X-ray laser projects in the works.

    “We would like to learn and profit from this for our own project, the SwissFEL,” said Uwe Flechsig, who led the Paul Scherrer team that was responsible for delivering the system’s optics.

    See the full article here.

    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

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  • richardmitnick 2:49 pm on February 20, 2014 Permalink | Reply
    Tags: , , , Laser Technology   

    From Caltech: “A New Laser for a Faster Internet” 

    Caltech Logo

    Jessica Stoller-Conrad

    A new laser developed by a research group at Caltech holds the potential to increase by orders of magnitude the rate of data transmission in the optical-fiber network—the backbone of the Internet.

    The study was published the week of February 10–14 in the online edition of the Proceedings of the National Academy of Sciences. The work is the result of a five-year effort by researchers in the laboratory of Amnon Yariv, Martin and Eileen Summerfield Professor of Applied Physics and professor of electrical engineering; the project was led by postdoctoral scholar Christos Santis (PhD ’13) and graduate student Scott Steger.Light is capable of carrying vast amounts of information—approximately 10,000 times more bandwidth than microwaves, the earlier carrier of long-distance communications. But to utilize this potential, the laser light needs to be as spectrally pure—as close to a single frequency—as possible. The purer the tone, the more information it can carry, and for decades researchers have been trying to develop a laser that comes as close as possible to emitting just one frequency.

    No image Credit

    Today’s worldwide optical-fiber network is still powered by a laser known as the distributed-feedback semiconductor (S-DFB) laser, developed in the mid 1970s in Yariv’s research group. The S-DFB laser’s unusual longevity in optical communications stemmed from its, at the time, unparalleled spectral purity—the degree to which the light emitted matched a single frequency. The laser’s increased spectral purity directly translated into a larger information bandwidth of the laser beam and longer possible transmission distances in the optical fiber—with the result that more information could be carried farther and faster than ever before.

    At the time, this unprecedented spectral purity was a direct consequence of the incorporation of a nanoscale corrugation within the multilayered structure of the laser. The washboard-like surface acted as a sort of internal filter, discriminating against spurious “noisy” waves contaminating the ideal wave frequency. Although the old S-DFB laser had a successful 40-year run in optical communications—and was cited as the main reason for Yariv receiving the 2010 National Medal of Science—the spectral purity, or coherence, of the laser no longer satisfies the ever-increasing demand for bandwidth.

    “What became the prime motivator for our project was that the present-day laser designs—even our S-DFB laser—have an internal architecture which is unfavorable for high spectral-purity operation. This is because they allow a large and theoretically unavoidable optical noise to comingle with the coherent laser and thus degrade its spectral purity,” he says.

    The old S-DFB laser consists of continuous crystalline layers of materials called III-V semiconductors—typically gallium arsenide and indium phosphide—that convert into light the applied electrical current flowing through the structure. Once generated, the light is stored within the same material. Since III-V semiconductors are also strong light absorbers—and this absorption leads to a degradation of spectral purity—the researchers sought a different solution for the new laser.

    The high-coherence new laser still converts current to light using the III-V material, but in a fundamental departure from the S-DFB laser, it stores the light in a layer of silicon, which does not absorb light. Spatial patterning of this silicon layer—a variant of the corrugated surface of the S-DFB laser—causes the silicon to act as a light concentrator, pulling the newly generated light away from the light-absorbing III-V material and into the near absorption-free silicon.

    This newly achieved high spectral purity—a 20 times narrower range of frequencies than possible with the S-DFB laser—could be especially important for the future of fiber-optic communications. Originally, laser beams in optic fibers carried information in pulses of light; data signals were impressed on the beam by rapidly turning the laser on and off, and the resulting light pulses were carried through the optic fibers. However, to meet the increasing demand for bandwidth, communications system engineers are now adopting a new method of impressing the data on laser beams that no longer requires this “on-off” technique. This method is called coherent phase communication.

    In coherent phase communications, the data resides in small delays in the arrival time of the waves; the delays—a tiny fraction (10-16) of a second in duration—can then accurately relay the information even over thousands of miles. The digital electronic bits carrying video, data, or other information are converted at the laser into these small delays in the otherwise rock-steady light wave. But the number of possible delays, and thus the data-carrying capacity of the channel, is fundamentally limited by the degree of spectral purity of the laser beam. This purity can never be absolute—a limitation of the laws of physics—but with the new laser, Yariv and his team have tried to come as close to absolute purity as is possible.

