Terahertz lasers could scan for bioweapons

Scientists from the University of Leeds and Harvard University have developed a new teraherz semi-conductor laser that could be able to detect biological agents without causing significant side effects.

The new advance, published in the August issue of the journal Nature Materials, opens the field of teraherz science and technology to a wider range of applications and breakthroughs. Harvard University has already applied for a patent on the device, AZOoptics.com reports.

The new laser will emit THz rays capable of penetrating plastic, clothing and paper and also could be used to help detect tumors, hidden weapons or cracks in various materials. THz radiation can also be used for high-sensitivity detection of concentrations of interstellar material.

Federico Capasso, a member of the research team and one of the first to demonstrate the use of quantum cascade lasers, explained to ScienceBlog.com that the new device emits beams with a much smaller divergence than conventional THz laser sources.

“Unfortunately, present THz semiconductor lasers are not suitable for many of these applications because their beam is widely divergent — similar to how light is emitted from a lamp” Capasso told ScienceBlog.com. “By creating an artificial optical structure on the facet of the laser, we were able to generate highly collimated (i.e., tightly bound) rays from the device. This leads to the efficient collection and high concentration of power without the need for conventional, expensive, and bulky lenses.”

To avoid conventional limitations, the scientists sculpted an array of sub-wavelength groove, dubbed metamaterial, directly on the facet of quantum cascade lasers. They emit in the far-infrared part of the spectrum at a frequency of three THz.

The use of metamaterials was critical in the scientists’ project. While they have potential to be used in applications such as cloaking, illicit substances scanning, quality control for pharmaceuticals and high resolution imaging, their use to date has been limited.

Quantum cascade lasers were first demonstrated by Capasso while he was at Bell labs in 1994. At the shorter wavelengths of the mid-infrared range, these lasers are capable of routinely operating at room temperature with highly optical powers. They are part of a rapidly growing commercial sector for a range of military and civilian applications, including chemical sensing.

The team’s research was partially funded by the United Kingdom’s Engineering and Physical Sciences Research Council and the U.S. Air Force Office of Scientific Research.