A new technique uses ordinary white light instead of a laser to make three-dimensional color holograms that can be viewed at any angle, something that could prove useful in the next generation of 3-D displays, Japanese researchers report. Three-dimensional, true-color image of an apple generated using a new technique of making holograms that allows the image to be viewed using ordinary white light. (Images: ©Science/AAAS) The method differs from conventional techniques because it’s based on the activity of electrons on the surface of a metal film. Current approaches generally bounce laser light off an object and onto a photographic plate, which records information about the light waves’ phase and amplitude in the form of an “interference pattern.” Then, when light shines through the hologram, it interacts with the interference pattern in such a way that the image of the object appears, usually in a single color. Another type of hologram, the “rainbow hologram” commonly found on credit cards, appears in different colors under white light. But certain information about the image gets filtered out while making these holograms, and the color changes with viewing angle. Miyu Ozaki of RIKEN and the department of robotics and mechatronics at Tokyo Denki University and her colleagues now describe a method for making multicolored holograms, the colors of which stay the same when viewed from any angle, just like the original object. A surface plasmon hologram. Their technique is based on the diffraction of electronic excitations, called plasmons, propagating at the surface of a thin metal film. The researchers coat the metal film onto a light-sensitive photoresist material containing a hologram made with red, green and blue lasers. The photoresist hologram itself rests on a thin glass plate. The surface plasmons in the metal film are excited using white light oriented at a range of angles. The angle of the incoming light determines which plasmons are excited and diffracted by the hologram, reconstructing the light waves reaching the viewer’s eyes so that the 3-D image appears. Because it is relatively simple and scalable, this method may lend itself to real-world applications, in which viewers wouldn’t have to wear specialized glasses or sit at a particular angle to view the 3-D image, the researchers say. Their work appears in the April 8 issue of Science. For more information, visit: www.sciencemag.org