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  • richardmitnick 1:29 pm on September 17, 2020 Permalink | Reply
    Tags: "Stanford researchers devise way to see through clouds and fog", A highly efficient algorithm that can reconstruct three-dimensional hidden scenes based on the movement of individual particles of light or photons., , , LIDAR – Light Detection and Ranging, ,   

    From Stanford University: “Stanford researchers devise way to see through clouds and fog” 

    Stanford University Name
    From Stanford University

    September 9, 2020
    Taylor Kubota
    (650) 724-7707
    tkubota@stanford.edu

    Like a comic book come to life, researchers at Stanford University have developed a kind of X-ray vision – only without the X-rays. Working with hardware similar to what enables autonomous cars to “see” the world around them, the researchers enhanced their system with a highly efficient algorithm that can reconstruct three-dimensional hidden scenes based on the movement of individual particles of light, or photons. In tests, detailed in a paper published Sept. 9 in Nature Communications, their system successfully reconstructed shapes obscured by 1-inch-thick foam. To the human eye, it’s like seeing through walls.

    Imaging through scattering media
    1
    Schematic of 3D Imaging through scattering media. a A pulsed laser and time resolved single-photon detector raster-scan the surface of the scattering medium. b Light diffuses through the medium, is back-reflected by the hidden object, and diffuses back through the medium to the detector. c Returning photons from the hidden object are captured by the detector over time, with earlier arriving photons being gated out (dashed line). SG, scanning galvanometer; BS, beam splitter; OL, objective lens; SPAD, single-photon avalanche diode; TCSPC, time-correlated single-photon counter.


    Abstract
    Optical imaging techniques, such as light detection and ranging (LiDAR), are essential tools in remote sensing, robotic vision, and autonomous driving. However, the presence of scattering places fundamental limits on our ability to image through fog, rain, dust, or the atmosphere. Conventional approaches for imaging through scattering media operate at microscopic scales or require a priori knowledge of the target location for 3D imaging. We introduce a technique that co-designs single-photon avalanche diodes, ultra-fast pulsed lasers, and a new inverse method to capture 3D shape through scattering media. We demonstrate acquisition of shape and position for objects hidden behind a thick diffuser (≈6 transport mean free paths) at macroscopic scales. Our technique, confocal diffuse tomography, may be of considerable value to the aforementioned applications.

    “A lot of imaging techniques make images look a little bit better, a little bit less noisy, but this is really something where we make the invisible visible,” said Gordon Wetzstein, assistant professor of electrical engineering at Stanford and senior author of the paper. “This is really pushing the frontier of what may be possible with any kind of sensing system. It’s like superhuman vision.”

    This technique complements other vision systems that can see through barriers on the microscopic scale – for applications in medicine – because it’s more focused on large-scale situations, such as navigating self-driving cars in fog or heavy rain and satellite imaging of the surface of Earth and other planets through hazy atmosphere.

    Supersight from scattered light

    In order to see through environments that scatter light every-which-way, the system pairs a laser with a super-sensitive photon detector that records every bit of laser light that hits it. As the laser scans an obstruction like a wall of foam, an occasional photon will manage to pass through the foam, hit the objects hidden behind it and pass back through the foam to reach the detector. The algorithm-supported software then uses those few photons – and information about where and when they hit the detector – to reconstruct the hidden objects in 3D.

    4
    The laser scanning process in action. Single photons that travel through the foam, bounce off the “S,” and back through the foam to the detector provide information for the algorithm’s reconstruction of the hidden object. (Image credit: Stanford Computational Imaging Lab)

    This is not the first system with the ability to reveal hidden objects through scattering environments, but it circumvents limitations associated with other techniques. For example, some require knowledge about how far away the object of interest is. It is also common that these systems only use information from ballistic photons, which are photons that travel to and from the hidden object through the scattering field but without actually scattering along the way.

    “We were interested in being able to image through scattering media without these assumptions and to collect all the photons that have been scattered to reconstruct the image,” said David Lindell, a graduate student in electrical engineering and lead author of the paper. “This makes our system especially useful for large-scale applications, where there would be very few ballistic photons.”

    In order to make their algorithm amenable to the complexities of scattering, the researchers had to closely co-design their hardware and software, although the hardware components they used are only slightly more advanced than what is currently found in autonomous cars. Depending on the brightness of the hidden objects, scanning in their tests took anywhere from one minute to one hour, but the algorithm reconstructed the obscured scene in real-time and could be run on a laptop.

    “You couldn’t see through the foam with your own eyes, and even just looking at the photon measurements from the detector, you really don’t see anything,” said Lindell. “But, with just a handful of photons, the reconstruction algorithm can expose these objects – and you can see not only what they look like, but where they are in 3D space.”

    Space and fog

    5
    A three-dimensional reconstruction of the reflective letter “S,” as seen through the 1-inch-thick foam. (Image credit: Stanford Computational Imaging Lab)

    Someday, a descendant of this system could be sent through space to other planets and moons to help see through icy clouds to deeper layers and surfaces. In the nearer term, the researchers would like to experiment with different scattering environments to simulate other circumstances where this technology could be useful.

    “We’re excited to push this further with other types of scattering geometries,” said Lindell. “So, not just objects hidden behind a thick slab of material but objects that are embedded in densely scattering material, which would be like seeing an object that’s surrounded by fog.”

    Lindell and Wetzstein are also enthusiastic about how this work represents a deeply interdisciplinary intersection of science and engineering.

    “These sensing systems are devices with lasers, detectors and advanced algorithms, which puts them in an interdisciplinary research area between hardware and physics and applied math,” said Wetzstein. “All of those are critical, core fields in this work and that’s what’s the most exciting for me.”

