Alkali-metal atoms optical pumping

Measurement of atomic densities by optical absorption A knowledge of the densities of atoms in the ground and metastable levels is often essential for the interpretation of data in atomic collision experiments. This is particularly true for the alkali metals where optical pumping experiments are frequently used to determine collision cross-sections. Since data obtained from vapour pressure tables are unreliable, the required densities are often obtained by measuring the absorption of the gas or vapour when illuminated by light of the resonance or other suitable lines. 

Chemical lasers are pumped by reactive processes, whereas in photodissociation lasers the selective excitation of certain states and the population inversion are directly related to the decomposition of an electronically excited molecule. Photolysis has been the only source of energy input employed in dissociation lasers, although it appears quite feasible to use other energy sources, e.g. electrons, to generate excited states. Table 4 lists the chemical systems where photolysis produces laser action. It is appropriate to begin the discussion of Table 4 with the alkali-metal lasers since Schawlow and Townes in 1958 35> chose the 5 f> 3 d transitions of potassium for a first numerical illustration of the feasibility of optical amplification. These historical predictions were confirmed in 1971 by the experimental demonstration of laser action in atomic potassium, rubidium and cesium (Fig. 14). 

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