T-Rays Advance Toward Airport Screening

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Hu's lasers are a "key component" of a terahertz security device that Sandia National Laboratory is developing, says Sandia principal investigator Mike Wanke. The three-year project at the lab, now in its second year, aims to integrate a laser source and a detector into the same device. That eliminates complex optical setups and improves detector sensitivity by orders of magnitude, Wanke says. He envisions a module that can be used to make compact, commercially viable t-ray systems for use in airports. "We're trying to make this so it's a turnkey, drop-into-place system," he says. He adds that once Sandia has a successful prototype, businesses can tackle the challenge of product development.

The lasers need to reach lower frequencies to do a better job of penetrating material--the lower, the better, says Hu. But lower frequencies mean smaller quantum wells, which are harder to build accurately. Hu won't predict when commercial systems could be available.

But Xi-Cheng Zhang, director of Rensselaer Polytechnic Institute's Center for Terahertz Research says Hu "always breaks the record he sets for himself." Zhang says that either improvements in the engineering or use of different semiconductor materials is likely to make even better quantum cascade lasers. He expects that most of the problems will be solved in a year or two. One such problem is that the lasers operate at cryogenic temperatures and require bulky cooling equipment; Hu holds the record for highest operating temperature. After such problems are solved, market forces rather than technical issues will determine how long it takes for a commercial scanner to show up in an airport, Zhang says.

Zhang founded a company, Zomega Terahertz that makes a laptop-size T-ray detector that can be attached to a flying drone for remote detection of chemical and biological substances. While the trillionths of a watt produced by the infrared laser in the device is fine for spectroscopic analysis of air samples, it's not adequate for imaging, and the laser technology is unlikely to improve enough to be used in airport security, Zhang says. He believes that quantum cascade lasers are the future of T-ray detection systems: "They will be the final winner in the market."