    These findings were published in a paper titled, High-coherence semiconductor lasers based on integral high-Q resonators in hybrid Si/III-V platforms. In addition to Yariv, Santis, and Steger, other Caltech coauthors include graduate student Yaakov Vilenchik, and former graduate student Arseny Vasilyev (PhD, ’13). The work was funded by the Army Research Office, the National Science Foundation, and the Defense Advanced Research Projects Agency. The lasers were fabricated at the Kavli Nanoscience Institute at Caltech.

    See the full article here.

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
    Caltech buildings

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  • richardmitnick 9:31 am on December 17, 2013 Permalink | Reply
    Tags: , , Laser Technology, , , ,   

    From Livermore Lab: “Lawrence Livermore researchers demonstrate high-energy betatron X-rays” 

    Lawrence Livermore National Laboratory

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

    A Lawrence Livermore team, along with researchers from the University of California at Los Angeles and SLAC National Accelerator Laboratory, has recently produced some of the highest energy betatron X-rays ever demonstrated, with the added benefit of being produced on a system the size of a large tabletop.

    LLNL researchers Felicie Albert (center) and Bradley Pollock (far right) prepare the Callisto laser system and setup for betatron X-ray experiments at the Laboratory’s Jupiter Laser Facility.


    Betatron X-ray radiation, produced when relativistic electrons are accelerated and oscillate in a laser-driven plasma channel (during a process known as laser-wakefield acceleration), is an X-ray source holding great promise for future high energy density (HED) science experiments. X-rays produced in this manner are femtosecond in duration, directional, spatially coherent and broadband, making them highly attractive as a probe.

    “This source could someday be an alternative to X-ray synchrotrons and free electron lasers. These machines are expensive, complex, and kilometers in length,” said lead author Felicie Albert. “As a result, few of these exist worldwide, and their size prevents their use as mobile systems or as diagnostic tools in conjunction with other large-scale HED drivers, such as the National Ignition Facility.”

    The experiments were performed at LLNL’s Jupiter Laser Facility, using the 200-Terawatt Callisto laser system. By focusing Callisto’s 60 femtosecond laser pulse onto a gas cell filled with helium, the researchers produced up to 80 kiloelectronvolts of betatron X-rays and measured for the first time the angular dependence of betatron X-ray spectra in a laser-wakefield accelerator.

    “We hope to use this remarkable X-ray tool to explore the properties of high energy density plasmas at femtosecond resolution and at the atomic level, which are poorly understood at present,” Albert said. “Many applications beckon on the horizon, as these X-rays could be used in any research involving X-ray synchrotron or free electron laser radiation. It could be used to discover new physical properties of materials at the high pressures and temperatures found only in planet interiors and fusion plasmas.”

    Albert was joined by LLNL’s Bradley Pollock, Joseph Ralph, Yu-Hsin Chen, David Alessi and Arthur Pak and collaborators from the UCLA Department of Electrical Engineering and the SLAC National Accelerator Laboratory. This work, supported by the LLNL Laboratory Directed Research and Development program, was reported in the Dec. 6 issue of Physical Review Letters.

    See the full article here.

    Operated by Lawrence Livermore National Security, LLC, for the Department of Energy’s National Nuclear Security
    DOE Seal

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  • richardmitnick 1:51 pm on September 30, 2013 Permalink | Reply
    Tags: , Laser Technology, ,   

    From SLAC: “Researchers Demonstrate ‘Accelerator on a Chip’” 

    September 27, 2013

    In an advance that could dramatically shrink particle accelerators for science and medicine, researchers used a laser to accelerate electrons at a rate 10 times higher than conventional technology in a nanostructured glass chip smaller than a grain of rice.

    Nanofabricated chips of fused silica just 3 millimeters long were used to accelerate electrons at a rate 10 times higher than conventional particle accelerator technology. (Brad Plummer/SLAC)

    The achievement was reported today in Nature by a team including scientists from the U.S. Department of Energy’s (DOE) SLAC National Accelerator Laboratory and Stanford University.

    “We still have a number of challenges before this technology becomes practical for real-world use, but eventually it would substantially reduce the size and cost of future high-energy particle colliders for exploring the world of fundamental particles and forces,” said Joel England, the SLAC physicist who led the experiments. “It could also help enable compact accelerators and X-ray devices for security scanning, medical therapy and imaging, and research in biology and materials science.”

    Because it employs commercial lasers and low-cost, mass-production techniques, the researchers believe it will set the stage for new generations of “tabletop” accelerators.

    At its full potential, the new “accelerator on a chip” could match the accelerating power of SLAC’s 2-mile-long linear accelerator in just 100 feet, and deliver a million more electron pulses per second.

    See the full article here.

    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

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