LASING—A NEW WORD

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Now we can begin to put together the various processes and equipment we have been discussing separately. Perhaps the best way to do this is to look again at the word laser and recall its meaning: light amplification by stimulated emission of radiation. Our objective is to create a powerful, narrow, coherent beam of light. Let us see how to do this. In Figure 18 we imagine a laser crystal containing many atoms in the ground state (white dots) and a few in the excited state (black dots). Pumping light (wavy arrows in a) raises most of the atoms to the excited state, creating the required population inversion.