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  • richardmitnick 12:24 pm on October 21, 2021 Permalink | Reply
    Tags: "Need for Larger Space Telescope Inspires Lightweight Flexible Holographic Lens", , , Optics and Photonics, , , The holographic optical element is a refined version of a Fresnel lens., The new method allows the designers to either focus light onto a single point or disperse it into its constituent colors.   

    From Rensselaer Polytechnic Institute (US) : “Need for Larger Space Telescope Inspires Lightweight Flexible Holographic Lens” 

    From Rensselaer Polytechnic Institute (US)

    October 21, 2021
    Mary L. Martialay

    1
    New technique produces lens for focused image or spectrum.

    Inspired by a concept for discovering exoplanets with a giant space telescope, a team of researchers is developing holographic lenses that render visible and infrared starlight into either a focused image or a spectrum. The experimental method, detailed in an article appearing today in Nature Scientific Reports, could be used to create a lightweight flexible lens, many meters in diameter, that could be rolled for launch and unfurled in space.

    “We use two spherical waves of light to produce the hologram, which gives us fine control over the diffractive grating recorded on the film, and the effect it has on light — either separating light with super sensitivity, or focusing light with high resolution,” said Mei-Li Hsieh, a visiting researcher at Rensselaer Polytechnic Institute and an expert in optics and photonics who established a mathematical solution to govern the output of the hologram. “We believe this model could be useful in applications that require extremely high spectral resolution spectroscopy, such as analysis of exoplanets.”

    Hsieh, who also holds a faculty position at National Yang Ming Chiao Tung University[國立陽明交通大學](TW) in Taiwain, along with Rensselaer physicists Shawn-Yu Lin and Heidi Jo Newberg, worked with Thomas D. Ditto, an artist and inventor who conceived the idea of an optical space telescope freed of conventional, and heavy, glass mirrors and lenses. Ditto first worked at Rensselaer in the 1970s and is currently a visiting researcher in astrophysics.

    Telescopes that must be launched into space (to benefit from a view unimpeded by Earth’s atmosphere) are limited by the weight and bulk of glass mirrors used to focus light, which can realistically span only a few meters in diameter. By contrast, the lightweight flexible holographic lens — more properly called a “holographic optical element” — used to focus light could be dozens of meters across. Such an instrument could be used to directly observe an exoplanet, a leap over current methods that detect exoplanets based on their effect on light coming from the star they orbit, said Newberg, a Rensselaer professor of physics, applied physics, and astronomy.

    “To find Earth 2.0, we really want to see exoplanets by direct imaging — we need to be able to look at the star and see the planet separate from the star. And for that, we need high resolution and a really big telescope,” said Newberg, an astrophysicist and expert in galactic structure.

    The holographic optical element is a refined version of a Fresnel lens, a category of lenses that use concentric rings of prisms arrayed in a flat plane to mimic the focusing ability of a curved lens without the bulk. The concept of the Fresnel lens — which was developed for use in lighthouses —dates to the 19th century, with modern-day Fresnel lenses of glass or plastic found in automobile lamps, micro-optics, and camera screens.

    But while Fresnel holographic optical elements — created by exposing a light-sensitive plastic film to two sources of light at different distances from the film — are not uncommon, existing methods were limited to lenses that could only focus light, rather than separating it into its constituent colors.

    The new method allows the designers to either focus light onto a single point or disperse it into its constituent colors, producing a spectrum of pure colors, said Lin, corresponding author and a Rensselaer professor of physics, applied physics, and astronomy. The method uses two sources of light, positioned very close to one another, which create concentric waves of light that — as they travel toward the film — either build or cancel each other out. This pattern of convergence or interference can be tuned based on the formulas Hsieh developed. It is printed, or “recorded,” onto the film as a holographic image and, depending on how the image is structured, light passing through the holographic optical element is either focused or stretched.

    “We wanted to stretch the light, so that we could separate it into different wavelengths. Any Fresnel lens will stretch the light a little, but not enough,” said Lin, an expert in photonic crystals and nano-photonics. “With our method, we can have super resolution on one end, or super sensitive — with each color separated. When the light is stretched like that, the color is very good, as pure and as vivid as you can get.”

    Hsieh, Newberg, Lin, and Ditto were joined in the research by Yi-Wen Lee and Shiuan-Huei Lin of National Yang Ming Chiao Tung University.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Founded in 1824, Rensselaer Polytechnic Institute (US) is America’s first technological research university. Rensselaer encompasses five schools, 32 research centers, more than 145 academic programs, and a dynamic community made up of more than 7,900 students and more than 100,000 living alumni. Rensselaer faculty and alumni include more than 145 National Academy members, six members of the National Inventors Hall of Fame, six National Medal of Technology winners, five National Medal of Science winners, and a Nobel Prize winner in Physics. With nearly 200 years of experience advancing scientific and technological knowledge, Rensselaer remains focused on addressing global challenges with a spirit of ingenuity and collaboration.

