Laser materials in general

In choosing fhe examples of lasers discussed in Sections 9.2.1 to 9.2.10 many have been left ouf. These include fhe CO, H2O, HCN, colour cenfre, and chemical lasers, all operating in fhe infrared region, and fhe green copper vapour laser. The examples fhaf we have looked af in some defail serve to show how disparate and arbifrary fhe materials seem to be. For example, fhe facf fhaf Ne atoms lase in a helium-neon laser does nof mean fhaf Ar, Kr and Xe will lase also - fhey do nof. Nor is if fhe case fhaf because CO2 lases, fhe chemically similar CS2 will lase also. 

The potential for laser acfivify is nof anyfhing we can demand of any atom or molecule. We should regard if as accidenfal fhaf among fhe exfremely complex sefs of energy levels associated wifh a few atoms or molecules fhere happens to be one (or more) pairs befween which if is possible to produce a population inversion and fhereby create a laser. 

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