Screening Device That Peeks Through Everything

The threat brought to airplanes by terrorism, but also old plagues - such as drug trafficking - made necessary the jump from science fiction to the reality of some of the most sophisticated screening devices.

That's what Sandia National Laboratories, a National Nuclear Security Administration (NNSA) laboratory, is designing.

The next generation of screening technology will track down explosives, drugs and toxic materials through clothing and packaging materials. The technique employs integrated miniaturized terahertz (portion of the electromagnetic spectrum that lies between microwaves and infrared) transmitter-receiver (transceiver). "The technology being developed in the Grand Challenge can be used to scan for items such as concealed weapons or materials, explosives, and weapons of mass destruction," says Mike Wanke, principal investigator.

"In addition, we believe it will find applications in advanced communication systems and high-resolution radars. However, the infrastructure needed to move the terahertz technology from the laboratory to the field is unavailable right now. We want to develop that infrastructure and invent the necessary technologies."

"The terahertz situation has begun to change dramatically (in the last 3 years), primarily due to the revolutionary development of terahertz quantum cascade lasers."

The technique is now possible due to the achieving devices smaller than a baseball, powered by a 9 volts battery: while these minilasers can output over 100 mW, previously the same amount of power required over 100 kg molecular gas lasers with volume cubic meters or free electron lasers as big as a building and weighing tons.

This was achieved by developing unique semiconductor crystals by epitaxy (a method of laying down layers of materials with atomic thicknesses onto substrates that can be used) for operating terahertz quantum cascade lasers.

The team is currently testing and exploring packaging requirements, and after three years, a working prototype reading distinctive molecular spectral "signatures" will be ready. "Most materials and chemicals have their own unique terahertz spectral signatures," Wanke says. "A terahertz transceiver system would be able to measure, for example, the signature of a gas and determine what it is."

"Atmospheric scientists and radio astronomers have spent years developing terahertz spectral signature databases to identify chemicals in nebula and planetary atmospheres," says Greg Hebner, program manager.

"Even though the current devices are washing machine-sized, they are located in a few observatories, and one is even flying on a satellite. To address specific national security problems, we are working on reducing the size, weight, and power requirement as well as expanding the existing spectral databases."

The team also sees other uses for the device, like tracking toxic materials in the air. This technology, combined with mass spectrometer-based systems, would improve false identifications. "This is an unexplored area and a lot of science can come out of it. We are just beginning to scratch the surface of what THz can do to improve national security", said Wanke.