A new class of transparent projection screens could bring vehicle and aircraft navigation, advertising – even eyeglasses – to a whole new level. A team from MIT, the Harvard departments of Physics and the U.S. Army Edgewood Chemical Biological Center has developed an inexpensive transparent projector screen using a resonant nanoparticle scattering technique. Nanoparticles that interact with a single color (in this case, blue) are incorporated into a transparent material. The result is a material that lets most of the ambient light go through and, therefore, appears transparent. Courtesy of Chia Wei Hsu. Transparent projector screens offer a wide viewing angle and can be scaled to large sizes, researchers say. They could be used in many ways, including showing navigation on car windshields and aircraft cockpit windows. Projecting information and images on glass windows and storefronts could enhance advertising practices. “Think of all the surfaces covered by windows,” said Marin Soljacic, a physics professor at MIT and leader of the team. “It is a lot of space that is not fully used. When I stroll downtown and look at the glass of skyscrapers at night, or at the subway windows, I imagine all that we can project on them.” The investigators’ technique also could lead to new developments and applications, such as flexible and scrollable displays, 3-D transparent screens, and peel-and-stick projection foils. On a white projector screen, all colors of the ambient light interact with it and are reflected. This is not possible with regular clear glass, as the ambient light and all colors simply pass through it. A sample transparent projection screen (left) and a regular piece of glass (right). A laser projector projects a blue MIT logo onto the transparent screen and the glass, which shows up clearly on the transparent screen but not on the regular glass. Courtesy of Chia Wei Hsu and Bo Zhen. The new technique uses nanoparticles, which can be tailored to interact with a single color and allow it to interact and resonate with transparent material. Incorporating such color-selective nanoparticles into transparent material lets most of the ambient light go through and, therefore, appears transparent, the team says. A high-resolution image can then be emitted by using a laser projector to send a light beam of the specific color that is scattered by the embedded nanoparticles. As a proof of concept, the team developed a screen that interacts preferentially with blue light. “The apparent color and brightness seem to be those of regular glass,” said MIT graduate student Bo Zhen, a member of the team. "The show begins when we project blue light.” In the future, the researchers anticipate that a full-color display could be implemented by embedding three types of nanoparticles, each scattering selectively red, green and blue. Alternatively, they could design a single nanoparticle with multiple resonances. The research, funded by the U.S. Army Research Office’s Institute for Soldier Nanotechnologies at MIT and by the National Science Foundation, is published in Nature Communications. For more information, visit web.mit.edu.