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  • richardmitnick 1:59 am on October 9, 2021 Permalink | Reply
    Tags: "FAU physicists control the flow of electron pulses through a nanostructure channel", APF: alternating phase focusing, , , DLA uses ultra-fast laser technology and advances in semi-conductor production to potentially minimise these accelerators to merely a few millimetres or centimetres in size., DLA: dielectric laser acceleration, , Nanophotonics, , ,   

    From Friedrich-Alexander-Universität Erlangen-Nürnberg [FAU] (DE): “FAU physicists control the flow of electron pulses through a nanostructure channel” 

    From Friedrich-Alexander-Universität Erlangen-Nürnberg [FAU] (DE)

    September 23, 2021

    Chair for Laser Physics
    Dr. Roy Shiloh
    Tel.: 09131/85-27211
    roy.shiloh@fau.de

    Johannes Illmer M.Sc.
    Tel.: 09131/85-27211
    johannes.i.illmer@fau.de

    Prof. Dr. Peter Hommelhoff
    Tel.: 09131/85-27090
    peter.hommelhoff@fau.de

    1
    Experimental setup in the laser laboratory. Picture: Maximilian Schlosser.

    Particle accelerators are essential tools in research areas such as biology, materials science and particle physics. Researchers are always looking for more powerful ways of accelerating particles to improve existing equipment and increase capacities for experiments. One such powerful technology is dielectric laser acceleration (DLA). In this approach, particles are accelerated in the optical near-field which is created when ultra-short laser pulses are focused on a nanophotonic structure. Using this method, researchers from the Chair of Laser Physics at FAU have succeeded in guiding electrons through a vacuum channel, an essential component of particle accelerators. The basic design of the photonic nanostructure channel was developed by cooperation partner The Technical University of Darmstadt [Technische Universität Darmstadt] (DE). They have now published their joint findings in the journal Nature.

    Staying focused

    As charged particles tend to move further away from each other as they spread, all accelerator technologies face the challenge of keeping the particles within the required spatial and time boundaries. As a result, particle accelerators can be up to ten kilometres long, and entail years of preparation and construction before they are ready for use, not to mention the major investments involved. Dielectric laser acceleration, or DLA uses ultra-fast laser technology and advances in semi-conductor production to potentially minimise these accelerators to merely a few millimetres or centimetres in size.

    A promising approach: Experiments have already demonstrated that DLA exceeds currently used technologies by at least 35 times. This means that the length of a potential accelerator could be reduced by the same factor. Until now, however, it was unclear whether these figures could be scaled up for longer and longer structures.

    A team of physicists led by Prof. Dr. Peter Hommelhoff from the Chair of Laser Physics at FAU has taken a major step forward towards adapting DLA for use in fully-functional accelerators. Their work is the first to set out a scheme which can be used to guide electron pulses over long distances.

    Technology is key

    The scheme, known as ‘alternating phase focusing’ (APF) is a method taken from the early days of accelerator theory. A fundamental law of physics means that focusing charged particles in all three dimensions at once – width, height and depth – is impossible. However, this can be avoided by alternately focusing the electrons in different dimensions. First of all, electrons are focused using a modulated laser beam, then they ‘drift’ through another short passage where no forces act on them, before they are finally accelerated, which allows them to be guided forward.

    In their experiment, the scientists from FAU and TU Darmstadt incorporated a colonnade of oval pillars with short gaps at regular intervals, resulting in repeating macro cells. Each macro cell either has a focusing or defocusing effect on the particles, depending on the delay between the incident laser, the electron, and the gap which creates the drifting section. This setup allows precise electron phase space control at the optical or femto-second ultra-timescale (a femto-second corresponds to a millionth of a billionth of a second). In the experiment, shining a laser on the structure shows an increase in the beam current through the structure. If a laser is not used, the electrons are not guided and gradually crash into the walls of the channel. ‘It’s very exciting,’ says FAU physicist Johannes Illmer, co-author of the publication. ‘By way of comparison, the large Hadron collider at CERN uses 23 of these cells in a 2450 metre long curve. Our nanostructure uses five similar-acting cells in just 80 micrometres.’

