Lasers by Hal Hellman, is part of the HackerNoon Books Series. You can jump to any chapter in this book . LASING—A NEW WORD here 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 and recall its meaning: ight mplification by timulated mission of adiation. Our objective is to create a powerful, narrow, coherent beam of light. Let us see how to do this. laser l a s e r In 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 ) raises most of the atoms to the excited state, creating the required population inversion. Figure 18 a 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) begins when an excited atom spontaneously emits a photon parallel to the axis of the crystal ( ). (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. Lasing b 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 ( ), it flashes out through the partially silvered mirror at the right—a narrow, parallel, concentrated, coherent beam of light, ready for.... c About HackerNoon Book Series: We bring you the most important technical, scientific, and insightful public domain books. This book is part of the public domain. Hal Hellman (2021). Laser. Urbana, Illinois: Project Gutenberg. Retrieved October 2022 https://www.gutenberg.org/cache/epub/65512/pg65512-images.html This eBook is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at , located at . www.gutenberg.org https://www.gutenberg.org/policy/license.html

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