The innovation could one day lead to 3-D holographic movies, enabling cinema-goers to feel they are "inside" a movie yet not have to wear cumbersome, headache-inducing spectacles with polarising or coloured lenses, the inventors hope.<\/p>\n
Other beneficiaries include military commanders, who could gain a three-dimensional picture of a battlefield, and surgeons performing complex micro-surgery inside a patient.<\/p>\n
In a paper released by the British journal Nature, Nasser Peyghambarian of the University of Arizona and colleagues reported how they recorded, displayed and updated images on a palm-sized screen measuring just 10 centimetres by 10 centimetres (four inches by four inches).<\/p>\n
Holograms are created by shining a laser on an object, whose image falls onto a photosensitive screen. At the same time, a second laser beam falls on the screen, creating an "interference pattern" — in essence, the condensed contours of the object, which are imbedded in the film.<\/p>\n
It takes a third laser, called the reading beam, to be directed onto the screen for the interference pattern to be resurrected. To a person in front of the screen, this creates an image in three dimensions that appears in mid-air behind the screen.<\/p>\n
These holograms are widely used in advertising, art and entertainment but the drawback is that their displays are static.<\/p>\n
The new technology, though, can store the image, erase it and update it, say the inventors.<\/p>\n
Although still at a prototype stage, it means that one day a 3-D motion picture is a clear possibility, they believe.<\/p>\n
The secret lies in films called photorefractive polymers which contain molecules of dye that respond to light and rotate and line up in response to an applied electrical field.<\/p>\n
On their small display, Peyghambarian's team were able to update the image in about three minutes and hold it there for up to three hours.<\/p>\n
Anyone hoping for a zappy "Star Wars"-style hologram that can be viewed from any point in the room would be disappointed, though.<\/p>\n
The parallax, or 3D effect, still can only be seen within a given angle by a person in front of the screen. Move too far to the right or left or up or down, and the effect is lost.<\/p>\n
Joseph Perry of the Georgia Institute of Technology in Atlanta, in a commentary published by Nature, said the innovation was extraordinarily promising, not least because the polymers were potentially cheap and easy to produce.<\/p>\n
It was only a matter of time before higher-powered lasers and more sensitive photorefractive polymers ushered in larger and faster 3-D displays, he predicted.<\/p>\n
"The technology still has some way to go to maturity but ultimately it's not just the cineastes who could benefit," he said.<\/p>\n
"Displays that provide realistic three-dimensional images with a wide angular viewing range might also be used in military or medical contexts, such as the simulation of field situations or the guidance of keyhole surgery."<\/p>\n
On the other hand, he noted, holographic displays could face fierce competition from flat-panel 3D screens and other rivals "that are coming on in leaps and bounds," he noted.<\/p>\n