    When can we expect to see the first DLA accelerator?

    ‘The results are extremely significant, but for us it is really just an interim step,’ explains Dr. Roy Shiloh, ‘and our final goal is clear: we want to create a fully-functional accelerator – on a microchip.’

    See the full article here.

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Friedrich-Alexander-Universität Erlangen-Nürnberg, [FAU] (DE} is a public research university in the cities of Erlangen and Nuremberg in Bavaria, Germany. The name Friedrich–Alexander comes from the university’s first founder Friedrich, Margrave of Brandenburg-Bayreuth, and its benefactor Christian Frederick Charles Alexander, Margrave of Brandenburg-Ansbach.

    FAU is the second largest state university in the state of Bavaria. It has 5 faculties, 24 departments/schools, 25 clinical departments, 21 autonomous departments, 579 professors, 3,457 members of research staff and roughly 14,300 employees.

    In winter semester 2018/19 around 38,771 students (including 5,096 foreign students) enrolled in the university in 265 fields of study, with about 2/3 studying at the Erlangen campus and the remaining 1/3 at the Nuremberg campus. These statistics put FAU in the list of top 10 largest universities in Germany. In 2018, 7,390 students graduated from the university and 840 doctorates and 55 post-doctoral theses were registered. Moreover, FAU received 201 million Euro (2018) external funding in the same year, making it one of the strongest third-party funded universities in Germany.

    FAU is also a member of DFG (Deutsche Forschungsgemeinschaft) and the Top Industrial Managers for Europe network.

     
  • richardmitnick 4:33 pm on March 11, 2019 Permalink | Reply
    Tags: , How bright can the radiation from a single molecule be? How quickly can a hot body cool off? And what materials should one choose to maximize these effects?, Nanophotonics, , The findings could open the way for brighter imaging techniques improved solar-power technologies and the efficient conversion of heat to electricity., This “new global optimum” is expected to help scientists understand the potential for light-matter interaction for any material unlocking the future development of promising practical applications,   

    From Yale University: “Yale physicists light the way for new technology discoveries” 

    Yale University bloc

    From Yale University

    March 11, 2019
    Jon Atherton

    1

    Enshrined by the laws of Austrian physicists Josef Stefan and Ludwig Boltzmann in the late 19th Century, scientists have long understood the general principles of heat-energy transfer between the sun and planet Earth.

    But at much closer separations, where photons can effectively “tunnel” between two bodies, the maximum rate and size at which two objects – one hot, one cold – can transfer heat has remained unknown.

    From their emerging field of near-field nanophotonics, a group of Yale scientists have taken a new step in advancing the ‘Stefan-Boltzmann law’ by creating a mathematical framework to identify the upper bounds of light interactions and radiative energy transfer.

    Their findings could open the way for brighter imaging techniques, improved solar-power technologies, and the efficient conversion of heat to electricity.

    Writing in the journal Physical Review X, scholars at the Yale Energy Sciences Institute set out to answer fundamental questions: how bright can the radiation from a single molecule be? How quickly can a hot body cool off? And what materials should one choose to maximize these effects?

    To understand spontaneous emissions in the “near field,” where radiating sources are close to structured materials, graduate student Hyungki Shim developed mathematical techniques to strip away the complex dynamics in these large design spaces, revealing instead the key physical principles constraining optical response.

    Alongside summer student Lingling Fan, MIT professor Steven Johnson, and the study’s senior author Owen Miller, an assistant professor in the Department of Applied Physics, the scholars developed the first singular metric to measure light interactions.

    In the race to discover new two dimensional materials to power technology innovations, this “new global optimum” is expected to help scientists understand the potential for light-matter interaction for any material, unlocking the future development of promising practical applications.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Yale University Campus

    Yale University comprises three major academic components: Yale College (the undergraduate program), the Graduate School of Arts and Sciences, and the professional schools. In addition, Yale encompasses a wide array of centers and programs, libraries, museums, and administrative support offices. Approximately 11,250 students attend Yale.