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    Stanford University campus. No image credit

    Stanford University

    Leland and Jane Stanford founded the University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members

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  • richardmitnick 2:42 pm on August 20, 2020 Permalink | Reply
    Tags: "Stanford scientists slow and steer light with resonant nanoantennas", , “High-Q” resonators, Biosensing, , LIDAR – Light Detection and Ranging, , , ,   

    From Stanford University: Women in STEM-“Stanford scientists slow and steer light with resonant nanoantennas” Jennifer Dionne 

    Stanford University Name
    From Stanford University

    August 17, 2020
    Media Contact
    Ker Than
    Stanford News Service:
    (650) 723-9820
    kerthan@stanford.edu

    Written By Lara Streiff

    Researchers have fashioned ultrathin silicon nanoantennas that trap and redirect light, for applications in quantum computing, LIDAR and even the detection of viruses.

    1
    An artist rendering of a high-Q metasurface beamsplitter. These “high-quality-factor” or “high-Q” resonators could lead to novel ways of manipulating and using light. (Image credit: Riley A. Suhar)

    Light is notoriously fast. Its speed is crucial for rapid information exchange, but as light zips through materials, its chances of interacting and exciting atoms and molecules can become very small. If scientists can put the brakes on light particles, or photons, it would open the door to a host of new technology applications.

    Now, in a paper published on Aug. 17, in Nature Nanotechnology, Stanford scientists demonstrate a new approach to slow light significantly, much like an echo chamber holds onto sound, and to direct it at will. Researchers in the lab of Jennifer Dionne, associate professor of materials science and engineering at Stanford, structured ultrathin silicon chips into nanoscale bars to resonantly trap light and then release or redirect it later. These “high-quality-factor” or “high-Q” resonators could lead to novel ways of manipulating and using light, including new applications for quantum computing, virtual reality and augmented reality; light-based WiFi; and even the detection of viruses like SARS-CoV-2.

    “We’re essentially trying to trap light in a tiny box that still allows the light to come and go from many different directions,” said postdoctoral fellow Mark Lawrence, who is also lead author of the paper. “It’s easy to trap light in a box with many sides, but not so easy if the sides are transparent – as is the case with many Silicon-based applications.”

    Make and manufacture

    Before they can manipulate light, the resonators need to be fabricated, and that poses a number of challenges.

    A central component of the device is an extremely thin layer of silicon, which traps light very efficiently and has low absorption in the near-infrared, the spectrum of light the scientists want to control. The silicon rests atop a wafer of transparent material (sapphire, in this case) into which the researchers direct an electron microscope “pen” to etch their nanoantenna pattern. The pattern must be drawn as smoothly as possible, as these antennas serve as the walls in the echo-chamber analogy, and imperfections inhibit the light-trapping ability.

    “High-Q resonances require the creation of extremely smooth sidewalls that don’t allow the light to leak out,” said Dionne, who is also Senior Associate Vice Provost of Research Platforms/Shared Facilities. “That can be achieved fairly routinely with larger micron-scale structures, but is very challenging with nanostructures which scatter light more.”

    Pattern design plays a key role in creating the high-Q nanostructures. “On a computer, I can draw ultra-smooth lines and blocks of any given geometry, but the fabrication is limited,” said Lawrence. “Ultimately, we had to find a design that gave good-light trapping performance but was within the realm of existing fabrication methods.”

    High quality (factor) applications

    Tinkering with the design has resulted in what Dionne and Lawrence describe as an important platform technology with numerous practical applications.

    The devices demonstrated so-called quality factors up to 2,500, which is two orders of magnitude (or 100 times) higher than any similar devices have previously achieved. Quality factors are a measure describing resonance behavior, which in this case is proportional to the lifetime of the light. “By achieving quality factors in the thousands, we’re already in a nice sweet spot from some very exciting technological applications,” said Dionne.

    For example, biosensing. A single biomolecule is so small that it is essentially invisible. But passing light over a molecule hundreds or thousands of times can greatly increase the chance of creating a detectable scattering effect.

    Dionne’s lab is working on applying this technique to detecting COVID-19 antigens – molecules that trigger an immune response – and antibodies – proteins produced by the immune system in response. “Our technology would give an optical readout like the doctors and clinicians are used to seeing,” said Dionne. “But we have the opportunity to detect a single virus or very low concentrations of a multitude of antibodies owing to the strong light-molecule interactions.” The design of the high-Q nanoresonators also allows each antenna to operate independently to detect different types of antibodies simultaneously.

    Though the pandemic spurred her interest in viral detection, Dionne is also excited about other applications, such as LIDAR – or Light Detection and Ranging, which is laser-based distance measuring technology often used in self-driving vehicles – that this new technology could contribute to. “A few years ago I couldn’t have imagined the immense application spaces that this work would touch upon,” said Dionne. “For me, this project has reinforced the importance of fundamental research – you can’t always predict where fundamental science is going to go or what it’s going to lead to, but it can provide critical solutions for future challenges.”

    This innovation could also be useful in quantum science. For example, splitting photons to create entangled photons that remain connected on a quantum level even when far apart would typically require large tabletop optical experiments with big expensive precisely polished crystals. “If we can do that, but use our nanostructures to control and shape that entangled light, maybe one day we will have an entanglement generator that you can hold in your hand,” Lawrence said. “With our results, we are excited to look at the new science that’s achievable now, but also trying to push the limits of what’s possible.”

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    Stanford University campus. No image credit

    Stanford University

    Leland and Jane Stanford founded the University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members

    Stanford University Seal

     
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