Researchers at Sandia National Laboratories in Albuquerque, US, are developing the next generation of security screening devices that could be used to identify hazardous and toxic materials, even when the materials are hidden by clothing and packaging materials.
Working in the terahertz (THz) portion of the electromagnetic spectrum, the Sandia Labs team, led by Mike Wanke, are working on a portable transceiver that could be used in a variety of environments.
Currently 18 months into a three-year project, Wanke’s goal is to demonstrate a laboratory prototype by the end of the third year. Patents have been applied for, and the Sandia researchers have already begun working with industrial partners to exploit the technology.
The transmitter consists of a miniature quantum cascade laser (QCL) with an output power in excess of 100 milliwatts, and Wanke and his colleagues are now working on the receiver. ‘We are essentially making a heterodyne transceiver,’ says Wanke. ‘In our case we are using a Schottky diode -– which can operate at room temperature – as the detecting mixer.’
According to Dutch terahertz expert Merlijn Hajenius, based at the Technical University of Delft, Schottky diodes are in some ways better than the cryogenically-cooled bolometers typically used in terahertz detectors, but the sensitivity of Schottky diodes decreases exponentially at higher frequencies.
Spectral resolution depends on the stability of the system’s local oscillator, and for gas phase spectroscopy at low pressures, megahertz accuracy is more than adequate, says Wanke: ‘We have measured the intrinsic line-width of a THz QCL to be less than 10 kHz, and other work with QCLs has shown that MHz stability is achievable without requiring active feedback.’
Tom Crowe, President of Virginia Diodes, comments: ‘The work at Sandia is fundamental to opening the frequency band for scientific, defence, security and commercial applications. Once terahertz technology is fully established, this part of the spectrum will be as useful as the microwave and infrared frequency bands are today.’
Photo: Mike Wanke, Principal-Investigator of the Terahertz Microelectronics Transceiver Grand Challenge, holds a miniaturised device that will eventually replace large pieces of equipment like those in the background (including the coffee machine!). © 2007 Bill Doty/Sandia National Laboratories.
Article first published in Nanomaterials News.