     
  • richardmitnick 6:03 pm on July 3, 2017 Permalink | Reply
    Tags: Delbrück scattering, , Nanophotonics, , Polarized gamma rays, , , The future Extreme Light Infrastructure in Măgurele Romania, Vacuum studies, Werner Heisenberg's Uncertainty Principle   

    From Inside Science via Don Lincoln at FNAL: “A Study About Nothing” 

    Inside Science

    June 29, 2017
    Yuen Yiu

    1
    Image credits: Abigail Malate

    Scientists find new ways to measure the infinitesimally small fluctuations that exist in a vacuum.

    A vacuum is a space absolutely devoid of matter, at least according to the Merriam-Webster dictionary. But if you talk to a physicist you may get a different answer. According to quantum physics, even vacuums are not completely empty. Constant fluctuations in energy can spontaneously create mass not just out of thin air, but out of absolutely nothing at all.

    “It’s like a boiling sea of appearing and disappearing particle pairs,” said James Koga, a theoretical physicist from the National Institutes for Quantum and Radiological Science and Technology in Kyoto, Japan. The pairs, made up of one particle and one antiparticle, exist for only moments. Koga is investigating the subtle effects caused by these fluctuations.

    This peculiar nature of vacuum, sometimes referred to as “quantum vacuum,” is not just theoretical speculation. It has real, measurable effects on our physical reality. Although these effects are usually far too small to impact even the most sensitive instruments of today, scientists think the picture will change for the miniaturized technologies of tomorrow.

    “In the macroscopic world, we don’t care about these forces at all. You wouldn’t care about it when you are driving a car for instance. It’s totally negligible,” said Alejandro Manjavacas, a physicist specializing in photonics at the University of New Mexico in Albuquerque. “But in the context of nanotechnology or nanophotonics — at a super small scale, these effects will start playing a role.”

    Although the concept of a fluctuating vacuum was theorized and proven during the first half of the last century, scientists are still grappling with the implications. Two recently published papers explore two separate aspects of the same mystery — what happens when there is nothing at all?

    A glistening ocean

    The energy fluctuation in vacuum can be explained by the uncertainty principle of quantum physics. The principle, first introduced by German physicist Werner Heisenberg, states that at any definite point in space, there must exist temporary changes in energy over time. Sometimes this energy is converted into mass, generating particle-antiparticle pairs.

    Most of the time these newly born pairs recombine and vanish before interacting with anything. Because of this, physicists like to refer to these pairs as “virtual particles,” but this doesn’t mean they aren’t real — they just need something to interact with to make their presence felt.

    For this, Koga and his team envision a way to observe this boiling sea of vacuum the same way we see glistening waves in the ocean — with light. In their latest paper, published in Physical Review Letters, they lay down the theoretical groundwork needed for the experiment. Specifically, they want to study photons that bounce off an atomic nucleus in a distinctive way that wouldn’t happen without the “boiling” vacuum acting as the middleman. This peculiar light phenomenon is known as Delbrück scattering, predicted by German-American physicist Max Delbrück in 1933. The effect was later observed experimentally in 1975 — but just barely.

    “[Scientists] could kind of guess that the Delbrück scattering was there, but it was like if you include this effect in your calculation then it agrees more with the data,” said Koga.

    Koga and his team hope to take Delbrück scattering to another level by characterizing the phenomenon’s effect. It is as if scientists knew about air resistance, but still needed to study it further so that engineers could use the knowledge to build an airplane.

    The task is tricky. To measure Delbrück scattering, one must shine light onto trillions of atomic nuclei, which creates a problem. Photons bounce off nuclei, electrons and even each other in all directions, via all kinds of different interactions. How can one distinguish which photon is scattered from what?

    Koga’s team suggests that we use polarized gamma rays. Just like polarized sunglasses can help you see better by filtering out unwanted solar glares, polarized gamma rays can help scientists sift through the gazillions of photons based on their polarization, in addition to energy and scattered angle. As long as one knows where to look for the specific photons that are the results of Delbrück scattering, one should be able to pick them out from the lineup.