    With 7,900 students and more than 100,000 living alumni, Rensselaer is addressing the global challenges facing the 21st century—to change lives, to advance society, and to change the world.

    RPI is organized into six main schools which contain 37 departments, with emphasis on science and technology It is recognized for its degree programs in engineering, computing, business and management, information technology, the sciences, design, and liberal arts. As of 2017, RPI’s faculty and alumni include six members of the National Inventors Hall of Fame (US), six National Medal of Technology winners, five National Medal of Science winners, eight Fulbright Scholarship recipients, and a Nobel Prize winner in Physics; in addition, 86 faculty or alumni are members of the National Academy of Engineering (US), 17 of the National Academy of Sciences (US), 25 of the American Academy of Arts and Sciences (US), eight of the National Academy of Medicine (US), one of the National Academy of Public Administration (US), and nine of the National Academy of Inventors (US).

    From renewable energy to cybersecurity, from biotechnology to materials science, from big data to nanotechnology, the world needs problem solvers—exactly the kind of talent Rensselaer produces—to address the urgent issues of today and the emerging issues of tomorrow.

    Research and development

    Rensselaer is classified among “R1: Doctoral Universities – Very High Research Activity”. Rensselaer has established six areas of research as institute priorities: biotechnology, energy and the environment, nanotechnology, computation and information technology, and media and the arts. Research is organized under the Office of the Vice President for Research. In 2018, Rensselaer operated 34 research centers and maintained annual sponsored research expenditures of $100.8 million.
    Center for Biotechnology and Interdisciplinary Studies

    One of the most recent of Rensselaer’s research centers is the Center for Biotechnology and Interdisciplinary Studies, a 218,000 square-foot research facility and a national pacesetter for fundamental and applied research in biotechnology. The primary target of the research center is biologics, a research priority based on data-driven understanding of proteomics, protein regulation, and gene regulation. It involves using biocatalysis and synthetic biology tools to block or supplement the actions of specific cells or proteins in the immune system. Over the past decade, CBIS has produced over 2,000 peer-reviewed publications with over 30,000 citations and currently employs over 200 scientists and engineers. The center is also used primarily to train undergraduate and graduate students, with over 1,000 undergraduates and 200 doctoral students trained.

    The center also has numerous academic and industry partners including the Icahn School of Medicine at Mount Sinai. These partnerships have resulted in numerous advances over the last decade through new commercial developments in diagnostics, therapeutics, medical devices, and regenerative medicine which are a direct result of research at the center. Examples of advancements include the creation of synthetic heparin, antimicrobial coatings, detoxification chemotherapy, on-demand bio-medicine, implantable sensors, and 3D cellular array chips.

    Rensselaer also hosts the Tetherless World Constellation (US), a multidisciplinary research institution focused on theories, methods, and applications of the World Wide Web. Research is carried out in three inter-connected themes: Future Web, Semantic Foundations and Xinformatics. At Rensselaer, a constellation is a multidisciplinary team composed of senior and junior faculty members, research scientists, and postdoctoral, graduate, and undergraduate students. Faculty alumni of TWC includes Heng Ji (Natural Language Processing). In 2016, the Constellation received a one million dollar grant from the Bill & Melinda Gates Foundation (US) for continuing work on a novel data visualization platform that will harness and accelerate the analysis of vast amounts of data for the foundation’s Healthy Birth, Growth, and Development Knowledge Integration initiative.

    In conjunction with the constellation, Rensselaer operates the Center for Computational Innovations which is the result of a $100 million collaboration between Rensselaer, IBM, and New York State to further nanotechnology innovations. The center’s main focus is on reducing the cost associated with the development of nanoscale materials and devices, such as used in the semiconductor industry. The university also utilizes the center for interdisciplinary research in biotechnology, medicine, energy, and other fields. Rensselaer additionally operates a nuclear reactor and testing facility – the only university-run reactor in New York State – as well as the Gaerttner Linear Accelerator, which is currently being upgraded under a $9.44 million grant from the Department of Energy (US).

     
  • richardmitnick 11:08 am on November 20, 2019 Permalink | Reply
    Tags: "Gas Terahertz Laser is No Laughing Matter", Exploiting vibrational states, , Optics and Photonics, QCL-quantum cascade laser, Terahertz: Applications and limitations, The latest work uses a QCL as a pump rather than as the lasing medium itself., THz waves could be used for wireless communication., Using nitrous oxide the researchers showed that the gas lased.   

