Principle of least time, 2.2

Principle of least action, 4.2

To figure out the Lagrangian, note that the kinetic energy of a photon is given as (from Phys 101)

where k is the wave number , and the potential energy of a photon is zero.

— Fermat’s principle and the PoLA

— G.-H. Gweon

2011.11.02 Wednesday ACHK