Geometrical optics

Article By:

Shack, Roland V. Optics Science Center, The University of Arizona, Tucson, Arizona.

Last reviewed:June 2020

DOI:https://doi.org/10.1036/1097-8542.286900

The geometry of light rays and their images, through optical systems. Geometrical optics is by far the oldest model proposed for accounting for the behavior of light, going back to classical Greece. It was not until around the beginning of the nineteenth century that the wave nature of light was seriously considered, and in the modern view of the nature of light, geometrical optics as a fundamentally correct model is simply wrong. In spite of this geometrical optics is remarkably robust, remaining as a most practical tool in the solution of optical problems. It has been applied to analyzing laser resonators, to solving problems in interference and diffraction, and even to analyzing the behavior of waveguides, where at first glance it would seem to be totally inappropriate. These developments have been made possible by the generation of “fictitious” rays (all rays are fictitious) or by attributing to rays properties which cannot be accounted for in a strictly geometrical optical model. Nevertheless, the principal application of geometrical optics remains in the field of optical design, where it has been employed since the first optical instruments were developed in the early seventeenth century. This article concentrates on this application. See also: Diffraction; Interference of waves; Laser; Waveguide

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