    From Optics & Photonics: “Gas Terahertz Laser is No Laughing Matter” 

    From Optics & Photonics

    18 November 2019
    Edwin Cartlidge

    1
    A laser the size of a shoebox produces THz waves (in green) by using a quantum cascade laser (red) to excite and rotate nitrous oxide molecules packed inside a 15cm-long cavity. [Image: Chad Scales, U.S. Army Futures Command]

    Scientists in the U.S. have dusted off and updated plans for a gas laser that can generate beams in the elusive terahertz (THz) frequency band. By pumping nitrous oxide (laughing gas) with a quantum cascade laser, they have shown it is possible to produce a broad spectrum of THz radiation using a compact device operating at room temperature [Science]

    Among the applications of such radiation, they say, are sensing, imaging and communication.

    Terahertz: Applications and limitations

    THz radiation sits in the electromagnetic spectrum between microwaves at lower frequencies and infrared waves above. The fact that it passes through many common materials, such as clothing, plastic and paper, while not having the energy to ionize and therefore harm living tissue, means it is potentially well-suited as a scanning technology. At the same time, its absorption by certain substances at well-defined frequencies suggests its use as a sensor of atmospheric gases.

    In addition, THz waves could be used for wireless communication. Not only could they accommodate higher bandwidths than lower-frequency radio waves, their relatively short range could also be exploited to prevent eavesdropping—with the amount of atmospheric absorption depending on the precise frequency used.

    Unfortunately, however, building suitable THz sources has proved difficult. There are a number of different technologies on the market—such as those that multiply harmonics of microwaves or mix the output of lasers—but each has its own limitations. None has a significant output around 1 THz, while many are bulky and expensive.

    In recent years, researchers have started to make THz sources from quantum cascade lasers (QCLs), whose alternating layers of high- and low-bandgap semiconductor create quantum wells that force electrons to emit a series of photons at specific wavelengths. Such lasers are chip-based, making them potentially small and cheap, but they need to be cooled, are inefficient and cover a limited frequency range.

    Exploiting vibrational states

    In contrast, the latest work uses a QCL as a pump, rather than as the lasing medium itself. The laser in this case consists of a gas of nitrous oxide, the molecules of which when pumped vibrate and then move into specific rotational states. Held in a suitable cavity, the molecules emit THz photons in the form of a laser beam when dropping back down from one rotational state to another.

    In previous decades, cavities several meters long were pumped by large carbon-dioxide lasers. Theoretical models predicted that if the cavity were too small, and the pressure of the gas too high, collisions between gas molecules would prevent the build-up of energy necessary for a population inversion.

    Henry Everitt of Duke University, NC, developed a model in the 1980s showing it should in fact be possible to build such compact molecular lasers. However, that model still involved a carbon-dioxide laser as the pump. It was only after working on the theory for a number of years, in collaboration with Steven Johnson and colleagues at the Massachusetts Institute of Technology, MA, he says, did it become clear that a QCL could also pack enough power to make the gas lase.

    The trick, according to Johnson, lay in considering vibrational states of the molecules that had been previously overlooked. By limiting energy dissipation when pressure in the cavity is high, he explains in a press release accompanying the research, those vibrations “sort of give you more breathing room to keep rotating and keep making THz waves.”

    Lasing with laughing gas

    Exploiting that insight, Everitt, who now works for the U.S. Army, teamed up with Federico Capasso and colleagues at Harvard University, MA. Capasso co-invented QCLs while at Bell Labs in the 1990s, and his group has now used an infrared QCL to pump a gas-filled copper tube just 15 centimeters long and 5 millimeters in diameter.

    Using nitrous oxide, the researchers showed that the gas lased. What’s more, they found that the frequency of that laser beam varied as they tuned the QCL. They were able to produce 37 lines, each with a width of just a few kilohertz, across the spectrum from 0.25 to 0.96 THz. They also used modeling to show that many other gases pumped in this way—each being paired to its own QCL—should produce laser lines spanning more than 1 THz.

    According to Capasso, the device outperforms all existing laser sources in this region of the spectrum—something, he adds, that could not have been predicted with any confidence when he and his colleagues embarked on the research. “It was not obvious that pumping with a broadly tunable mid-infrared QCL was the way to get broadband THz lasing in a gas,” he says.

    But Capasso notes that there are still hurdles to overcome before the technology can be commercialized and made ready for real-world applications. Among these, he says, are optimizing the cavity to boost power output as well as changing the gas to carbon monoxide in order to expand the laser’s range up a few THz.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Opticsand Photonics News (OPN) is The Optical Society’s monthly news magazine. It provides in-depth coverage of recent developments in the field of optics and offers busy professionals the tools they need to succeed in the optics industry, as well as informative pieces on a variety of topics such as science and society, education, technology and business. OPN strives to make the various facets of this diverse field accessible to researchers, engineers, businesspeople and students. Contributors include scientists and journalists who specialize in the field of optics. We welcome your submissions.

