Dr. Maiman informed him in his best scientific manner that laser action had not been achieved with that one. But the world of promotion won out, and Dr. Maiman allowed the larger device to be photographed on the assumption—or was it hope?—that he would be able to get it to operate in the future. (He did.) The device shown in Figure 16 is the true first laser. The all-important crystal rod is seen at the center. These crystals, incidentally, must be quite free of extraneous material; hence they are artificially “grown”, as shown in Figure 17. The single large crystal is formed as it is pulled slowly from the “melt”, after which it is ground to size and polished. [Illustration: Figure 16 _Dr. Maiman’s first laser. Output was 10,000 watts._] [Illustration: Figure 17 _An exotic crystal of the garnet family is “grown” from a melt at a temperature of 3400°F._] LASING—A NEW WORD 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: _l_ight _a_mplification by _s_timulated _e_mission of _r_adiation. 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. [Illustration: Figure 18 _Sequence of operations in a solid crystal laser. (a) Pumping light raises many atoms to excited state. (b) Lasing begins when a photon is spontaneously emitted along the axis of the crystal. This stimulates other atoms in its path to emit. (c) The resulting wave is reflected back and forth many times between the ends of the crystal and builds in intensity until finally it flashes out of the partially silvered end._] (a) Ruby crystal Pumping light Atom in ground state Excited atom Partial reflecting mirror Full reflecting mirror (b) Excited atom emits photon parallel to axis (c) _Lasing_ begins when an excited atom spontaneously emits a photon parallel to the axis of the crystal (_b_). (Photons emitted in other directions merely pass out of the crystal.) The photon stimulates another atom in its path to contribute a second photon, in step, and in the same direction. This process continues as the photons are reflected back and forth between the ends of the crystal. (We might think of lone soldiers falling into step with a column of marching men.) The beam builds up until, when amplification is great enough (_c_), it flashes out through the partially silvered mirror at the right—a narrow, parallel, concentrated, coherent beam of light, ready for.... SOME INTERESTING APPLICATIONS