Holograms Go Futuristic

You're walking down the street when you catch sight of a billboard ad. At first glance you see a woman clutching a can of Coke. Wait! Is the woman actually plastered on the billboard? She looks so real she could leap out of the ad at you. You watch her take a sip of Coke. Now, she's offering it to you! Hallucination??? No--hologram! Two British holographers are working to turn holograms into eye-boggling, full-color, animated billboards within two or three years.

Scientists now have taken their own bird's-eye view at holograms for a slew of new uses--from images on credit cards and CD-ROMs to thwart counterfeiters, to medical image scans that recreate images of the human brain. A hologram is like a photograph, only infinitely more realistic--it's 3-D, or three-dimensional. For instance, a fiat, two-dimensional photo records light reflecting off an apple from one angle--the front of the fruit. But a hologram captures light bouncing off the apple from every angle and direction, just the way you see the apple in real life (see "Making A Hologram," below).

If you've ever watched 3-D flicks, you may think, "Ha! I've seen lots of holograms." Not so. Three-dimensional movies or photos are actually made with two identical images spaced a few centimeters apart. Special 3-D glasses combine the images to trick your eyes into thinking they're seeing 3-D.

You probably have seen holograms on stickers, watches, key chains, and even swim goggles. But holograms aren't just zany high-tech art. For a close-up look at two futuristic kinds of holograms, read on.

Conventional holograms are made using laser light. But researchers at the Massachusetts Institute of Technology (MIT) have developed a novel approach: They create electroholograms--holograms made with computers, not lasers. "You just compute what the laser would do," says researcher Wendy Plesniak at MIT's Media Lab. Electroholograms can create 3-D images of something that doesn't exist at all--like a design for a 21st-century car.

Car designers often use computer-aided design (CAD) to create a 3-D diagram of a car. But a computer screen can produce only flat images of the CAD Car.

TOTAL VIEW

To see the car in 3-D, Honda, a Japanese company, turns to Media Lab to create an electrohologram of its design. This helps car designers view futuristic models from all directions--without ever having to build the car!

Programmers actually use CAD data to create the electrohologram. The computer uses math equations to simulate the action of a laser beam. The imaginary beam hits each point on the two-dimensional car design. Then, the computer calculates the interaction between the waves from the object beam and the waves from the reference beam. Result: a digital representation of the interference pattern.

CRYSTAL CLEAR

But this alone won't create a visible holographic image. Light needs to interact with the two-dimensional interference pattern in the computer to display the hologram. Enter: a crystal.

The hologram has to be displayed and illuminated outside the computer so viewers can see it in 3-D. To do this, an electronic device converts the interference pattern created by the computer--currently in digital code--into a radio signal with low and high frequencies. The varying radio frequencies can change a crystal's atomic structure. (Light waves just pass through the crystal.)

The radio signal enters a clear crystal and "carves out" the hologram inside it. Depending on its frequency, the radio signal makes some parts of the crystal more dense and others less dense, Plesniak explains. Shining a real laser beam through the crystal projects a freestanding, holographic image of the car.

Media Lab is now testing a robotic device to let viewers actually interact with the hologram. "Car designers would be able to go in and manipulate the 3-D shape that they're seeing--to make a curve a little more curvy," says Plesniak. The device would let viewers reach into the hologram, touch it, and change its shape!

Science--or magic???

Suppose doctors want to examine a three-dimensional image of the human brain. Such an image would make it easier to view a tumor and determine the best way to remove it--before cutting open a human skull. One solution: Make a hologram of the brain.

Voxel, a company in Laguna Hills, California, creates holograms out of a patient's CT (computer tomography) or MRI (magnetic resonance imaging) scans. CT scans are high-resolution X rays that "photograph" cross-sectional slices of bones, as well as blood vessels and soft tissue, like the brain. MRI scans are similar but use magnetic fields to peer at soft tissue in the body. Both scans provide very detailed pictures of a person's anatomy, but only as flat images. That's where holograms come in.

BIG BREAKTHROUGH

Recently hailed by Life magazine as one of the medical breakthroughs for the 21st century, Voxel's medical holograms give doctors a 3-D view of the human body. A hologram of a CT or MRI scan would allow brain surgeons, for example, to measure the exact size, depth, and location of a tumor.