Science fiction writers invented holovision as soon as they heard of laser holography in the mid 1960s, and holovision has remained a standard science-fiction prop ever since. Holographic 3D television was a perfectly logical extrapolation at the time, but just like flying cars and jet packs, it never really got off the ground. Until—perhaps—now.
Whatever happened to holography? You take it so much for granted that you don’t even notice it. Pull out a credit card and look at the shiny patch that makes rainbow patterns in the right light. That’s a hologram, although not a very good one. With luck, you’ve seen better ones, like “The Kiss,” in which a rainbow-colored woman named Pam Brazier leisurely blows a kiss as you move around it. But you didn’t see one in the first Star Wars flick; that projection of Princess Leia was a faked hologram. Nor was CNN’s “holographic reporter” a hologram, and the producers of Red Dwarf weren’t even trying with Rimmer. In fact, everything so far that claims to be holographic telepresence is a fake.
That’s the demonstration of holographic telepresence by University of Arizona scientists that made headlines in November, even though the fuzzy green images looked like they came from an out-of-whack camera. To understand why, let’s zip back in time nearly half a century and take a close look at what made those first laser holograms so special.
It started when Emmett Leith, a bright young engineer at the University of Michigan’s Willow Run Laboratory, figured out how he could use light to turn raw data from airborne radars into 3D maps of buildings and terrain on the ground. He used a bit of mathe-magic that turned a signal that varies in time into an image that varies in space. Leith and a younger engineer, Juris Upatnieks, then tried transforming images in other ways, and eventually the two came up with another trick—creating truly three-dimensional images with the then-new laser.
We’re not talking the fake 3D you saw in your ViewMaster toy, in comic books you read with red and green glasses, or at late-night horror movies. Leith and Upatnieks made holograms that projected light into space so you could look around it. They made a hologram of a toy train engine that hovered in space before your eyes like a ghostly red version of the toy engine itself.
Their trick was to reconstruct the wavefront of the light that would reach your eyes if you were looking at the object itself. To do it, they started by dividing a laser beam in half, using one half to illuminate the object, and bouncing the other half off a couple of mirrors to aim it at a photographic plate near the object. Laser light reflected from the object also illuminated the photographic plate. Because the laser light was coherent, with all the waves marching in phase like soldiers on parade, the two beams formed a special pattern when they exposed the photographic plate.
That plate, after being developed, stored all the information needed to create the ghostly image of the object. All you needed to do was shine a laser beam onto the plate, following the same path taken by the second half of the laser beam. The pattern recorded on the plate scattered the laser light to make a replica of the wavefront you would have seen from the object. The images Leith and Upatnieks reconstructed were red because they illuminated the plates with red laser beams. They also looked a bit grainy because of the nature of laser light.
Once you saw a hologram, it was a revelation. Researchers around the world started making their own holograms, then began making better ones. Steve Benton at Polaroid figured out how to make holograms that showed three dimensions when viewed in ordinary white light. You still needed a laser to record the hologram, but you didn’t need one to display a hologram. (Take another look at your credit card. That’s the kind of hologram it uses.) The image showed a rainbow of colors that changed as you moved your head, but that was cool, too. Then Lloyd Cross figured out a way to record a series of rainbow holograms and assemble them so the image seemed to move as you moved around it. (What he really did was to move a camera around a model, taking a picture at each step as the model moved, like Brazier blowing her kiss.) Those were fun, and attracted a lot of attention. Some appeared as extra heads of Logan in a scene in the movie Logan’s Run.
Holographic art was hot. Artist Salvador Dali exhibited holograms, and in 1976 the Museum of Holography opened in Manhattan’s SoHo district. But holovision was nowhere to be seen. Holographic images had to be projected by shining light through a hologram, but film holograms were fixed and unchanging. What holovision needed was a way to record a series of holograms, transmit them from the camera, and recreate the holograms to display the image—all at video rates of thirty frames a second. Nobody knew how do to any of that. Holograms had to be recorded with very fine resolution, producing tons of data, then replicated at a distance with all the data intact. That would require sheets of unobtainium to display the hologram. It looked hopeless.
Fast forward three decades, and we still don’t have the perfect rewritable holographic material. But now we have one that can be rewritten in seconds. It’s called “photorefractive,” and illuminating it with a bright laser pulse changes how it refracts other light. Illuminate it with fainter light, and it projects a holographic image.
The images aren’t permanent, but you don’t want permanent for holovision. You want the old frame to fade when you write the next one. At a November press conference, Nasser Peyghambarian, Chair of Photnics and Lasers and Professor of Optical Sciences at The University of Arizona, said he could write a new image in only two seconds. He borrowed Benton’s tricks so he could project holograms using green LEDs rather than needing a laser.
Two seconds a frame is a crawl by video standards, and his screen is only four inches square, the size of a smart phone, not a movie screen. Other optical compromises left the monochrome green image blurry. Nonetheless, it was good enough for Peyghambarian to boast he had demonstrated holographic telepresence. Other observers agree his images are a huge step forward. The image was “the size of Princess Leia,” Peyghambarian told the press conference, so holographic telepresence “is no longer science fiction, it is something you can do today.”
Can the holodeck be far behind? Should I put off buying that 3D TV?
It depends how you define “far.” Peyghambarian predicts that commercial applications are seven to ten years away, and they won’t be on the holodeck or in your living room. They are likely to be in fields like medical imaging or computer modeling, where real 3D images will be a big plus, but don’t have to be rewritten at full video rates. The images are likely to be monochrome, because full color is an unnecessary complication for those applications.
But developing the technology needed for those systems will pave the road to future home entertainment. When holographic television comes to your living room, it will give you true three-dimensional images that you can look around and see the back of the object, says Michael Bove of the MIT Media Laboratory. Because holograms are truly three dimensional, they shouldn’t give you the visual hangovers that come from watching too much conventional 3D. So spring for the 3D TV now; by the time holovision comes, you’ll be ready for a change.
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