Finding the Light

Professor’s tiny ultraviolet and infrared detectors could improve defense, health care

by Jeremy Craig

Unil Perera holds in his hand a tiny device with big potential. Resembling a computer chip and no larger than a fingernail, the black and gold object can detect invisible light waves emitted by cancerous tumors, or even the unique signatures of enemy firearms on the battlefield.

With the help of the National Science Foundation, Department of Defense, NASA, and other agencies, Perera, a professor of physics, and his colleagues have developed several types of these inexpensive devices to detect these unseen wavelengths.

“This technology can lead to low-cost, high-operating temperature detectors, which could go a long way to solve the problems facing us today and in the future,” Perera says.

In the electromagnetic spectrum, different waves of energy create different wavelengths. People can only see the visible spectrum of light, which ranges from red to violet. What Perera is studying is wavelengths beyond the visible spectrum — both infrared and ultraviolet waves.

Infrared waves have longer wavelengths than red light, while ultraviolet waves are shorter than violet light.

One of Perera’s infrared detectors uses a process called intrinsic absorption. In this process, infrared radiation is sent through a semiconductor. When exposed to ultraviolet light, a semiconductor atom can separate particles, negatively charged electrons and missing electrons, creating a current signaling the presence of that type of light.

More recently, Perera’s lab created a device that detects both ultraviolet and infrared radiation. These tiny detectors are based on quantum dots — semiconductors that are mere nanometers in size.

By detecting different wavelengths of light, scientists, doctors, soldiers and even manufacturers can use detectors to their advantage.

For example, with cancer, tumors generate a lot more heat than surrounding tissues due to increased blood use. Heat gives off infrared wavelengths, so doctors could use these devices to read this heat signature and detect the presence of an abnormality, Perera said.

On the battlefield, flashes from guns have unique ultraviolet and infrared signatures depending on the type of weapon. By using these detectors to identify the type of weapon, soldiers could determine whether to fall back in response to the weapons range.

On the homefront, Perera’s detectors could help replace X-rays for security screening, using infrared wavelengths that penetrate clothes and containers but are less harmful to humans. This imaging technology could even apply to quality control in factories.

“If you have a box of raisins, since these frequencies penetrate the box, you could even count the number of raisins inside,” Perera said.