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It's one of the most iconic scenes in all of science fiction: In the original Star Wars, the droid R2-D2 projects a 3-D image onto a tabletop. Princess Leia, projected as a tiny hologram, desperately asks the semi-retired Jedi master Ben Kenobi for assistance: "Help me, Obi-Wan Kenobi. You're my only hope."
Still brings the chills, doesn't it? The free-standing 3-D hologram has been a staple of science fiction for decades. But like the phaser and the flying car, it's one of those sci-fi dreams that has yet to become reality.
We're getting awfully close, though. Earlier this summer, researchers at the University of Rochester unveiled the latest projection system to approximate Princess Leia's immortal plea. Dubbed the Illumyn 3-D Display, the system uses laser projection to generate actual 3-D holograms in midair — no projection surface, no virtual reality goggles, no 3-D glasses, no augmented reality tricks.
There is a catch, however: Holograms projected by the Illumyn system are contained within a glass sphere filled with heated Cesium vapor, an elemental metal that's particularly good at emitting light. The Illumyn system works by crossing two laser beams — invisible to the human eye — at a specific point within the sphere. When the crossed beams hit the cesium vapor, various atomic-scale shenanigans produce a sky-blue light that is emitted outward in all directions.
The crossed beams only produce a single point of light, but by moving the laser coordinates around at incredible speed, the Illumyn sphere can essentially draw 3-D objects in thin air — well, thin cesium vapors. The image never actually exists at any one time, but the system fires up each dot so fast that the human eye sees the programmed image.
The process is actually a kind of high-tech update on the old cathode-ray tube television, says Curtis Broadbent, research associate in the Department of Physics and Astronomy at the University of Rochester and co-developer of the Illumyn system.
"CRT televisions used a raster-scan technology," Broadbent says. "The electron gun sends a stream of electrons to the fluorescent screen and the beam of electrons are deflected to sequentially hit every pixel on the fluorescent screen. Though we perceive an entire image on the screen, in actuality, only one pixel is illuminated at any time."
The Illumyn's geometric line drawings might look familiar to veterans of the 1980s first-wave video game craze, too.
"Actually, our technique is more akin to vector graphics displays commonly used in old video games like Atari's Asteroids," Broadbent says. "In vector graphics displays, only 'on' pixels are drawn; 'off' pixels are skipped completely. This reduces the number of pixels which must be visited by the electron gun."
For now, basic line drawings are as good as it gets with the Illumyn system, technically known as a laser-induced-fluorescence volumetric display.
Creating a true three-dimensional image in midair — one that can be seen from any angle — requires colossal amounts of information processed at, quite literally, the speed of light. Current computing systems just aren't up to it.
It's not from lack of effort, though. Earlier this year, a team of Australian and Chinese scientists showcased a new nanoscale hologram technology that can store massive amounts of visual information in tiny holographic images as small as 25 nanometers. For comparison, consider that a sheet of paper is about 100,000 nanometers thick.
These images are not free-standing holograms like the Illumyn produces, but rather virtual holograms that trick the eye into seeing three-dimensional images on a two-dimensional surface — like that symbol on your credit card. Pile up enough of these nanoscale fractal holograms, and your eyes will think they're seeing an impossibly detailed 3-D image projected up from a 2-D display surface, such as a phone or tablet screen.
In press materials announcing the new technology, researcher Lei Wang of the Australian National University admits to a pop-culture inspiration for the project.
"As a child, I learned about the concept of holographic imaging from the Star Wars movies," says Wang, a doctoral student with ANU's Research School of Physics and Engineering. "It's really cool to be working on an invention that uses the principles of holography depicted in those movies."
Keep it real
As impressive as the technology is, Wang's nanotech holograms are still fundamentally the same as optical illusions or virtual reality holograms. They're not really there at all; we just think they're there. For the full-on Princess Leia hologram — distinct moving images made of light and projected onto thin air — we're likely going to have to wait for a long while, Broadbent says.
Or maybe not.
"Well, there is a way to generate real-space 3-D holograms in thin air, but it's quite dangerous," Broadbent says. "The only way to make 'thin air' actually create light is to generate a small plasma field by ionizing the air locally."
Outdoorsy types may be familiar with this phenomenon already — it's called lightning. On a smaller scale, we've been ionizing air in laboratories since the 19th century — think Nikola Tesla — and it's an inherently dangerous business.
But at least one company is pursuing this line of development as a commercial endeavor. A few years back, the Japanese company Aerial Burton hosted a public display of its laser-plasma emission technology, generating quite a few viral videos like the one below. ("Note the safety barriers," Broadbent says.)
Click around online, and you can find other clever approximations of freestanding hologram technology involving acoustic levitation, air columns, pyramids and Victorian-era stage magic tricks. Those famous virtual performances by Michael Jackson and Tupac, for instance, are actually based on a 19th-century stage illusion known as Pepper's Ghost.
But when it comes to genuine holograms — freestanding three-dimensional images made of nothing but light — we're still waiting on the real deal. Help us, Obi-Wan. You're our only hope.