     
  • richardmitnick 2:26 pm on November 10, 2018 Permalink | Reply
    Tags: A topological-insulator laser confronting a material defect simply detours around it and then happily continues on its way around the device perimeter, Emerging discipline of topological photonics, One of the attractions of photons as qubit candidates is that they are largely immune to the thermal and electromagnetic noise that can bedevil other quantum systems, Optics and Photonics,   

    From Optics & Photonics: “A Topological Shield for Entangled Photons” 

    From Optics & Photonics

    08 November 2018
    Stewart Wills

    Some researchers in quantum computing look to pairs or ensembles of entangled photons as the best candidates for information-carrying quantum bits (qubits). But entangled photonic quantum states are skittish things, prone to evaporate in imperfect, real-world devices built to meaningful scale. How can the quantum information in photonic qubits be protected long enough to do useful work in a real quantum computer?

    1
    Andrea Blanco-Redondo of the University of Sydney Nano Institute led research exploring topological protection for correlated biphoton states, which could clear one hurdle for photons as quantum information carriers. [Image: Jayne Ion/University of Sydney]

    One answer could lie in the emerging discipline of topological photonics. A group of researchers in Australia and Israel, led by OSA member Andrea Blanco-Redondo of the University of Sydney Nano Institute, has now experimentally demonstrated a platform for extending “topological protection” to delicate correlated biphoton states—and shown how the platform might be used to build robust logic gates for quantum computing (Science).

    Sensitive to imperfections

    One of the attractions of photons as qubit candidates is that they are largely immune to the thermal and electromagnetic noise that can bedevil other quantum systems, such as trapped-ion and superconductor platforms. But photonic qubits have their own vulnerabilities. Notably, they’re prone to potential losses and other errors due to scattering as the photons run up against fabrication imperfections.

    Thus, while photons have excelled in the lab in proof-of-principle demonstrations of entanglement, it’s been hard to envision how they might be made to work in a practical quantum device, where at least some fabrication defects are unavoidable. Increasingly, however, the physics of topology—which captured the 2016 Nobel Prize for its pioneers in condensed-matter physics—has seemed to hold one key to solving this photonic-qubit quandary.

    Protection in topology

    2
    One recent example of a topological photonic system, published in February 2018, was a topological-insulator laser demonstrated by a team at The Technion and CREOL. [Image: S. Wittek (CREOL) and M.A. Bandres (Technion)]

    Topological systems involve materials that, by virtue of the details of their underlying symmetry, possess unusual physical characteristics, best exemplified by so-called topological edge states. In the realm of photonics, these edge states have been leveraged to create exotic proof-of-principle quantum devices such as chips that steer single photons around corners, and lasers that send light in one direction around the edges of an array of microresonators.

    Another key feature stoking interest in “topologically nontrivial” photonic systems is that they are “robust to disorder.” For example, a topological-insulator laser confronting a material defect simply detours around it, and then happily continues on its way around the device perimeter.

    That has raised the prospect that this shroud of topological protection could be thrown around single and entangled photons in quantum computers and devices, to keep them safe from losing information to scattering and fabrication imperfections. But experiments thus far in topological protection of photons have generally involved only single photons—not the entangled photon pairs or ensembles required for quantum information systems.

    Silicon nanowire array

    To extend topological protection to a multiphoton quantum state, Blanco-Redondo’s team—which also included Bryn Bell and OSA Fellow Ben Eggleton at the University of Sydney, and Dikla Oren and OSA Fellow Mordechai Segev at The Technion, Israel—began with a platform that, in previous work [Physical Review Letters], they had shown could produce a topological edge state.

    The platform consists of a 1-D array of silicon nanowires with alternating short and long gaps, which creates a structure known as a Su-Schrieffer-Heeger (SSH) lattice. By introducing a “long-long” defect in the middle of the lattice, the team coaxed the structure into displaying topological edge-state behavior and topological protection at the interface between the two-sides of the lattice.

    3
    The team’s experimental setup involves a lattice of silicon nanowires with a central defect, which creates an “edge state” that provides topological protection for paired photons traveling down the central waveguide. [Image: Rhys Holland & Sebastian Zentilomo/University of Sydney]

    The researchers next pumped light from a picosecond 1550-nm pulsed laser into the waveguide at the center of the lattice. The pump pulses generated correlated signal and idler photons via a spontaneous four-wave mixing (SFWM) process; those photons were filtered, collected in superconducting single-photon detectors, and analyzed at the end of the line to establish correlation between the photons’ quantum states.

