Researchers from the University of Michigan have combined two spectroscopic methods to create a technique that could rapidly and accurately detect explosive chemicals and dangerous gases from a distance. Their technique was described in a report in Science published last week.
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Figure 1. The technique developed by Researchers from the University of Michigan could detect dangerous gases from a distance.
Explosives are a global threat
The threat of global terrorism seems to be constantly increasing. The bombs at Brussels airport in 2016 and Manchester arena in 2017 which killed 32 and 22 people respectively, have highlighted the increasing need to detect explosive materials and prevent potentially deadly explosions. Preventing intentional explosions depends on the accurate detection of explosive materials and analysis of post-explosion residues. However, this is not always straightforward as improvised explosive devices often contain non-standard materials that can be difficult to detect.
Furthermore, during detection there is the imminent threat of explosion and the potential presence of toxic chemicals. Techniques for detecting explosives must, therefore, be fast, accurate and able to operate remotely.
The Researchers from the University of Michigan, Professor Steven Cundiff and Dr Bachana Lomsadze, combined multi-dimensional coherent spectroscopy (MDCS) and dual-comb spectroscopy to provide rapid and accurate chemical analysis that can be used from a distance.
Using multi-dimensional coherent spectroscopy to identify gases
MDCS is the optical analog of nuclear magnetic resonance spectroscopy and uses lasers to produce optical signals as a function of two or more pulsed laser frequencies. The optical signals allow gases to be identified from the specific wavelengths of light that the gas absorbs.
If you have light going through the gas, and, for example, you use a prism to separate white light into colored light, in the rainbow spectrum you'd see there'd be black stripes," he said. "Where the black stripes are almost gives you a barcode that tells you what kind of molecule is in the sample.
Professor Steven Cundiff, Researcher, The University of Michigan
Combining MDCS with dual comb spectroscopy for rapid chemical identification
However, identifying gases becomes more difficult when there are mixtures of gases present. "It's like trying to look at three people's fingerprints on top of each other. This is a stumbling block for using these methods in a real-world situation," Cundiff said.
Previously, Scientists have identified gases in mixtures by comparing data collected using MDCS against a catalog of molecules, which can be slow and require high-powered computers. By combining MDCS with dual-comb spectroscopy, Cundiff and Lomsadze were able to reduce the time taken to identify mixtures of gases.
Our method takes about 15 minutes [compared] to a few hours using traditional approaches to MDCS. 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.
Professor Steven Cundiff, Researcher, The University of Michigan
Dual-comb spectroscopy uses two frequency combs to rapidly acquire high-resolution spectra. By combining MDCS and dual-comb spectroscopy, Cundiff and Lomsadze were able to differentiate isotopes of rubidium that cannot usually be distinguished by MDCS as the frequency difference between the two isotopes is too small to be detected.
Cundiff and Lomsadze say that their method can be used to identify chemicals in a mixture without knowing the components of the mixture, which may enable explosive chemicals and dangerous gases to be detected accurately and rapidly.
As the technique relies on laser light passing through the material and does not require contact with the suspect chemical or gas, the method can be used from a distance and could be adapted for use in a handheld device. In future, Cundiff and Lomsadze plan to add another laser to increase the speed of their technique further and enable them to probe infrared light absorptions, increasing the number of chemicals that they can identify.
Image credit: Pixabay.com/WerbeFabrik
References:
Lomsadze B, Cundiff ST, ‘Frequency combs enable rapid and high-resolution multidimensional coherent spectroscopy’ Science 357(6358):1389-1391, 2017.
http://www.azom.com/article.aspx?ArticleID=13543 Accessed October 3rd, 2017.
https://www.eurekalert.org/pub_releases/2017-09/uom-urd092917.php Accessed October 3rd, 2017.
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