The original Star Wars movie provided one of science fiction cinema’s most enduring images: A hologram version of Princess Leia, projected by droid R2-D2, requesting assistance for the Rebel Alliance: “Help me, Obi-Wan Kenobi — you’re my only hope.”
For a pre-CGI film made in 1977, it still holds up pretty well, doesn’t it? The concept of a freestanding 3D hologram wasn’t quite new to science fiction at that time, but Star Wars turned the concept into a trope. Such imagery is now practically de rigueur in sci-fi films, popping up in everything from Avatar to the Marvel Universe movies.
It’s been 44 years since Star Wars hit theaters, and since then we’ve developed the smartphone, orbital space stations, and maybe soon, cloned mammoths. Why don’t we have real-life Princess Leia holograms yet?
The happy answer is: We do! The more accurate answer is: We do! Kind of! But they’re pretty tiny. For now.
Daniel Smalley, director of the Electro-Holography Lab at Brigham Young University, is part of several research teams worldwide currently working on Leia-style holograms or, to use the emerging technical designation, free-space volumetric displays. These are 3D images (“volumetric displays”) that float in air (“free space”) and that can be seen from any angle without screens, glasses, or mirroring surfaces.
You could reach out to touch the image, but you would disrupt the delicate movement of the particles, essentially scattering the picture.
By contrast, many of the 3D holograms we encounter in the wild require a screen for viewing. Most “three-dimension” displays — commercial 3D televisions, for instance — create the illusion of depth on a two-dimensional viewing surface by manipulating the light reaching your eyes. Some “holograms” borrow from relatively ancient technology. For instance, those holographic music concerts featuring Buddy Holly or Tupac use optical illusion principles from a 19th-century stage-magic technique called Pepper’s Ghost, updated with newer theater technologies. From a distance, the images appear to have volume, but they are technically “virtual images” generated by a hidden screen surface, Smalley says.
“With a virtual image, you can’t stick your hand back there,” Smalley says. “Light is only appearing as if it originated from behind that plane.”
Smalley’s device — called an optical trap display — doesn’t require a 2D screen to produce a 3D image in space. It’s a “real image” as opposed to a virtual image. The optical trap display does this by bouncing light off tiny particles trapped in the air, then quickly moving them around using precisely calibrated lasers. The glowing particles make patterns in the air, “redrawn” more than 10 times per second.
“[Our system] actually puts little atoms out in regular air space, then scatters light off those atoms — there is no screen,” Smalley says. “Another way to think of it is to say we take the screen and chop it up in pieces, then scatter those pieces out into the image.”
The effect is similar to the way you can use a sparkler at night to create shapes in the air, but much faster and smaller. Your eye integrates the image using persistence of vision, producing a 3D figure floating in the air that you can see from every direction, Smalley says. Technically speaking, you could reach out to touch the image, but you would disrupt the delicate movement of the particles, essentially scattering the picture.
“We’re working on that, too,” Smalley says. “We’ve developed some automatic particle pickup techniques that would recreate the image so quickly you wouldn’t even see it happening.”
So what will it take for Star Wars holograms to become a reality in our galaxy? Smalley says that his team and other research groups are steadily improving techniques to create 3D volumetric images. Cross-pollination of ideas may be essential, since each individual approach has its limitations. Japanese scientists have been working on a system that uses superheated plasma particles to achieve the same sparkler effect — pretty cool, but potentially dangerous if scaled to larger sizes. Other approaches require fog emitters or cesium vapor contained in a glass globe, which limit the “free space” concept.
The limitation on Smalley’s system is the physical size of the hologram. For now, optical trap display images are pretty tiny — smaller than the size of your pinky fingernail. But he’s optimistic that the technology can scale up and have potential application in medical imaging, video games, or fomenting resistance against galactic empires.
“What we’re doing now is moving a single particle in a really complicated path,” Smalley says. “But in the future, what we’d like to do is take many particles and move them in a simple path. And we feel like that is the strategy that will get us to larger images.
“You know, Princess Leia images.”