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Real-Time Holograms Beam Closer to Reality

3 November 2010 2:00 pm
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It's not quite the flickering blue projection of Princess Leia begging, "Help me, Obi-Wan Kenobi, you're my only hope!" from the classic sci-fi movie Star Wars, but holographic projection has just beamed a bit closer to reality. Researchers in Arizona have devised a novel plastic film that can be used to generate holographic 3D images sent electronically from one location to another. The new telepresence setup doesn't work yet at full video speed—it can update images only every 2 seconds—but the technology opens the door for everything from holographic surgery to movies that literally surround the viewer.

Holograms are more than just fancy photographs. Shift your head to the side while looking at a photo, and the image doesn't change. Do that with a hologram, and instead of staring at the front of an image of, say, a fighter jet, you're looking at the side (see video). Lasers are the key: When recording a hologram, one beam of laser light illuminates the target. This light is combined with light from a second "reference" beam, creating an interference pattern akin to the one seen when two sets of ripples overlap on a pond. When this light strikes a photographic plate, the interference pattern is recorded. Later, shining a light back on the photographic plate causes light to diffract off the interference pattern, reconstructing the 3D image.

Rapid fire. A laser fires a series of brief light pulses to quickly write and update the image of an F-4 Phantom Jet.
Credit: Nature

Researchers have been creating holograms for decades—yet they've struggled to make them practical. Among the biggest challenges: the traditional crystalline photographic materials used to capture holographic images are expensive and have trouble covering large areas. Two years ago, Nasser Peyghambarian, an optics researcher at the University of Arizona, Tucson, and his colleagues overcame these limitations when they devised a polymer-based holographic film that was potentially far cheaper than the conventional materials and also easier to grow in large areas. Moreover, the researchers were able to write new images every 4 minutes. But that was hardly a moving picture. So Peyghambarian and his colleagues continued to search for improvements.

In their new paper, published online today in Nature, Peyghambarian and colleagues at Arizona and the Nitto Denko Technical Corp. in Oceanside, California, describe a holographic display that can depict a scene in another location and update the image nearly in real time. The setup starts with 16 cameras arranged in a semicircle around a target. The cameras take simultaneous pictures of the target every second. The camera views are processed by a computer and sent via an Ethernet cable to the photographic recording site, which conceivably can be in the next room or half way around the globe. There, a laser setup receives the image data and shines a steady stream of pulses encoding the images as well as laser light from a reference beam at an improved polymer film, which in turn records the resulting interference pattern. A separate light is then shown from an angle on the other side of the polymer film, generating the hologram as it does so.

Among the advantages of the current setup, Peyghambarian says, is that images can be recorded on one side of the photographic film and viewed on the other. As a result, three people gathered around a table housing the holographic film wouldn't see the laser setup under the table. Rather, they would be able to see a holographic image of, say, a car, and, depending on where they were standing, either the hood, trunk, or doors.

That ability could lead to holographic movies that allow viewers to walk around the scene, for example. It could also bolster the budding field of telemedicine by allowing specialists from around the world to see a patient from all angles, offering their opinions to doctors on site.

"It certainly has got my attention," says Eric van Stryland, an optics expert at the University of Central Florida, Orlando. Stryland notes that Peyghambarian's team has already improved the speed at which his system can refresh images by about 100-fold, and it needs only another improvement by a factor of 10 to approach the 30-frames-per-second speed required for full motion video. "About another order of magnitude and they'll be there," he says. Peyghambarian says there are no physical showstoppers preventing his photorefractive polymers and lasers from reaching that goal, although he says that doing so will require the use of faster pulse lasers, among other things.

Light sabers—those might take a little more work.

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