Small, high-powered laser zaps threats

Highly sensitive, semiconductor-based lasers, called the Quantum Cascade Laser (QCL), may soon provide infrared military and civilian countermeasures to protect aircraft from heat-seeking missiles and be built into highly sensitive chemical detectors that can rapidly detect trace explosives and other toxins at a safe distance for emergency personnel.

Researchers at Northwestern University today said Quantum Cascade Laser systems will be easily portable by a soldier, aircraft or unmanned vehicle, while being lightweight, compact and power efficient.

In addition, such systems also would need to be widely deployable and available to all soldiers, airplanes and public facilities, which requires a low production and operating cost.

While several types of lasers exist today that can emit at the desired infrared wavelengths, none of these lasers meet the above requirements because they are either too expensive, not mass-producible, too fragile or require power-hungry and inefficient cryogenic refrigeration, researchers said in a statement.

The Center for Quantum Devices (CQD) at Northwestern University, demonstrated individual lasers, 300 of which can easily fit on a penny, emitting at wavelengths of 4.5 microns, capable of producing over 700 milli-Watts of continuous output power at room temperature and more than one Watt of output power at lower temperatures.

Furthermore, these lasers are extremely efficient in converting electricity to light, having a 10% wall-plug efficiency at room temperature and more than 18% wall-plug efficiency at lower temperatures.

This represents a factor of two increase in laser performance compared to existing laser and is far superior to any competing laser technology at this wavelength, the researchers claimBell Laboratories says aquantum-cascade laser is a sliver of semiconductor material about the size of a tick.

Inside, electrons are constrained within layers of gallium and aluminum compounds, called quantum wells are nanometers thick - much smaller than the thickness of a hair.

In such a tight space, electrons take on properties explained by quantum physics.

Specifically, they jump from one energy level to another, rather than moving smoothly between levels and tunnel from one layer to the next going "through" rather than "over" energy barriers separating the wells.

When the electrons jump, they emit photons of light.Lasers operating in the 3-5 and 8-12 µm wavelength ranges can make use of high atmospheric transmission for long distance applications such as remote chemical sensing and laser radar.

Because of the long wavelengths these lasers are much less sensitive to bad weather and smoky conditions, researchers said.

Further, room temperature operation allows a more reliable transmitter in a smaller package. By combining high power, long wavelength emission, and room temperature operation into one package, the QCL becomes a clear candidate for realizing a compact, reliable, wireless free-space communications, useful for high-speed, free-space optical communication links which could prove useful for providing high-speed internet access in built up areas as expensive optical fiber installation can be avoided.

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