Mid-infrared Spectroscopy

As mentioned in a previous post on vibrational spectroscopy, one can use the infrared spectrum to determine the molecular structures, which may offer clues about the 'fingerprints' of the molecules. Compared to the weak vibrational overtone transitions which give rise to near infrared radiation, the mid-infrared gives much stronger signals that serves enough S/N ratio and works as the 'fingerprint' region of molecules. As an example, you can have a look at the absorption spectrum of Methane.

Absorption Spectrum of Methane

The biggest problem for laser spectroscopy in the mid-infrared is the lack of good laser sources in this spectrum range.

F.K. Tittel et al. has listed the available mid-infrared laser sources in the mid infrared in a book chapter, which is also given below:

Laser sources and their working range, courtesy[F.K. Tittel et al.]

Based on an excellent laser they developed in 2009, F. Adler et al. from JILA, Colorado has successfully developed a state-of-art mid-infrared laser spectroscopy. The work is excellent and the paper written is a classic to me, that's really worth to share with you in a summary of the paper in one short document: Google Drive--Mid-infrared Frequency comb Fourier Transform spectroscopy.