DOE News
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    The DOE Science News Source is a Newswise initiative to promote research news from the Office of Science of the DOE to the public and news media.
    • 2017-10-16 12:05:30
    • Article ID: 683028

    Chemical Treatment Improves Quantum Dot Lasers

    Doctored dots release laser light more efficiently, use less power

    • Credit: Los Alamos National Laboratory

      Los Alamos National Laboratory Chemist Jaehoon Lim works on an apparatus that synthesizes quantum dots along with Los Alamos researcher Young-Shin Park (also with the University of New Mexico Center for High-Technology Materials). In a paper published in Nature Nanotechnology, Los Alamos colleagues Kaifeng Wu and Victor Klimov worked with Lim and Park to demonstrate that negatively charged quantum dots show promise for low-power laser applications or quantum dot laser diodes.

    LOS ALAMOS, N.M., Oct. 16, 2017—One of the secrets to making tiny laser devices such as opthalmic surgery scalpels work even more efficiently is the use of tiny semiconductor particles, called quantum dots. In new research at Los Alamos National Laboratory’s Nanotech Team, the ~nanometer-sized dots are being doctored, or “doped,” with additional electrons, a treatment that nudges the dots ever closer to producing the desired laser light with less stimulation and energy loss.

    “When we properly tailor the compositional profile within the particles during their fabrication, and then inject two or more electrons in each dot, they become more able to emit laser light. Importantly, they require considerably less power to initiate the lasing action,” said Victor Klimov, leader of the Nanotech team.

    In order to force a material to emit laser light one has to work toward a “population inversion,” that is, making the number of electrons in a higher-energy electronic state exceed the number that are in a lower-energy state. To achieve this condition normally, one applies an external stimulus (optical or electrical) of a certain power, which should exceed a critical value termed the “optical-gain threshold.” In a recent paradigm-changing advance, Los Alamos researchers demonstrated that by adding extra electrons into their specially designed quantum dots, they can reduce this threshold to virtually zero.

    A standard lasing material, when stimulated by a pump, absorbs light for a time before it starts to lase. On the way to lasing, the material transitions through the state of “optical transparency” when light is neither absorbed nor amplified. By adding extra charge carriers to their quantum dots, the Los Alamos researchers were able to block absorption and create the state of transparency without external stimulation. This implies that even extremely weak pumping can now initiate lasing emission.

    Another important ingredient of this research is a new type of quantum dots with their interiors designed to maintain the lasing-active state for much longer than standard particles do. Normally, the presence of extra electrons would suppress lasing because quantum dot energy is quickly released not as a photon stream but wasteful heat. The new Los Alamos particle design eliminates these parasitic losses, redirecting the particle’s energy into the emission channel.   

    “These studies open exciting opportunities for realizing new types of low-threshold lasing devices that can be fabricated from solution using a variety of substrates and optical cavity designs for applications ranging from fiber optics and large-scale lasing arrays to laser lighting and lab-on-a-chip sensing technologies,” Klimov said.

    The research is described in the journal Nature Nanotechnology this week, authored by project members Kaifeng Wu (a Los Alamos Director’s postdoctoral fellow), Young-Shin Park (guest scientist, University of New Mexico), Jaehoon Lim (Los Alamos postdoctoral research associate) and Victor I. Klimov (Laboratory Fellow, project leader).

    Publication: Kaifeng Wu, Young-Shin Park, Jaehoon Lim, and Victor I. Klimov, “Towards zero-threshold optical gain using charged semiconductor quantum dots,” Nature Nanotechnology.

    Funding: The work on the synthesis of graded quantum dots and studies of Auger recombination in synthesized materials was supported by the DOE Office of Science. The studies of the effect of charging on quantum dot optical gain properties were supported by the Laboratory Directed Research and Development (LDRD) program at Los Alamos National Laboratory.

    About Los Alamos National Laboratory (www.lanl.gov)

    Los Alamos National Laboratory, a multidisciplinary research institution engaged in strategic science on behalf of national security, is operated by Los Alamos National Security, LLC, a team composed of Bechtel National, the University of California, BWX Technologies, Inc. and URS Corporation for the Department of Energy’s National Nuclear Security Administration.

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    X-Rays Show How Periods of Stress Changed an Ice Age Hyena to the Bone

    An international team has unearthed what life might have been like for a now-extinct subspecies of spotted hyena. They found that despite their massive size, some cave hyenas experienced times of hardship that affected them to the bone, causing areas of arrested growth that appear as dark lines, like rings on a tree trunk.

    Turning Wood Scraps into Tape

    A new chemical process converts a component of wasted wood pulp and other biomass into high-value pressure-sensitive adhesives.

    Very Heavy Elements Deliver More Electrons

    Scientists revise understanding of the limits of bonding for very electron-rich heavy elements.

    Detecting Light in a Different Dimension

    UPTON, NY--Scientists from the Center for Functional Nanomaterials (CFN)--a U.S. Department of Energy (DOE) Office of Science User Facility at Brookhaven National Laboratory--have dramatically improved the response of graphene to light through self-assembling wire-like nanostructures that conduct electricity.

    From the Cosmos to Fusion Plasmas, PPPL Presents Findings at Global APS Gathering

    Invited Princeton Plasma Physics Laboratory talks at 60th American Physical Society-Department of Plasma Physics annual meeting.