    “The point that we are trying to make in our paper is by using a new polarized source, you can almost see the signal isolated,” said Koga.

    But there is just one problem — such an instrument doesn’t exist. At least not yet.

    Enter the future Extreme Light Infrastructure in Măgurele, Romania. This facility will not only provide the polarized gamma rays Koga proposed, but will make some of the brightest gamma rays in the world. This is important because just like a brighter ambient light can shorten the exposure time for taking a photo, a brighter gamma ray can shorten the run time for Koga’s proposed experiment.


    Credit: ELI-NP Romania

    Kazuo Tanaka, the scientific director of the Nuclear Physics division of the future facility, is pleased with Koga’s team’s proposal.

    “I think their proposal is very crystal clear. They calculated how many days of shooting they need for the experiment, and came up with 76 days,” he said. “I think if they do the experiment we can have a very definitive measurement for Delbrück scattering.”

    While the facility is still under construction, and will not be ready for the experiment at least until 2019, a different group of physicists are studying the same nothingness of vacuum, but with a different set of eyes. Instead of beaming light into the vacuum and looking for a glint, physicist Alejandro Manjavacas and his group at the University of New Mexico want to know if the fluctuations of vacuum can actually exert an invisible force on physical objects — as if they were being moved by Jedis.


    The video shows two plates moving towards each other in a vibrating pool of water, an analogy to the Casimir effect that exist in a fluctuating vacuum. Credit: Denysbondar

    The Casimir effect, named after Dutch physicist Henrik Casimir, describes the force that pushes two objects together due to surrounding waves. The effect exists for two beads on a vibrating string, or two boats in a wavy ocean, as well as two particles in a fluctuating vacuum. Much like Delbrück scattering, the Casimir effect was theorized in 1948 and has already been confirmed, in 1996. So, what is left to be discovered?

    “Most of the work that was done on Casimir effect was for systems that weren’t moving, or if they were moving, they were moving in a uniform motion,” said Manjavacas.

    In a paper published in Physical Review Letters, Manjavacas and his colleagues calculated how the Casimir effect can nudge objects that are already spinning and moving. Through calculations, they discovered that when a tiny sphere spins near a flat surface, it will move as if it is rolling down the surface, despite never making contact with it.

    “If you try to make a nanostructure that involves moving parts that are very close together, it is crucial to know what is going to be the effect from these type of forces. You’ll need to know whether it is going to cause the moving parts to get stuck,” said Manjavacas. “Or we can use these forces to our advantage, such as using them to move objects or to force them to do the things that we want.”

    In their study, the researchers evaluated the effect for spheres with diameters ranging from 50 to 500 nanometers, much less than one hundredth the width of a human hair. As expected, the relationship between the spinning and the lateral movement isn’t straightforward — it depends on the speed that the sphere is spinning, as well as the size of the sphere and the distance between the sphere and the surface. These minute effects may soon be relevant on the frontier of technology, for example when engineers design medical nanobots.

    2
    Virtual Particles and Black Holes
    The sidebar image shows a simulated animation of a black hole moving across a galaxy in the background. Credit: Wikicommons/CC BY-SA 3.0
    Even though the quantum interpretation of vacuum — complete with strange particles popping into and out of existence — accurately describes our reality, how can we tell that this isn’t just another placeholder theory? Will the theory eventually fail just like the geocentric model, or the flat earth model, or perhaps most relevantly, the famous failed theory of ether from the 19th century?
    The theory of ether was proposed by physicists to explain how light waves can propagate through the vacuum of space. Based on intuition, scientists back then believed that a medium was necessary for light waves to travel, just like the waves in the ocean travel through the medium of water. This hypothesis was disproved in 1887 by Albert Michelson and Edward Morley, in a famous experiment, in which they measured the speed of light in perpendicular directions and found no difference. Albert Michelson was later awarded a Nobel Prize in 1907 for his achievements, and became the first Nobel laureate from the United States.

