ABSTRACT
Infrared light is broadly dened as radiation with a frequency ranging from the nominal edge of the visible spectrum to the microwave, covering 750 nm to 1 mm. Near infrared (NIR) covers the wavelength range from 0.75 to 1.4 µm; short-wavelength infrared (SWIR) covers 1.4 to 3 µm; midwavelength infrared (MWIR) covers from 3 to 8 µm; long-wavelength infrared (LWIR) covers from 8 to 15 µm; and far infrared (FIR) usually covers from 15 to 1000 µm. Mid-IR covers two important atmospheric transmission windows (see Figure 14.1) and the spectral region of the vibrational absorption bands of many gases, liquids, and solids (some strong bands of O2, CO2, and H2O are shown in Figure 14.1). Mid-IR spectroscopy, therefore, provides sensitive chemical analysis for a wide range of applications, e.g., for green house gases, soil contaminants, water pollution, air pollution, pharmaceuticals, toxic agents, and biological molecules for diagnosis. The potential applications are numerous, such as monitoring manufacturing processes, air quality, exhaust from plants and engines, explosives, narcotics, etc. High-power lasers operating at the strong water absorption at ~3 µm are ideal for precision surgical operations. Lasers with high power and wide tunablity within the atmospheric transmission windows are critical for countermeasures against heat seeking missiles.
