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This paper will review some of the important aspects of infrared lasers. By infrared, I choose to define a wavelength range which is longer than about 2μ, and extends to 1000μ. In this wavelength range, during the past 8 years a large number of laser sources have been discovered, and exploited in applications of investigation of physics and related fields. The most widely used are the gas lasers such as the CO2 laser and the solid state lasers such as the PbSnTe injection lasers. The largest number of laser transi-tions occur in atomic spectra of noble gases. However, from the point of view of power output, the molecular lasers are more important. By molecular lasers, we mean those lasers which operate on transitions between vibrational-rotational levels of molecules. One such example is the carbon dioxide laser at 10.6μ. Since the discovery of the CO2 laser in 1964, the art of molecular lasers has advanced rapidly. It has been shown that the carbon-dioxide laser is capable of producing large amounts CW powers as well as pulsed or Q-switched power, efficiencies of the order of 20%. In addition to the CO2 lasers, other molecular systems have also become important in the last few years, including the HCN laser and the H2O laser which havelaser transitions in the far infrared portion of the region, at wavelengths between 100μ and 1000μ. These laser transitions while not capable of high power output, are nonetheless very important since these are about the only sources of coherent radiation in this part of the spectrum. In the present paper, however, we shall restrict ourselves to a detailed discussion of only the molecular lasers in the 10μ range and in particular to the discussion of carbon-dioxide lasers. We will very briefly dis-cuss the H2O and HCN gas lasers as well as the tunable PbSnTe diode lasers.
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