    Testing for topological protection

    4
    Artists’ rendering of correlated photons in the nanowire lattice. [Image: Sebastian Zentilomo/University of Sydney]

    Finally, with the presence of correlated biphotons established, the team got down to testing whether the system could provide topological protection for the quantum states of those photon pairs. To do so, the researchers introduced random disorders into the SSH lattice and tested whether the quantum states of the biphotons were preserved.

    They found that the correlation and quantum state of the biphotons—which would have been scattered and lost across a uniform, topologically trivial lattice—held up well even amid fairly high levels of lattice disorder in the SSH system. The researchers also demonstrated experimentally how several of these lattices, put together, could form “a key building block” to construct entangled quantum systems with topological protection. And they showed how such entangled systems might be used to create a simple two-qubit logic gate for quantum computing.

    Toward photonic quantum gates

    Blanco-Redondo, in a press release [no link provided] accompanying the work, suggested that the study results offer “a pathway to build robust entangled states for logic gates using protected pairs of photons.” The team is now working on improving the platform, toward the goal of building such quantum gates. The effort, if successful, could provide a boost to the prospects for photons as quantum information carriers in real-world applications.

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Optics & Photonics News (OPN) is The Optical Society’s monthly news magazine. It provides in-depth coverage of recent developments in the field of optics and offers busy professionals the tools they need to succeed in the optics industry, as well as informative pieces on a variety of topics such as science and society, education, technology and business. OPN strives to make the various facets of this diverse field accessible to researchers, engineers, businesspeople and students. Contributors include scientists and journalists who specialize in the field of optics. We welcome your submissions.

     
  • richardmitnick 12:26 am on August 29, 2018 Permalink | Reply
    Tags: A Programmable Quantum Chip, Optics and Photonics, Packs in more than 200 separate photonic components, , , Two-qubit quantum processor, , via Silicon Photonics   

    From U Bristol via Optics & Photonics: “A Programmable Quantum Chip, via Silicon Photonics” 

    From University of Bristol

    via

    From Optics & Photonics

    28 August 2018
    Stewart Wills

    1
    [Image: Xiaogang Qiang/University of Bristol]

    A team led by researchers at the University of Bristol, U.K., has demonstrated a silicon-photonics-based chip that reportedly implements a fully programmable, two-qubit quantum processor [Nature Photonics]. The researchers were able to use the chip, which packs in more than 200 separate photonic components, to program and run 98 different two-qubit operations, as well as an optimization algorithm and a quantum simulation.

    The system—which relies on a different model of quantum information processing (QIP) than the conventional “quantum circuit” model—isn’t ready to scale to a full-fledged universal quantum computer. But the Bristol-led group suggests that its proof-of-concept device concretely demonstrates the potential of silicon as a platform for “full-scale universal quantum technologies using light.”

    Problematic entanglements

    From one perspective, silicon photonics seems the ideal QIP vehicle. It’s compatible with long-standing CMOS manufacturing processes honed in the classical computing business, for example, and features an increasing array of compact, reconfigurable optical components on which to draw for quantum operations. One challenge, though, lies in combining all of the elements necessary for QIP—generating photons, encoding quantum information on them, manipulating them and reading out their quantum state—on a single, programmable device.

    Even more fundamental than these engineering challenges is the issue of using photons for operations that include quantum entanglement, a fundamental requirement for QIP. That’s because, in the conventional circuit model of quantum computing, each arbitrary two-qubit operation requires the equivalent of three consecutive entangling logic gates for control of the quantum system. That’s something that’s been too complex to implement practically using free-space optics or combinations of free-space and integrated photonic systems.

    Changing the model

    The research team, which included not only Bristol scientists but researchers in China and Australia, attacked the problem by focusing on a different QIP model. Rather than one that implements quantum processing as a multiplication of quantum logic gates in series, as under the conventional circuit model, the group used a “linear combination of quantum operators” scheme.

    In this approach, an arbitrary two-qubit unitary operation is reframed as a linear combination, or weighted sum, of four easier-to-implement unitaries. Previous work at Bristol and elsewhere had suggested that the linear-combination approach could simplify control of quantum operations in a programmable QIP framework [Nature Communications]. Even under that ostensibly simpler model, however, putting arbitrarily programmable QIP into practice calls for a formidably complex array of optical components. To achieve the required complexity, the research team turned to silicon photonics, and set their sights on a single photonic chip that could handle the quantum functions end to end.

