JILA Unveils Improved Molecular Fingerprinting for Trace Gas Detection

Optical frequency comb aids in atmospheric, security applications

Published: Thursday, October 21, 2010 - 15:46

(NIST: Gaithersburg, MD) -- Scientists at JILA and collaborators have demonstrated an improved laser-based “molecular fingerprinting” technique that picks out traces of key hydrogen-containing molecules and other molecules from a billion other particles in a gas in just 30 seconds or less—performance suitable for breathalyzers for diagnosing disease, measuring trace gases in the atmosphere, detecting security threats, and other applications. JILA is a joint institute of the University of Colorado at Boulder and the National Institute of Standards and Technology (NIST).

Described in Optics Express, the research extends the range of an existing NIST/JILA invention to cover the mid-infrared region of the electromagnetic spectrum. This is a critical range, because it includes the frequencies associated with strong molecular vibrations, including various hydrogen bonds. The technology thus can identify a much wider variety of molecules, including virtually any containing hydrogen—the most common element in the universe—and can measure lower concentration levels than before.

The heart of the JILA system is an optical frequency comb, a tool generated by ultrafast lasers, which precisely identifies a wide range of different colors of light. Researchers identify specific molecules based on which colors of light, or comb "teeth," are absorbed by a gas, and in what amounts. The comb light usually passes through a gas mixture many times, significantly improving detection sensitivity. Concentrations are measured with the help of molecular "signatures" assembled from databases. The technique works quickly and reliably even when molecules have overlapping, continuous, or otherwise confusing absorption signatures. The rapid data collection, in particular, makes the technology suitable to replace or surpass conventional Fourier transform infrared (FTIR) spectrometers for many applications, according to the paper.

Artist’s rendering of JILA’s molecular fingerprinting system. A gas mixture (left) is probed by a frequency comb, a laser-based tool for identifying different colors of light. By analyzing the amounts of specific colors absorbed, the system quickly identifies molecules and their concentrations. Applications may include diagnosing disease, detecting security threats, and measuring trace gases in the atmosphere. Credit: Baxley/JILA

In the demonstration, scientists measured a dozen important molecules at parts‐per‐billion precision, including the greenhouse gases methane, carbon dioxide, and nitrous oxide; and the pollutants isoprene and formaldehyde. In addition, the system detected molecules useful in human breath analysis: ethane (a sign of asthma) and methanol (a sign of kidney failure). The system is able to reach parts-per-trillion sensitivity for the first time in detecting carbon dioxide.

Collaborators from Ann Arbor, Michigan-based IMRA America Inc. developed the fiber laser used to make the frequency comb. The comb itself is based on a nonlinear optical process that shifts the light from the near infrared to the mid infrared. The JILA researchers now plan to extend the system further into longer wavelengths to cover a second important molecular fingerprinting region, to identify a more diverse set of complex molecules containing carbon, and to modify the equipment to make it portable. Planning is also under way for clinical trials of the breathalyzer application.

The research is funded by the U.S. Air Force Office for Scientific Research, Defense Advanced Research Projects Agency, the Agilent Foundation, NIST, and the National Science Foundation.

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NIST

Founded in 1901, the National Institute of Standards and Technology (NIST) is a nonregulatory federal agency within the U.S. Department of Commerce. Headquartered in Gaithersburg, Maryland, NIST’s mission is to promote U.S. innovation and industrial competitiveness by advancing measurement science, standards, and technology in ways that enhance economic security and improve our quality of life.