    So, will the quantum model of vacuum also be proved wrong? Most physicists today do not think so. In fact, Nobel laureate Robert Laughlin from Stanford University has written in his book “A Different Universe: Reinventing Physics from the Bottom Down” specifically about this comparison: “The word [ether] has extremely negative connotations in theoretical physics because of its past association with opposition to relativity. This is unfortunate because, stripped of these connotations, it

    Beyond its impact on nanotechnologies and particle accelerators here on earth, the fluctuating vacuum extends its effects into space. In 1968, British astrophysicist Stephen Hawking predicted that when a particle-antiparticle pair is created on the edge of a black hole’s event horizon, the pair can be pried apart by gravity — one particle falling into the black hole and the other escaping. The escape of one of the particles then contributes to an infinitesimally small, and so far purely theoretical, radiation known as Hawking radiation.
    Hawking radiation, if proven, will play a crucial role in determining the lifetime of black holes. However, even if the radiation is real, it will still be far too faint for us to detect it. There have been a few analogous models that can successfully reproduce the phenomenon in a laboratory setting, but they use light waves or sound waves instead of gravitational waves of black holes. There is hope that the Large Hadron Collider near Geneva, Switzerland, with a higher energy output, can create a super tiny black hole that lasts but a split second, and offer a more definitive answer on Hawking radiation. But for now, no direct observation for Hawking radiation has been possible, leading to some saying that the “jury is still out.”
    “This is a pity, because if they had, I would have got a Nobel prize,” said Hawking during a 2008 lecture.

    A real virtuality

    Even though the quantum interpretation of vacuum — complete with strange particles popping into and out of existence — accurately describes our reality, how can we tell that this isn’t just another placeholder theory? Will the theory eventually fail just like the geocentric model, or the flat earth model, or perhaps most relevantly, the famous failed theory of ether from the 19th century?

    The theory of ether was proposed by physicists to explain how light waves can propagate through the vacuum of space. Based on intuition, scientists back then believed that a medium was necessary for light waves to travel, just like the waves in the ocean travel through the medium of water. This hypothesis was disproved in 1887 by Albert Michelson and Edward Morley, in a famous experiment, in which they measured the speed of light in perpendicular directions and found no difference. Albert Michelson was later awarded a Nobel Prize in 1907 for his achievements, and became the first Nobel laureate from the United States.

    So, will the quantum model of vacuum also be proved wrong? Most physicists today do not think so. In fact, Nobel laureate Robert Laughlin from Stanford University has written in his book “A Different Universe: Reinventing Physics from the Bottom Down” specifically about this comparison: “The word [ether] has extremely negative connotations in theoretical physics because of its past association with opposition to relativity. This is unfortunate because, stripped of these connotations, it rather nicely captures the way most physicists actually think about the vacuum.”

    Because unlike the ether theory, the quantum model of vacuum, with all its fluctuations and peculiar features, has since been thoroughly tested and proven.

    “We see pair creation all the time actually, like in particle accelerators,” said Koga. In fact, it happens so often that for certain experiments scientists actually have to consider the phenomenon as “noise” that could obscure the signal they are looking for, according to Koga.

    “We now have experimental evidence of all kinds of particles coming in and out [of the vacuum],” said Toshiki Tajima, a physicist from the University of California, Irvine. “Muons and anti-muons, protons and anti-protons, and even quarks and anti-quarks.”

    In 1665, Robert Hooke and Antoni van Leeuwenhoek discovered microbes when they pointed their microscopes at “nothing.” In 1964, Arno Penzias and Robert Woodrow Wilson discovered the cosmic microwave background when they pointed their telescopes at “nothing.” Vacuum is perhaps the ultimate “nothing,” so if history is any indication, “nothing” is an interesting place, especially if you want to look for something.

    See the full article here .

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    Inside Science is brought to you in part through the generous support of The American Physical Society and The Acoustical Society of America and a coalition of underwriters.

     
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