Sensor chirps to sniff out trace gases

Compiled by Photonics Spectra staff

A new “chirping” sensor developed at the National Institute of Standards and Technology detects trace gases hundreds of times more quickly than similar technologies in use today. The sensor is also more sensitive and may make detectors portable, economical and fast enough to be used anywhere.

A trace level of a particular gas can indicate that a problem exists nearby, but many sensors are able to spot only a specific type of gas and, in some cases, only after a long sample analysis time. The new sensor works quickly and efficiently to detect potentially harmful gases.

A still image of the animated graph shows the NIST detector’s linear increase in frequency as a function of time, sweeping from 550 to 561 GHz in frequency over 100 ns. Here it is slowed to 5 s, with an audio chirp used as an analogy to the terahertz chirp. Courtesy of Plusquellic, NIST.

Built from off-the-shelf technology, the sensor can be carried in the user’s hands and can simultaneously detect many different trace gases at very fast rates and with high sensitivity, the researchers said. To do so, it uses terahertz frequencies, which can make gas molecules rotate at rates unique to each type of gas, holding great promise for identifying and quantifying specific gases.

The technology rotates the molecules “in phase” and detects the spinning molecules easily as they gradually fall out of phase with each other. The new technique makes it possible to look at nearly all possible gas molecules instantly using terahertz frequencies. Previously, it was necessary to expose molecules to a range of terahertz frequencies – slowly, one after another. To rapidly expose the molecules to the range of frequencies, the scientists had to teach their off-the-shelf equipment to “chirp.”

They have applied for a patent for their system, which can plug into a power outlet and should be robust enough to survive in a real-world working environment. Findings appeared in the April 22, 2011, issue of Optics Express (doi: 10.1364/ OE.19.008973).