    The monolithically integrated, silicon-based device that the researchers fabricated to do the job includes four spontaneous four-wave-mixing photon-pair sources, four pump rejection filters, 58 thermo-optical phase shifters, 82 multimode interferometer beamsplitters, 18 waveguide crossers and 40 optical-grating couplers. All of these elements are crowded onto a device with an effective footprint of less than 14 mm^2.

    Nearly 100,000 reprogrammed settings

    This small platform packs in sufficient complexity, according to the researchers, to allow them to perform end-to-end reprogrammable two-qubit operations—generating two photons; turning the photons into qubits by encoding quantum information on them; performing arbitrary unitary operations on those qubits, including entanglement; and reading out the resulting quantum state via quantum tomography. (The light source for the experiments was an externally connected, tunable laser, tied to the chip via a fiber array.)

    The Bristol-led team found that it could program the device to implement 98 different unitary quantum operations, with an average quantum process fidelity of 93.2 ± 4.5 percent. The researchers also programmed the chip to realize a previously developed quantum optimization algorithm, and to simulate a specific kind of “quantum walk,” the quantum analogue to a classical mathematical random walk. Together, the experiments involved some 98,480 different reprogrammed settings.

    Taking on larger tasks

    The team is careful to stress that the chip—or, more precisely, the linear-combination protocol it’s based on—can’t, in its present form, scale to universal quantum computing. That’s because the protocol’s probability of success is inversely proportional to the number of terms, so that “it would achieve exponentially small success probability for a universal quantum computer.” Still, the researchers believe that, through certain optimization and scaling efforts, the platform could expand to handle families of large-scale QIP tasks “with considerable success probability.”

    The researchers also see the system as an important step toward proving the mettle of silicon photonics in the drive for a universal quantum computer. “What we’ve demonstrated is a programmable machine that can do lots of different tasks,” the paper’s lead author, Xiaogang Qiang—previously a University of Bristol Ph.D. student, and now a researcher at the National University of Defence Technology, China—said in a press release accompanying the work.

    “It’s a very primitive processor, because it only works on two qubits, which means there is still a long way before we can do useful computations with this technology,” Qiang continued. “But what is exciting is that it the different properties of silicon photonics that can be used for making a quantum computer have been combined together in one device. This is just too complicated to physically implement with light using previous approaches.”

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Optics & Photonics News (OPN) is The Optical Society’s monthly news magazine. It provides in-depth coverage of recent developments in the field of optics and offers busy professionals the tools they need to succeed in the optics industry, as well as informative pieces on a variety of topics such as science and society, education, technology and business. OPN strives to make the various facets of this diverse field accessible to researchers, engineers, businesspeople and students. Contributors include scientists and journalists who specialize in the field of optics. We welcome your submissions.

    Bristol is one of the most popular and successful universities in the UK and was ranked within the top 50 universities in the world in the QS World University Rankings 2018.

    The University of Bristol is at the cutting edge of global research. We have made innovations in areas ranging from cot death prevention to nanotechnology.

    The University has had a reputation for innovation since its founding in 1876. Our research tackles some of the world’s most pressing issues in areas as diverse as infection and immunity, human rights, climate change, and cryptography and information security.

    The University currently has 40 Fellows of the Royal Society and 15 of the British Academy – a remarkable achievement for a relatively small institution.

    We aim to bring together the best minds in individual fields, and encourage researchers from different disciplines and institutions to work together to find lasting solutions to society’s pressing problems.

    We are involved in numerous international research collaborations and integrate practical experience in our curriculum, so that students work on real-life projects in partnership with business, government and community sectors.

     
  • richardmitnick 3:39 pm on March 22, 2018 Permalink | Reply
    Tags: Laser Fusion at the Microscale, , Optics and Photonics,   

    From Optics & Photonics: “Laser Fusion at the Microscale” 

    Optics & Photonics

    1
    Scanning electron micrograph (a) of deuterated-polyethylene nanowires used in experiments, and numerical simulations (b-d) of those nanowires exploding under the influence of ultra-intense laser pulse. [Image: Advanced Beam Laboratory/CSU]

    3.21.18
    Stewart Wills

    The words “laser fusion” conjure up vast, megajoule laser installations housed in football-field-sized buildings, such as the U.S. National Ignition Facility (see Laser fusion: The uncertain road to ignition, OPN, September 2014). But researchers from the United States and Germany, led by OSA Fellow Jorge Rocca of Colorado State University, recently managed to churn out micro-scale fusion reactions using much more modest equipment. Their setup: a 1-J, tabletop femtosecond laser built from scratch—with a dense array of polyethylene nanowires serving as the fusion target (see Nat. Commun., https://www.nature.com/articles/s41467-018-03445-z).

