Smalley’s team has taken a different approach — using a technique known as volumetric display — to create moving 3D images that viewers can see from any angle. Some physicists say that the technology comes closer than any other to recreating the 3D projection of Princess Leia calling for help in the 1977 film Star Wars. “This is doing something that a hologram can never do — giving you an all-round view, a Princess Leia-style display — because it’s not a hologram,” says Miles Padgett, an optical physicist at the University of Glasgow, UK.
They use forces conveyed by a set of near-invisible laser beams to trap a single particle — of a plant fiber called cellulose — and heat it unevenly. That allows researchers to push and pull the cellulose around. A second set of lasers projects visible light — red, green and blue — onto the particle, illuminating it as it moves through space. Humans cannot discern images at rates faster than around 10 per second, so if the particle is moved fast enough, its trajectory appears as a solid line — like a sparkler moving in the dark. And if the image changes quickly enough, it seems to move. The display can be overlaid on real objects and viewers can walk around it in real space.
The images created so far are tiny — just millimetres across. And only simple line drawings can be created at the speeds needed to fashion moving images. The team managed to depict a moving spiral line drawing and the static outline of a butterfly.
The technique needs substantial development but is a simple design with huge potential for improvement, says William Wilson, a researcher in nanotechnology at Harvard University in Cambridge, Massachusetts.
A glowing image resembling a futuristic hologram floats in mid-air. This is a 3D volumetric display. Using a tiny particle suspended in laser light, researchers have been able to create high resolution, color images that take up real 3D space. Developing this technology could lead to the kind of complex, interactive displays common in science fiction.
Free-space volumetric displays, or displays that create luminous image points in space, are the technology that most closely resembles the three-dimensional displays of popular fiction1. Such displays are capable of producing images in ‘thin air’ that are visible from almost any direction and are not subject to clipping. Clipping restricts the utility of all three-dimensional displays that modulate light at a two-dimensional surface with an edge boundary; these include holographic displays, nanophotonic arrays, plasmonic displays, lenticular or lenslet displays and all technologies in which the light scattering surface and the image point are physically separate. Here we present a free-space volumetric display based on photophoretic optical trapping2 that produces full-colour graphics in free space with ten-micrometre image points using persistence of vision. This display works by first isolating a cellulose particle in a photophoretic trap created by spherical and astigmatic aberrations. The trap and particle are then scanned through a display volume while being illuminated with red, green and blue light. The result is a three-dimensional image in free space with a large colour gamut, fine detail and low apparent speckle. This platform, named the Optical Trap Display, is capable of producing image geometries that are currently unobtainable with holographic and light-field technologies, such as long-throw projections, tall sandtables and ‘wrap-around’ displays.