Current consumer holograms are not "true" freestanding holograms. Essentially, what we have today is a photographic recording of a light field, instead of a lens-formed image. These holograms are capable of being produced in a 3D manner with both perspective and parallax, giving the images a realistic change with regards to the perspective of the observer.
Recently, there have been a few major breakthroughs in holographic technologies to bring us one step closer to its sci-fi counterpart.
The World's Thinnest Hologram
A research paper published earlier this week discusses the work of a team of researchers that have been able to successfully produce the world’s thinnest hologram. The researchers, headed by Professor Min Gu from RMIT University in Melbourne, Australia, and members from the Beijing Institute of Technology claim they were able to create a hologram from a surface just nanometers thick.
Traditional holograms are created by the modulation of light phases to produce the illusion of depth. These holograms are facilitated by the principle of interference. In our conventional holographic device, we will have a reference beam that is concentrated on a recording surface and another beam of light concentrated on an object. When the two beams cross each other, an interference pattern in created. But, in order to produce these illusions, the holograms must be as thick as the optical wavelengths to create enough phase shifts.
Gu’s research team was able to find a way to overcome the traditional limitations of thickness by using metamaterials to create a thin film of antimony telluride to create optical resonant cavities. These cavities cause light that enters to reflect enough times to produce waves in different phases, which creates a 3D illusion.
What makes the research even more interesting is that these holograms aren’t like your traditional freestanding holograms in that there isn’t actually any distinct light being projected above the screen. The new hologram works by producing flat holograms that trick your eyes but in a much higher resolution, making the images appear to be larger and more detailed.
The researchers have stated that the material can be easily fabricated with 3D printing and is scalable. The team realizes that there are quite a few obstacles to overcome, but is looking towards researching a thin film that can be placed over a display device that would enable hologram projection, as well as making the projection surface flexible for a variety of applications.
Stretchy Metamaterials Allow for Shape-Changing Holograms
Almost all of our holograms are just recordings of a single picture, though some are capable of switching between a few images. However, that could be changing very soon. In another recent hologram research publication, researchers have been able to create holographic images that are capable of changing form, a potentially groundbreaking discovery that could lead to further research and development of moving 3D holograms.
Representation of the shape-changing hologram system. Screenshot courtesy of the American Chemical Society.
A team of scientists, led by Ritesh Agarwal from the University of Pennsylvania, have created a hologram that produces different images when stretched. The new lens was built upon from research last year that produced a metasurface lens from a stretchy material composed of polydimethylsiloxane that had been embedded with gold nanorods. This research showed that by stretching the metamaterial surface from the corners, that they could effectively change the focal length of the lens, allowing magnification.
Using the prior research, Agarwal thought it possible to create a hologram from the same material he had used to create the lens. Using various simulations and computer programs, the researchers were able to create hologram designs. The team precisely aligned gold nanorods onto a silicon wafer in specific patterns that would produce different images when stretched, then layered it in polydimethylsiloxane.
There have already been 3D polarized holograms that could produce up to two different images. Unfortunately, this technology can only house two images and requires sizeable optical equipment to make adjustments. Meanwhile, the new stretch hologram is sized on a micrometer scale, is capable of storing three holographic images (which increases drastically with device size), and has the ability to encode data.
The group has been continuing their research, producing multicolor images, as well as receiving funding to research a stretch hologram that can shift in response to electronic signals. It is also possible to create a much larger version of their stretchy hologram that could contain thousands of different images which, in turn, opens the door to creating animated holograms.
The original research paper can be found here.
Featured image used courtesy of RMIT University.