‘‘<i>F</i>=<i>m</i> <i>a</i>’’ optics

Abstract

Fermat’s principle may be used to derive an equation, of the form F=ma, governing the shape of a light ray in a medium of varying refractive index. Many interesting problems in gradient-index optics that ordinarily require considerable computation may therefore be solved very simply by analogy to familiar mechanical problems. This approach also provides the means of thoroughly exploring the optical-mechanical analogy at a much more elementary level than is usual.