• Researchers create flat magic window wit

    From ScienceDaily@1:317/3 to All on Thu May 5 22:30:38 2022
    Researchers create flat magic window with liquid crystals
    Inspired by an ancient light trick, technology could enable a new type of
    3D display

    Date:
    May 5, 2022
    Source:
    Optica
    Summary:
    Researchers have used liquid crystals to create a flat magic window
    -- a transparent device that produces a hidden image when light
    shines on it.

    The process for creating transparent liquid crystal magic windows
    can produce any desired image. The process can also be used to
    create magic mirrors that reflect, rather than transmit, light to
    create an image. The technology represents a new twist on a very old
    light trick, originating thousands of years ago in China and Japan.



    FULL STORY ==========================================================================
    For the first time, researchers have used liquid crystals to create a
    flat magic window -- a transparent device that produces a hidden image
    when light shines on it. The technology represents a new twist on a very
    old light trick.


    ========================================================================== Thousands of years ago, artisans in China and Japan made bronze mirrors
    that looked like a normal flat mirror while viewing one's reflection but
    formed another image when hit by direct sunlight. It took until the early
    20th century for scientists to understand that these devices work because
    an image cast into the back of the mirror creates small surface variations
    that cause the image to form -- and it took until now for engineers to
    apply the same principle to liquid crystals for high-tech displays.

    "The magic window we created appears perfectly flat to the naked eye
    but, in fact, has slight variations that create an image in response to
    light," said research team leader Felix Hufnagel from the University of
    Ottawa. "By designing the window to be relatively smooth, the image that
    is created can be seen over a large range of distances from the window."
    In Optica, Hufnagel and colleagues describe the process they developed
    for creating transparent liquid crystal magic windows that can produce
    any desired image. The process can also be used to create magic mirrors
    that reflect, rather than transmit, light to create an image.

    "Using liquid crystals to make magic windows or mirrors could one day
    make it possible to create a reconfigurable version for producing dynamic artistic magic windows or movies," said Hufnagel. "The ability to obtain
    a long depth of focus could also make the approach useful for 3D displays
    that produce stable 3D images even when viewed from different distances." Creating magic with liquid crystals Although scientists have understood
    for decades that the ancient bronze magic mirrors formed images as a
    result of small surface variations, it was not until 2005 that Michael
    Berry, a mathematical physicist at the University of Bristol in the UK,
    derived the mathematical basis for this effect. He later extended this knowledge to develop a theoretical basis for transparent magic windows
    in addition to reflective magic mirrors. This work inspired Hufnagel
    and colleagues to create a magic window based on liquid crystals.



    ========================================================================== Liquid crystals are materials that can flow like a conventional liquid
    but have molecules that can be oriented like a solid crystal. In the new
    work, the researchers used a modified version of a well-known fabrication process that produces a specific liquid crystal pattern that allows a
    desired image to be created when illuminated.

    They used a Pancharatnam-Berry Optical Element (PBOE), which is a liquid crystal device that operates under a well-known principle called the Pancharatnam-Berry phase. By changing the orientation of liquid crystal molecules in this device, the researchers could alter the properties of
    the light as it travels through the device on a pixel-by-pixel basis.

    Stable images over multiple distances "On a conceptual level, the theory developed by Berry was instrumental in determining how these liquid
    crystals must be oriented to create an image that is stable over a large distance," said Hufnagel. "Our use of flat optical elements and a liquid crystal pattern with gentle variations prescribed by Berry's Laplacian
    image theory allows the magic windows to appear normal, or flat, when one
    looks through them." After fabricating a magic mirror and window, the researchers used a camera to measure the light intensity patterns produced
    by both devices. When illuminated with a laser beam, both the mirror and
    window produced a visible image that remained stable even as the distance between the camera and the mirror or window changed. The researchers also showed that the devices created images when illuminated with an LED light source, which would be more practical to use in real-life applications.

    The researchers are now working to use their fabrication approach to
    create quantum magic plates. For example, two of these plates could
    create entangled images which one could use to study new quantum imaging protocols. They are also exploring the possibility of fabricating magic
    windows using approaches other than liquid crystals. For instance, using dielectric metasurfaces to make a magic window device could reduce its footprint while increasing bandwidth.


    ========================================================================== Story Source: Materials provided by Optica. Note: Content may be edited
    for style and length.


    ========================================================================== Journal Reference:
    1. Felix Hufnagel, Alessio D'Errico, Hugo Larocque, Fatimah Alsaiari,
    Jeremy
    Upham, Ebrahim Karimi. Flat magic window. Optica, 2022; 9 (5):
    479 DOI: 10.1364/OPTICA.454293 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/05/220505102149.htm

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