Laser-based Mid-infrared Sources and Applications

7Mid‐IR Applications

The development of laser‐based sources in the mid‐infrared opened up unprecedented possibilities in many fields including spectroscopy and trace‐gas detection, atmospheric science, greenhouse gas and pollution monitoring, homeland security, hyperspectral imaging, infrared countermeasures, free‐space optical communications, biomedical diagnostics, surgery and neurosurgery, industrial process control, the study of combustion dynamics, organic material processing, and investigation of metamaterials, among others. This chapter reviews the most important applications of the mid‐IR.

7.1 Spectroscopic Sensing and Imaging

Vibrational spectra provide fingerprints of molecular structures, and as such they are used extensively in science and technology. Coherent laser sources in the mid‐IR, especially in the 3–20 μm spectral range, have long been recognized as important tools for both fundamental and applied spectroscopy and sensing. The vast majority of gaseous chemical substances exhibit fundamental vibrational absorption bands in that region, and the absorption of light by these bands provides a nearly universal means for their detection. The main advantage of optical techniques is the nonintrusive in situ detection capability for trace gases and their isotopologues (molecules that contain isotopes). As an illustration, the fundamental absorption spectra, associated with transitions between rotational–vibrational states, for 11 small molecules are shown in