MSGID: 1:317/3 6274a4a6   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    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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