    The team believes that its recipe could offer a good source of pulses of bright, near-monoenergetic neutrons for some imaging and materials-science applications. And the ability to create extreme plasmas with a compact laser, the researchers suggest, could open interesting windows into high-energy-density science.

    Nanowire forest

    The research team (including scientists from Colorado State University and the Nevada National Security Site, USA, and the Institut für Theoretische Physik, Germany) began its setup by creating 12.5-mm diameter arrays of vertical, 200-nm- and 400-nm-diameter and 5-micron-long nanowires as fusion targets. The wires were made of deuterated polyethylene (CD2), a polymer in which deuterium (so-called heavy hydrogen), with a nucleus including one proton and one neutron, substitutes for ordinary hydrogen, which includes one proton only.

    The researchers arrayed the vertical nanowires on a 200-micron-thick substrate of solid CD2, packing in the wires with sufficient interstitial space to make the array’s density 16 to 19 percent of the density of the solid polymer. That created a “near-solid-density” medium to serve as the target.

    Next, the scientists used a frequency-doubled, 400-nm chirped-pulse amplification Ti:sapphire laser to generate 60-fs laser pulses with total energies of around 1.65 J, and aimed that stream of pulses at the nanowire-forest samples. They focused the pulses into a spot 2 to 2.6 microns in diameter, thereby creating intensities on the order of 1020 W/cm^2 on the target.

    From plasma to fusion

    According to the researchers, the vacant spaces around the nanowires let the energy from the relativistic-intensity laser pulses penetrate deep inside the nanowire structure, where it becomes trapped and “practically totally absorbed.” The absorbed energy rips electrons off of the nanowire surface and accelerates them to high velocities, at which they interact with the nanowires and cause them to explode into a void-filling plasma. Within that plasma, the electron-stripped deuterium nuclei, or deuterons, achieve kinetic energies on the order of 3 MeV. Those energies drive deuteron-deuteron fusion reactions that create streams of neutrons, with a characteristic energy of 2.45 MeV, as by-products.

    In experiments with the nanowire targets, the team found that it could produce fluxes of 2.45-MeV, fusion-generated neutrons some 500 times larger than experiments using flat, solid CD2 targets. The team claims that the observed 2 × 106 neutrons per joule is “the largest D–D fusion neutron yield reported to date for plasmas generated by laser pulse energies in the 1 J range.” And numerical simulations suggest that relatively small increases in laser pulse energy could significantly increase the fusion neutron yield.

    The repetition-rate advantage

    A particular strength of the setup, according to the researchers, is the compact laser’s ability to pump out femtosecond pulses at a high repetition rate, compared with the Hz-scale or slower rates of petawatt-class lasers. The creation of a target that can achieve fusion with these lower-energy, high-repetition-rate lasers, the researchers suggest, is “of significant interest” for high-energy-density science, such as studies of conditions in the cores of stars.

    On a more applied note, the team suggests that its approach using nanowire arrays could allow the creation of efficient point sources of quasi-monoenergetic neutrons for neutron imaging and tomography, neutron diffraction studies in materials science, and other uses.

    See the full article here .

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  • richardmitnick 10:56 am on January 8, 2018 Permalink | Reply
    Tags: Boosting Communications with Magnetic Radio, Low-frequency “magnetic radio” to enable better wireless communications underground underwater and in other environments that are challenging for conventional RF communications, , OPM-optically pumped magnetometer, Optics and Photonics   

    From Optics & Photonics: “Boosting Communications with Magnetic Radio” 

    Optics & Photonics

    07 January 2018
    Stewart Wills

    1
    Dave Howe of the U.S. National Institutes of Standards and Technology (NIST) leads an effort to use optically pumped magnetometers (OPMs) as receivers for low-frequency “magnetic radio,” to enable better wireless communications underground, underwater and in other environments that are challenging for conventional RF communications. [Image: Burrus/NIST]

    Researchers at the U.S. National Institute of Standards (NIST) are working on ways to overcome a vexing problem of a wireless world: how to get usable signals in crowded built environments, underground and even underwater (Rev. Sci. Instr., doi: 10.1063/1.5003821).

    At the heart of the team’s approach is an optically pumped magnetometer (OPM)—a highly sensitive, room-temperature quantum detector that can do double duty as a kind of magnetic-radio receiver. In the NIST setup, the OPM is used to pull in modulated signals encoded in very low frequency (VLF) magnetic fields, which are less prone to attenuation by the surrounding environment than a typical cell or GPS signal. And the team has coupled that sensitive detection technology with a modulation scheme that can pack more information into the otherwise limited bandwidth of VLF fields.

