October 2, 2017

Innovative laser method could rapidly detect dangerous gases

By Glen Dillon (Own work) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons
By Glen Dillon (Own work) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

A laser based method that could be used to quickly and accurately detect chemicals such as explosives and dangerous gases has been developed.

The team from the University of Michigan states that the method could be used in airports, for the environmental monitoring of pollutants, or even on battlefields. The technique’s ability to accurately detect chemicals and gases mean it could also be significant for leak detection in a range of fluid handling applications.

Steven Cundiff and Bachana Lomsadze from the University of Michigan developed the new method, which combines two techniques to speed up the laser-based detection of chemicals. The first, dubbed multi-dimensional coherent spectroscopy (MDCS), uses ultrashort laser pulses to read types of gases “like a barcode.”


"If you have light going through the gas, and, for example, you use a prism to separate white light into coloured light, in the rainbow spectrum you'd see there'd be black stripes," Cundiff said. "Where the black stripes are almost gives you a barcode that tells you what kind of molecule is in the sample."

To speed up the process without losing accuracy, MDCS was combined with a method called dual comb spectroscopy.

Frequency combs are laser sources that generate spectra consisting of equally spaced sharp lines that are used as rulers to measure the spectral features of atoms and molecules with extremely high precision. The use of two frequency combs in dual comb spectroscopy provides a way to rapidly acquire a high resolution spectrum without the need to incorporate mechanical moving elements.

"This approach could allow the method of multidimensional coherent spectroscopy to escape the lab and be used for practical applications such as detecting explosives or monitoring atmospheric constituents," Cundiff said.

Lomsadze and Cundiff applied their method to a vapour of rubidium atoms that contained two rubidium isotopes. The frequency difference between absorption lines for the two isotopes is too small to be observed using traditional approaches to MDCS, but by using combs, Lomsadze and Cundiff were able to resolve these lines and assign the spectra of the isotopes based on how the energy levels were coupled to each other. Their method can be used to identify chemicals in a mixture without previously knowing the makeup of the mixture.

Now, the researchers are planning to add a third laser that could speed up their ability to identify gases even further. Lomsadz and Cundiff also hope to use lasers based on fibre optics to look further into infrared light and in turn expand the number of chemicals they’d be able to identify.

A study detailing Lomsadz and Cundiff’s research has been published in the journal Science.

In the September/October issue of Fluid Handling, experts from KITO look at regulations and best practice for flame arresters in plant piping. Sign-up here to receive a free copy of the magazine.

By Glen Dillon (Own work) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

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