The efficiency of certain infrared lasers has been doubled, making them more useful for defense-based applications such as missile diversion and explosives or toxins detection.

Over the last year, researchers at the Center for Quantum Devices at the McCormick School of Engineering at Northwestern University, led by Manijeh Razeghi, the Walter P. Murphy Professor of Electrical Engineering and Computer Science, have improved infrared laser efficiency under DARPA’s Efficient Mid-wave Infrared Lasers (Emil) program by making changes in material quality, design and fabrication to advanced mid-infrared semiconductor lasers previously developed at the university.

The Emil program was created to develop high efficiency, compact semiconductor laser sources, particularly in the mid-infrared wavelength range (3 to 5 µm) with the aim of demonstrating both high power (~1 W) and high power efficiency (50 percent) from an individual laser at room temperature. In addition to representing a significant energy savings over current laser sources, the quantum cascade laser will be more compact than any other laser at this wavelength range and operating temperature, with an active volume that is smaller than a human hair, the researchers said.

As these types of lasers become more efficient, meaning they require less input power than similar lasers but produce the same output, they could be used in next-generation laser-based defense systems to fool incoming missiles or detect explosives or toxins in the atmosphere. They could also be used in commercial applications like trace chemical analysis, pollution monitoring, and free-space communication. But first the right laser sources must be found at the right wavelengths.

When the Emil program started in March 2007, the lasers used had power efficiencies on the order of five to 10 percent at room temperature. Over the past year, the Northwestern team has made gradual improvements, with the current record being a power efficiency of 22 percent at room temperature (25 °C). This means that for the same power output, two to four times less input power is required. When cooled, the power efficiency increases to 34 percent at 160 K (-113 °C), which is also a record for this type of device, the researchers said. Along with high efficiencies, high output powers have also been demonstrated, with multiwatt output powers up to room temperature.

Research and development work will continue on the project over the next two years. Once the laser is developed, it will be a strong candidate for mass production, like the shorter wavelength semiconductor lasers used in CD and DVD players, they said. Mass production will reduce the laser's cost and allow it to be used in commercial applications.

While the team's intermediate accomplishments were published in the March 10 issue of Applied Physics Letters, the work is not yet published.

For more information, visit: www.mccormick.northwestern.edu