Hamiltonian optics

Summary

Hamiltonian optics describes light rays as the trajectories of a Hamiltonian system. A ray is given by a position and an optical momentum, the direction of the ray times the refractive index. With a coordinate along the optical axis playing the role of time, the rays obey Hamilton's equations. This brings the tools of classical mechanics into optics: phase space, invariants such as the etendue, and characteristic functions of an optical system. See the definition.