Throughout much of our discussion of optics in Chapters 22-24 we assumed monochromatic light emitted coherently (in phase). In reality, this is a very rare kind of light. Most light, whether from the sun, from fluorescent lamps, or from incandescent bulbs, comes from large numbers of atoms randomly radiating photons. However, with the invention of the laser in 1960, a practical source of coherent light became available, and physicists took a renewed interest in optics. The coherence of laser light made possible many new experiments. For example, laser light can be focused into beams of extremely high intensity, a feature that has led to basic discoveries concerning the nature of the interaction between light and matter. It has also led to practical applications such as drills for making microscopic holes in the hardest substances and surgical instruments for delicate and precise operations.

One of the better-known applications of lasers is the production of three-dimensional images, called holograms. Holography is a rapidly growing field, with scientific and commercial applications. In this chapter, we present the basic ideas of holography, in which the modern tool of laser light is combined with the classical principles of diffraction.

The development of the laser would not have been possible without an understanding of quantum mechanics and atomic physics. Similarly, our understanding of other optical phenomena, such as color and vision, has also advanced through our knowledge of quantum physics. The importance of color and how we see it has grown along with the explosive growth of information in the late twentieth century. The use of color enhances our ability to assimilate information rapidly, as false-color images have demonstrated. Color has become an important tool for presenting information in all areas of life.