    The skin-depth conundrum

    Anyone who’s struggled to get a decent cell signal in a building basement knows the penetration limits of the high-frequency RF bands used by mobile phones. But the problem goes much further than simple inconvenience. For example, high-frequency-signal attenuation prevents military submarines and underground surveying operations from taking advantage of GPS location, and can cause GPS to cut out in the dense, skyscraper-lined canyons of urban downtowns. And it can block wireless communication among first responders picking their way through debris or rubble-cluttered disaster scenes.

    Technically, those limitations relate to a quantity known as the skin depth—the depth in a material at which an AC electromagnetic field becomes attenuated to 1/e of its original strength. The skin depth is inversely proportional to the square root of the signal frequency (as well as the conductivity and relative permeability of the material the electromagnetic field is trying to penetrate). That means, for a given material, that the penetration depth for a signal in the gigahertz (GHz) band typical of modern wireless communications can be three orders of magnitude smaller than for a VLF channel in the kilohertz (kHz) range.

    An obvious way to address the skin-depth issue is to communicate at very low frequencies. But those frequencies have their own problems. The biggest is extremely limited bandwidth, which rules out data-intensive applications like position detection or video. Another problem is the large antennas required to pull in the faint VLF signals using conventional receiving equipment. As a result, while the VLF band is now used for communications with submarines underwater, the data exchange amounts to little more than text messages—and, to receive them, the sub must spool out a long antenna and rise to periscope depth.

    A quantum solution

    The NIST team, led by researcher Dave Howe, has proposed a solution to VLF’s sensitivity problems: Encode the modulated signal on low-frequency magnetic fields—and then reconfigure the new generation of ultrasensitive magnetometers that’s emerging from quantum technology as magnetic-radio receivers. This would push the receiver’s ability to pick up VLF communications far beyond that of conventional RF receivers. And, the team suggests, picking the right modulation scheme for encoding the signal could hammer down ambient noise, allowing the best possible use of the available bandwidth in these low-frequency chanels.

    The specific quantum sensor used by Howe’s team is an optically pumped magnetometer (OPM). These devices, typically employed to measure faint natural magnetic fields, are a bit more robust than alternatives such as superconducting quantum interference devices (SQUID), as OPMs can work at room temperature and have low size, power and cost requirements.

    2
    The optically pumped magnetometer (OPM) setup in the work by Howe’s NIST group. PD, photodiode; PBS, polarizing beamsplitter; L, lock-in amplifier. DC, ZF and SO refer to the magnetometer’s three operating modes: direct current, zero field, and self-oscillating. Photo at right shows the size of the rubidium atom vapor cell. [Image: Reprinted from V. Gerginov et al., Rev. Sci. Instr. 88, 125005 (2017), with the permission of AIP Publishing]

    The instrument used by the NIST scientists works by firing pump and probe lasers into a vapor cell containing isotopically pure 87Rb atoms. Changes in the quantum spin of the atom ensemble due to an external, signal-carrying modulated DC magnetic field result in changes in the probe light’s polarization as it passes through the ensemble. Those changes, in turn, are read out at a balanced polarimeter at the end of the chain, and converted into AC signals to decode the magnetic-radio signal.

    Meanwhile, on the transmission side, the team found that it could significantly reduce the impact of environmental noise—and, thus, boost the low-frequency signal’s carrying capacity—by adopting a digital binary phase-shift keying (BPSK) modulation scheme for the low-frequency magnetic-field signal. In particular, the BPSK modulation designed by the team had the effect of suppressing noise sources such as Earth’s natural magnetic background and the 50/60-Hz hum (plus harmonics) from the electrical power grid.

    Picotesla sensitivity

    In a proof of principle, the NIST researchers created a simple, single-channel digitally encoded DC magnetic signal, and found that the OPM setup could detect the faint, sub-kHz-frequency signal at picotesla field strengths, far below the ambient magnetic background noise, across a distance spanning tens of meters in the magnetically noisy indoor NIST setting. The team believes that range could be extended further, to the hundreds of meters, in less noisy environments, and through continued improvements both in sensor technology and signal modulation.

    On that head, Howe’s group is working on a new custom quantum magnetometer that can provide still greater sensitivity, and on other techniques to reduce noise and expand bandwidth. In a press release, Howe likened the combining of quantum sensor technology and low-frequency magnetic radio to “inventing an entirely new field.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Optics & Photonics News (OPN) is The Optical Society’s monthly news magazine. It provides in-depth coverage of recent developments in the field of optics and offers busy professionals the tools they need to succeed in the optics industry, as well as informative pieces on a variety of topics such as science and society, education, technology and business. OPN strives to make the various facets of this diverse field accessible to researchers, engineers, businesspeople and students. Contributors include scientists and journalists who specialize in the field of optics. We welcome your submissions.

     
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