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Writing with Light

A 12-inch LP records about an hour of music in tiny grooves in its plastic surface. A compact disk packs more information into a smaller area, but it, too, stores data only on its surface.

If information could be tucked inside the disk instead of just on its surface, researchers have hypothesized, a single CD could hold an entire encyclopedia's worth of information in the form of words, pictures, music or movies.

Now a team of UB scientists has built a system with just this potential. And the special materials they invented to create it are turning out to have a mind-boggling array of other uses-including helping scientists peer inside solid objects, and assisting doctors in fighting cancer.

The group is exploiting a new technology called photonics. Just as electronics uses electricity and electrons to record and transmit information, photonics uses light and its tiniest parcels, photons, to perform such tasks.

To capture photons, Professor Paras N. Prasad and his colleagues at UB's Photonics Research Laboratory have synthesized several unusual fluorescent dyes they call chromophores.

When an ordinary fluorescent substance-a material that glows after being bathed with light-absorbs photons, the photons lose a little of their energy before being emitted again as part of the fluorescent glow. The newly emitted photons therefore have less energy than the original ones.

In contrast, Prasad's dyes actually increase the energy of the photons they absorb, a property called upconversion. The dyes also strongly absorb certain wavelengths of infrared light, a category of radiation that includes microwaves and heat radiation. This turns out to be a critically important property because infrared radiation can penetrate solid substances in a way that visible light cannot.

The UB scientists blend their dyes with an inexpensive plastic, then use a laser beam tightly focused through a microscope to shine infrared light on specific spots. Using special computer programs, they can manipulate the beam to "write" data into the plastic.

"These new materials revolutionize data storage," says Prasad, "because they allow data to be stored in the depth of a disk, not just on its surface."

The data can be written in layers separated by only a few microns-or millionths of a meter.

"You would have to stack more than 1,000 conventional CDs one on top of the other in order to get the same amount of data that is in one cubic centimeter of one of these new materials," explains Prasad's colleague Jayant Bhawalkar, a UB research assistant professor.

The system can store digitally encoded information, such as words or music; it can also be used for analog data like photographs and movie footage.

To demonstrate the system's capabilities, the UB team has recorded several seconds of a Bugs Bunny cartoon in a cube of plastic that's only as wide as a human hair.

The research is the result of wide-ranging collaborations both inside and outside the university. Prasad's photonics group works with the university's Advanced Microscopy and Imaging Laboratories, as well as the Polymer Branch at the U.S. Air Force Wright Laboratory in Dayton, Ohio.

The new technology is attracting widespread interest because of its many potential applications.

For example, the new dyes can be used to help scientists see under the surface of solid objects without cutting them open. And airplane paint mixed with a chromophore-although it looks no different from ordinary paint-becomes transparent to infrared light, which allows technicians using a microscope modified for infrared to focus right through the surface of the paint to find flaws or places where it failed to bond with the metal underneath. Prasad says the same technique could someday help dentists inspect fillings without using a drill.

The Photonics Research Laboratory has also begun a collaboration with Roswell Park Cancer Institute, where researchers are finding that the new chromophore dyes can enhance an innovative cancer treatment called photodynamic therapy.

In photodynamic therapy, cancer patients are injected with a photosensitive drug that accumulates in their tumor. When the chemical is illuminated with laser light, it releases a highly toxic form of oxygen that proves deadly for the cancer cells.

Because this therapy currently works only with tumors that doctors can reach with a beam of light, photodynamic therapy is used today for cancers on the skin or in places like the esophagus that can be reached with a fiberoptic device.

Infrared light, however, is better than ordinary light at penetrating living tissue, so it can reach tumors that are much deeper in the body. Mixing the cancer-killing drug with one of Prasad's chromophores makes the drug respond to infrared light.

In animal tests, the UB team has demonstrated that the new treatment succeeded in destroying deep tumors without producing side effects. "Although these are preliminary studies," Prasad says, "they are very exciting."

Jessica Ancker is editor of Buffalo Physician, published quarterly by the UB School of Medicine and Biomedical Sciences.


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