"Our aim with the Terahertz Microelectronics Transceiver Grand Challenge is to enable detection of hazardous, toxic materials by creating a compact, completely solid-state integrated terahertz transceiver," said Mike Wanke, principal investigator at Sandia National Laboratories, "instead of [the] bulky, cubic-meter-sized molecular-gas terahertz lasers, or the even larger free-electron lasers, required today."

Sandia National Laboratories is currently experimenting with air preconcentration techniques to enable the direct identification of toxic vapors by shining the terahertz transceiver into them and reading out their spectral signature with the device. Wanke believes that, by working in tandem with mass spectrometer-based systems, devices can also be crafted to produce very low false alarm rates in chemical-detection systems.

The enabling technology for the terahertz transceiver is the development of terahertz quantum cascade lasers by Sandia National Laboratories and others, including the Massachusetts Institute of Technology (MIT). Only about the size of a grain of rice, these solid-state lasers are capable of generating terahertz laser beams with output power exceeding 100 milliwatts. These minute devices should enable the entire hazardous material detector to be held over suspicious packages to instantly determine what's inside. Sandia National Laboratories reports that it and its partners are the only U.S. institutions to have so far demonstrated the ability to fabricate the semiconductor materials necessary to create a terahertz quantum cascade laser. Sandia's expert in molecular beam epitaxy deposition, research scientist John Reno, has perfected the deposition technique for laying down the necessary alternating atomic layers of semiconducting materials onto a gallium arsenide substrate.

"We spent the first year of the Grand Challenge integrating the microelectronics with the device physics to develop the terahertz laser and other components," said Wanke. "Now we are combining them into an integrated terahertz transceiver, the core enabling element for our portable device."

Terahertz radiation lies between microwaves and infrared, and has been harnessed for years by radio astronomers and atmospheric scientists, who have already developed databases of terahertz spectral signatures to identify chemicals in nebulae and planetary atmospheres.

"The current devices are [the size of a] washing machine," said Greg Hebner, program manager for the Grand Challenge. "We are reducing the size, weight and power requirements, as well as expanding the existing spectral databases."

By creating the technology infrastructure, as well as a working prototype, the Sandia program aims to demonstrate a highly integrated miniaturized terahertz transmitter-receiver (transceiver) that could eventually enable handheld devices. Besides detecting concealed weapons or hazardous materials, the handheld terahertz-laser scanning device could also be used in advanced communications and radar systems.

"The infrastructure needed to move the terahertz technology from the laboratory to the field is unavailable right now," said Wanke. "Our project aims to develop that infrastructure and invent the necessary technologies, not only for our hazardous material detector, but also for applications in advanced communication systems and high-resolution radars."

With the miniaturized terahertz quantum cascade laser in hand, Wanke's team is currently integrating its transceiver into a package capable of identifying materials by comparing their spectral signatures to those in their growing database of hazardous substances.

"We are only scratching the surface of what terahertz-based scanners can detect," said Wanke. "This is relatively uncharted territory--there are a lot of scientific discoveries yet to come out of it."

The Terahertz Microelectronics Transceiver Grand Challenge is in its second of three years of funding through Sandia's internal Laboratory Directed Research and Development program, which is supervised by the National Nuclear Security Administration (NNSA).