Far-infrared or terahertz lasers can be extremely useful to all sorts of people and organizations. T-rays, able to penetrate a multitude of materials, can be used for such endeavors as medical imaging to detect tumors with no side effects, detecting cracks and irregularities in the space shuttles' seemingly super-delicate heat shield, or finding biological/chemical agents inside sealed packages.

One major drawback to date has been that a typical t-ray emitter must be cryogenically cooled to operate. The typical organic gas type THz laser is cooled to liquid helium temperature.

A newly developed, room-temperature t-ray laser by Harvard University may put the devices in the hands of "average" security, medical and safety engineers everywhere. The team, led by research associate Mikhail Belkin and the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering, Frederico Capasso -- with whom another group at Harvard recently showed their work in nanowire LEDs -- of Harvard's School of Engineering and Applied Sciences used a specially designed Quantum Cascade Laser (QCL) to produce the terahertz level beam.

To produce THz radiation from a mid-infrared laser device, the group designed a QCL that emits two frequencies of light concurrently. The THz radiation itself is created by difference-frequency generation inside the laser medium. Their emitter kicks out t-rays of a respectable 5THz at a few hundred nanowatts of power. Microwatts are achievable with commercially available thermoelectric coolers, says Belkin. "Further, there is the potential of increasing the terahertz output power to milliwatt levels by optimizing the semiconductor nanostructure of the active region and by improving the extraction efficiency of the terahertz radiation."

Not only is the Harvard t-ray laser operable at room-temperature, due to its construction process, it should lead to relatively inexpensive and mass-producible detection and imaging systems. Capasso explains, "Terahertz imaging and sensing is a very promising but relatively new technology that requires compact, portable and tunable sources to achieve widespread penetration. Our devices are an important first step in this direction. We believe our THz source has great development potential because the nanoscale material used was grown by Molecular Beam Epitaxy, a commercial and widely used thin film growth technique which 'spray paints' atoms on a surface one layer at a time."

The multi-university team's work, which includes Harvard, Texas A&M and the Institute of Quantum Electronics in Zurich, will be published in today's issue of Applied Physics Letters.