Magazine article National Defense

The Promise of the World's Smallest Lasers

Magazine article National Defense

The Promise of the World's Smallest Lasers

Article excerpt

About the thickness of a hair and the length of a few millimeters, quantum cascade lasers long have been a laboratory curiosity that only scientists could understand and operate. But recent advances in power efficiency, design and high temperature functionality have pushed this class of semiconductor lasers closer to real-world utility. One day they may provide the military with directional infrared countermeasures, target illumination, chemical warfare sensing and search-and-rescue capabilities, technologists say.

Quantum cascade lasers, as the name infers, employ quantum mechanics principles to convert electrical power into optical energy. Though these devices are fabricated in the same way as their traditional diode counterparts, with thousands of thin layers of materials, quantum cascade lasers produce energy in a different way.

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Semiconductor lasers typically require electrons and "holes" to generate light energy. Quantum cascade lasers need only the electrons, which gain atom-like properties when confined into very narrow spaces.

Atoms have specific energy levels to which they can be excited. When they relax, they "fall" to a lower level and emit a photon. Electrons in the laser act the same way. Lining up multiple energy levels in a descending "staircase" causes electrons to cascade continuously and produce a photon at every step.

The material composition in a traditional semiconductor laser determines the energy wavelength that is produced. For example, a carbon dioxide laser emits light at approximately 10.6 microns.

In quantum cascade lasers, the wavelength is dictated not by material but by the size of the energy level positions, or "belts." Technologists can control the wavelength by increasing or decreasing the size of the belts.

"Now I don't have to go to exotic materials," says Kumar Patel, founder and president of Pranalytica Inc. based in Santa Monica, Calif.

Most semiconductor lasers must be cryogenically cooled in order to function. Even when cooled, they generate only milliwatts of power, which renders them inefficient for practical use. "That's why this field remained fallow for many, many years," says Patel.

The high-power quantum cascade lasers produced by Pranalytica can generate watts of power and run on continuous operation at room temperature. "They're different from any other semiconductor laser that ever existed before," Patel says. …

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