JILA unveils improved frequency comb molecular fingerprinting for trace-gas detection

Boulder, CO--Scientists at JILA and collaborators have demonstrated an improved "molecular fingerprinting" technique based on laser-generated frequency combs that pick out traces of key hydrogen-containing and other molecules from a billion other particles in a gas in just 30 seconds or less (F. Adler et al., Optics Express 18, 21, October 11, 2010). Such performance is suitable for breathalyzers for diagnosing disease, measuring trace gases in the atmosphere, and detecting security threats.

JILA is jointly operated by the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder (CU).

The research extends the range of an existing NIST/JILA invention to cover the mid-IR region of the electromagnetic spectrum, which 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, and can measure lower concentration levels than before.

The heart of the JILA system is an optical frequency comb generated by an ultrafast fiber laser. The setup identifies specific molecules based on which comb "teeth" are absorbed by a gas, and by how much. The light 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 IR (FTIR) spectrometers for many applications, according to the paper.

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 IMRA America (Ann Arbor, MI), 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-IR to the mid-IR. The JILA researchers now plan to extend the system to 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.

SOURCE: NIST Tech Beat; http://nist.typepad.com/tech_beat/2010/10/jila-unveils-improved-molecular-fingerprinting-for-trace-gas-detection.html

Posted by:Gail Overton

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