The mid-infrared region of the electromagnetic spectrum is a critical range because it includes the frequencies associated with strong molecular vibrations, including various hydrogen bonds.

Florian Adler and co-workers, National Institute of Standards and Technology and University of Colorado, USA, have used ultrafast lasers to form a frequency comb Fourier transform spectrometer which operates in the 2100-to-3700-cm^-1 region with a maximum resolution of 0.0056 cm^-1. The comb is based on a non-linear optical process that shifts the light from the near-infrared to the mid infrared.

Near-real-time acquisition of broadband absorption spectra was achieved with part-per-billion detection limits in 30 s of integration time for methane, ethane, isoprene, and nitrous oxide. This level of performance would allow the device to be used in human breath analysis, e.g., detecting asthma (ethane) or kidney failure (methanol).

• Mid-infrared Fourier transform spectroscopy with a broadband frequency comb
  F. Adler, P. Masłowski, A. Foltynowicz, K. C. Cossel, T. C. Briles, I. Hartl, J. Ye,
  Opt. Express 2010, 18, 21861-21872.
  DOI: 10.1364/OE.18.021861