    Scientists Bring Polymers Into Atomic-Scale Focus

    A Berkeley Lab-led research has adapted a powerful electron-based imaging technique to obtain a first-of-its-kind image of atomic-scale structure in a synthetic polymer. The research could ultimately inform polymer fabrication methods and lead to new designs for materials and devices that incorporate polymers.

    Probing Water's "No-Man's Land" Temperature Region

    Measuring the physical properties of water at previously unexplored temperatures offers insights into one of the world's essential liquids.

    Novel Soil Bacteria with Unusual Genes Synthesize Unique Antibiotic Precursors

    A large-scale soil project uncovered genetic information from bacteria with the capacity to make specialized molecules that could lead to new pharmaceuticals.

    RTI International to Perform Large-Scale Tests of Its Innovative Carbon Capture Technology for Cleaner, Less Costly Power

    RTI International announced today its participation in a 2-1/2 year collaborative project to advance its non-aqueous solvent (NAS)-based CO2 capture technology for post-combustion CO2 capture at coal-fired power plants

    Unlocking the Secrets of Metal-Insulator Transitions

    Using an x-ray technique available at the National Synchrotron Light Source II (NSLS-II), scientists found that the metal-insulator transition in the correlated material magnetite is a two-step process. The researchers from the University of California Davis published their paper in the journal Physical Review Letters.


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    DOE funding advances project to turn captured CO2 into key chemicals

    The U.S. Department of Energy has selected Southern Research for an award of up to $1.5 million to advance technology for carbon dioxide utilization.

    Sierra Reaches Higher Altitudes, Takes Number Two Spot on List of Fastest Supercomputers

    Sierra, Lawrence Livermore National Laboratory's newest supercomputer, rose to second place on the list of the world's fastest computing systems, TOP500 List representatives announced Monday at the International Conference for High Performance Computing, Networking, Storage and Analysis conference (SC18) in Dallas.

    Green energy: Wind energy agreement will provide savings, 50 percent of electricity needs for Kansas State University Manhattan campus

    Kansas State University has signed an agreement with Westar Energy to provide approximately 50 percent of the energy needs for the university's main Manhattan campus from a wind farm in Nemaha County and save the university nearly $200,000 annually.

    INCITE grants awarded to 62 computational research projects

    The U.S. Department of Energy announced new projects for 2019 through its Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program.

    Argonne's Raj Kettimuthu Named ACM Distinguished Member

    Argonne computer scientist Raj Kettimuthu recently was named a Distinguished Member of the Association for Computing Machinery for his development of tools to analyze and enhance end-to-end data transfer performance.

    Jefferson Lab-Affiliated Researchers Honored as APS Fellows

    The Department of Energy's Thomas Jefferson National Accelerator Facility now has a few more fellows on campus. The American Physical Society, a professional membership society that works on behalf of the physics community, recently announced its list of 2018 fellowships.

    Jefferson Lab Receives DOE Award for Energy Efficient Upgrade

    On Oct. 23, a team from the Department of Energy's Thomas Jefferson National Accelerator Facility was honored at the 2018 Federal Energy and Water Management Award Ceremony for upgrades made to the lab's data center, ultimately improving its energy efficiency.

    Free Science Events and Educational Opportunities Expected to Draw Thousands

    The Plasma Sciences Expo--planned as the biggest celebration of plasma physics in the country--presents teachers, students and the public with a free opportunity to explore what scientists call "the fourth state of matter."

    Triad National Security Takes the Helm at Los Alamos National Laboratory

    LOS ALAMOS, N.M., November 1, 2018 -- Los Alamos National Laboratory begins operations today under a new management and operating (M&O) contract between Triad National Security, LLC (Triad) and the U.S. Department of Energy's National Nuclear Security Administration (NNSA). The NNSA awarded the M&O contract to Triad on June 8, 2018.

    Texas McCombs Master of Science Programs in Finance, Marketing and Energy Receive STEM Certification

    Several programs within the McCombs School of Business have received STEM designation.


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    Turning Wood Scraps into Tape

    A new chemical process converts a component of wasted wood pulp and other biomass into high-value pressure-sensitive adhesives.

    Very Heavy Elements Deliver More Electrons

    Scientists revise understanding of the limits of bonding for very electron-rich heavy elements.

    Probing Water's "No-Man's Land" Temperature Region

    Measuring the physical properties of water at previously unexplored temperatures offers insights into one of the world's essential liquids.

    Novel Soil Bacteria with Unusual Genes Synthesize Unique Antibiotic Precursors

    A large-scale soil project uncovered genetic information from bacteria with the capacity to make specialized molecules that could lead to new pharmaceuticals.

    Warmer Temperatures Lengthen Growing Season, Increase Plants' Vulnerability to Frost

    Experimental warming treatments show how peatland forests may respond to future environmental change.

    Rising Stars Seek to Learn from the Master: Mother Nature

    A trio of scientists was recognized for their early career successes in uncovering how microbes produce fuel, insights that could change our energy portfolio

    How Plant Cells Decide When to Make Oil

    Signaling mechanism details discovered, potentially leading to strategies to engineer plants that make more bio-oil.

    Cryocooler Cools an Accelerator Cavity

    Researchers demonstrated cryogen-free operation of a superconducting radio-frequency cavity that might ease barriers to its use in societal applications.

    Shining Light on the Separation of Rare Earth Metals

    New studies identify key molecular characteristics to potentially separate rare earth metals cleanly and efficiently with light.

    Placing Atoms for Optimum Catalysts

    Precise positioning of oxygens could help engineer faster, more efficient energy-relevant chemical transformations.


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