By Patricia Daukantas

The weather outside the Baltimore (U.S.A.) Convention Center has been varying wildly, from warm and summery to cool and rainy. Indoors, however, the atmosphere of the CLEO:2011 conference was steadily abuzz with exciting applications of the latest photonics technologies.

Ultraviolet LEDs Can Disinfect Water

Although CLEO is primarily a laser conference, some tracks focused on other photonics technologies, such as photovoltaics and quantum computing. Following a joint symposium on semiconductor ultraviolet (UV) lasers and LEDs, a session reviewed several practical applications of UV LEDs.

One task for which these devices are particularly suited is the removal of harmful germs and other contaminants from drinking water. Gordon Knight, a research manager at Trojan Technologies (Canada), explained that UV light penetrates the cell membranes of bacteria, viruses and protozoa and permanently alters their DNA so the critters can’t reproduce and infect humans. UV rays can also break down organic contaminant molecules, as long as the molecular absorption spectrum matches the output of the UV sources.

Water treatment specialists are primarily interested in the UV-C spectrum (200 to 280 nm), in which the peak absorption spectrum of germ DNA falls, Knight said. The industry’s workhorse has been the low-pressure mercury arc lamp, which has a strong emission peak at 254 nm. However, solid-state UV sources could be more energy-efficient and could maintain their steady output for five times longer than the mercury lamps.

Although some technical challenges remain in the development of UV-C LEDs--namely, cost and the need to boost individual chip output above 5 mW--Knight is confident that these sources will provide efficient instant-on operation for future water treatment devices, both in municipal plants and perhaps even in household-sized systems.

IARPA: An Opportunity, Not a Misspelling

You’ve heard of DARPA, but what about IARPA? The Intelligence Advanced Research Projects Agency, a new branch of the U.S. government’s spy agencies, recently started searching for “high-risk, high-payoff” research programs to boost America’s intelligence-gathering efforts.

According to IARPA official Michael C. King, the agency is especially interested in significant advances in techniques to gather biometric data from distant, moving human subjects. Successful proposals require not just a good idea, but also a capable leader to guide the research project. One U.S. team followed King’s talk with a discussion of their own technique for so-called “standoff biometric identification” of people. According to Brian C. Redman of Lockheed Martin (U.S.A.), Fourier transform profilometry involves bouncing fringes from an 808-nm laser off the subject, capturing it and its two-dimensional fast Fourier transform, then doing an inverse transform and merging it with the original data. The laser pulses are eye-safe and, with a duration of 100 microseconds, short enough to freeze motion at a brisk walking speed of 1.5 m/s. The near-infrared light can even “see” through most sunglasses, Redman said.

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