Brent D. JohnsonIn support of the Defense Advanced Research Projects Agency's Semiconductor Ultraviolet Optical Sources program, researchers at Sandia National Laboratories in Albuquerque, N.M., have developed high-power AlGaInN-based LEDs that emit at ultraviolet wavelengths. The devices have potential applications in the development of handheld biological sensors and transmitters for non-line-of-sight covert communications, as well as in solid-state lighting, decontamination systems and polymer curing. Researchers at Sandia National Laboratories have demonstrated high-power LEDs that emit in the ultraviolet wavelength range for military and civilian applications. The new LEDs employ a flip-chip geometry and a thermally conductive submount to boost brightness and efficiency, respectively. One device produces 1.3 mW of 290-nm CW radiation under direct-current operation; the other produces 0.4 mW of 275-nm radiation. Biological sensors based on the emitters would employ laser-induced fluorescence to distinguish biological agents developed as weapons from naturally occurring organisms by the stimulated response of molecules of interest in samples that are collected and tested in real time. Such sensors would have small form factors and would require little maintenance and no consumables. Non-line-of-sight ultraviolet free-space interconnects would exploit the scattering of short wavelengths by aerosols and molecules to link sensors and communications systems by signals reflected from the atmosphere, insulating them from intercept, detection or jamming. Working at UV wavelengths carries two additional advantages: The high extinction coefficient of the atmosphere ensures that background noise is nearly zero, and it also thwarts eavesdropping or detection at a distance. Systems employing the technique would offer data rates of more than 1 Mb/s and operating ranges of 10 to 250 m. The Sandia researchers will continue to characterize the LEDs and have supplied samples to participants in the agency's program. The program includes research laboratories, universities and private photonics companies in the US.