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Unformatted text preview: Chapter 9 Nonlinear Optics Version 0209.1, 27 Nov 02 Please send comments, suggestions, and errata via email to firstname.lastname@example.org and email@example.com, or on paper to Kip Thorne, 130-33 Caltech, Pasadena CA 91125 9.1 Overview Communication technology is undergoing a revolution, and computer technology may do so soon, in which the key devices used (e.g., switches and communication lines) are changing from radio and microwave frequency devices to optical frequencies. This revolution has been made possible by the invention and development of lasers (most especially semiconductor diode lasers) and the discovery and development of dielectric crystals whose polarization P i is a nonlinear function of the applied electric field, P i = ( ij E j + ijk E j E k + ijkl E j E k E l + ). In this chapter we shall study lasers, nonlinear crystals, and various nonlinear optics applications that are based on them. Most courses in elementary physics idealize the world as linear. From the simple har- monic oscillator to Maxwells equations to the Schr odinger equation, most all the elementary physical laws one studies are linear, and most all the applications one studies make use of this linearity. In the real world, however, nonlinearities abound, creating such phenomena as avalanches, breaking ocean waves, holograms, optical switches, and neural networks; and in recent years nonlinearities and their applications have become major themes in physics research, both basic and applied. This chapter, with its exploration of nonlinear effects in optics, serves as a first introduction to some fundamental nonlinear phenomena and their present and future applications. In later chapters we shall revisit some of these phenomena and shall meet others, in the context of fluids (Chaps. 14 and 15), plasmas (Chap. 22), and spacetime curvature (Chaps. 24, 25, 26). Since highly coherent and monochromatic laser light is one of the key foundations on which modern nonlinear optics has been built, we shall begin in Sec. 9.2 with a review of the basic physics principles that underlie the laser: the pumping of an active medium to produce a molecular population inversion, and the stimulated emission of radiation from the inverted population of molecules. Then we shall describe the details of how a number of different lasers are pumped and the characteristics of the light they emit. Most important 1 2 among these characteristics are high frequency stability and high power. In Sec. 9.3 we shall meet our first example of an application of nonlinear optics: holography. In holography a three-dimensional, monochromatic image of an object is produced by a two step process: recording a hologram, and then passing coherent light through the hologram....
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- Spring '09