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April 7, 2013

Better (Rewriteable) Holograms

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Live, 3-D holographic movies or televisions are now a big step closer. As this ScienCentral News video explains, researchers are developing them using a new material that makes holograms rewritable.

Interviewees: Paul Barefoot, Holophile, Inc and Nasser Peyghambarian, University of Arizona
Length: 1 min 41 sec
Produced by Joyce Gramza
Edited by Chris Bergendorff

Copyright © ScienCentral, Inc., with additional footage courtesy University of Arizona

3-D TV?

"Ever since Princess Leia appeared out of the chrome dome of R2D2, people have sort of wanted holography to be that way," says Paul Barefoot, who runs a firm called Holophile, Inc. that specializes in holographic displays for museum exhibits, trade shows and advertisements.

That famous scene from the movie Star Wars is still science fiction, optics researcher Nasser Peyghambarian says, "but now we are very close to doing that in reality."

Peyghambarian and his team at the University of Arizona have made holography rewriteable, overcoming a longtime limitation.

Just like in conventional holography, they use lasers to record the 3-D images onto a piece of film. But unlike current holograms, their images are not permanent.

That's because current holograms use a type of plastic film called a photopolymer, and writing on the film permanently changes its structure, so it's "like a printed picture, except of course it's a 3-dimensional printed picture," Peyghambarian says. "In our case, the photopolymer is replaced by another type of plastic, which we call a photorefractive polymer."

Photorefractive polymers have a sort of memory because they can hold a certain distribution of charges. So to write an image on a photorefractive film, "all we do is change the distribution of the charge carriers rather than chemically change the whole material," he says. "And when we would like to erase it, we basically illuminate the whole area so that distribution is now completely even in the whole material."

"This plastic has the capability of being able to record the image very fast, in a matter of milliseconds," explains Payghambarian. "It has a persistence of a few hours-- meaning the image stays there for a few hours-- and it can be erased in a matter of less than a minute. And then a new image could be put in there, which is very different than what has been done before."

Peyghambarian, optics researcher Savas Tay, and their colleagues worked with materials scientists at the American subsidiary of Japanese company Nitto Denko to develop the updatable holography films. They published their research in the journal Nature.

The researchers say they'll soon be able to make these holograms bigger and more colorful. Their first demonstration used four-inch square films, but "we are going toward one-foot by one-foot and hopefully in the next few years we would be going the size of a human," says Peyghambarian. "Also, at the present time, it's a monochrome display for us-- just one color-- but we are working on three-color displays, so I'm expecting that in the next few years we should have full-color 3-D display available."

Much harder will be making them fast enough for movies or 3-D TV.

"Right now it takes us about two to three minutes" to erase and write a new image," Peyghambarian says. So "it wouldn't be usable for applications like 3-D video and 3-D cinema. Those you need much mucher faster rates of refreshing, so at this time we only focus on applications that would not require more than a few minutes of updating. So, 3-D video, 3-D movies-- they would be the next generation.

He says the first application may be in medical imaging, upgrading the current 2-D outputs with a third dimension. "We can actually update that information every few minutes. So, and using the same information that they already have through the MRI or CAT scan."

Another application he sees is military. "Commanders could sit around a table and manage the battle stage by looking at a three-dimensional view of the battle stage and update it very regularly."

And, of course, there's advertising. "These displays are pretty much attention grabbers-- people go toward them," he says. Stores or trade show exhibits "could change the product every few minutes… they could have an array of products that could be on display," Peyghambarian says.

Barefoot agrees that there's nothing like holograms for catching people's eyes. "The thing about holography is that it records things the way they really are. It's sort of like what photography should have been doing all along. It records the depth, and the dimension of an object or a scene so that you really think that you're looking at it."

As for those projected 3-D videos that people often think of as holograms, Barefoot explains that's a common mistake. "Anything that's 3D people have started calling it holography," he says. "There are many two-dimensional effects http://www.musion.co.uk/Al_Gore_Live_Earth_Tokyo.html -- projecting video onto glass or to film so that it gives the illusion of a three-dimensional image in space, when in fact it is not. Holography is the only one that can do that. "

Barefoot now thinks holography may finally live up to its potential. "People think that if it's in the movies, it's in real life, and that's not the case. Of course, that's where we'd like holography to be at one point, and this new dynamic hologram technology might lead us there.

"I never really thought holography could lead us into three-dimensional TV… because it is film based," says Barefoot. "This sort of starts the game all over again. It's pretty exciting."

Indeed, Peyghambarian says there are likely many applications the researchers haven't even begun to imagine. "It's an enabling technology, and those enabling technologies may have many applications," he says. "I think it has the potential of a very, very large market."

This research was published in Nature, February 7, 2008, and funded by the US Air Force Office of Scientific Research and the Arizona TRIF Photonics programme.

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