Middle infrared tunable laser spectroscopy for molecular sensing: from space to terrestrial applications.

Fundamental rotational-vibrational absorption bands of molecules have long been recognized as ideal to carry out quantitative, sensitive, and selective probing of molecular properties. As such, the spectral range covered by these bands is often referred as the “fingerprint” region. Within this region, atmospheric windows (3-5 µm and 8-12 µm) where water vapour spectral interferences remain minimal are of particular interest for the development of practical spectroscopy-based sensors. The advent, and subsequent maturation, of novel continuously tunable semiconductor laser sources operating in the fingerprint region has unlocked a wide breadth of applications spanning from fundamental ro-vibrational spectroscopy studies to deployment of operational molecular sensors.
The laser spectroscopy team at the space science and technology department of the Rutherford Appleton laboratory undertakes a wide portfolio of research and development projects towards novel molecular sensing methods and instruments, primarily using quantum cascade lasers. Whilst science drivers and applications underpinning this activity have primarily belonged to the space and atmospheric science areas, increasingly, many applications for which compact, deployable, real time sensing is needed are spun off. A review of the team activity covering coherent passive and active remote sounding, open-path, and in-situ molecular sensing will be presented, as well as insights on technological developments towards miniaturization and processing algorithms needed for operational field deployment of middle infrared tunable laser spectrometers.