Spatial oscillations in the spontaneous emission rate of an atom inside a metallic wedge

A method of images is applied to study the spontaneous emission of an atom inside a metallic wedge with an opening angle of π/N, where N is an arbitrary positive integer. We show that the method of images gives a rate formula consistent with that from quantum electrodynamics. Using the method of images, we show the correspondence between the oscillations in the spontaneous emission rate and the closed orbits of emitted photon going away and returning to the atom inside the wedge. The closed orbits can be readily constructed using the method of images, and they are also extracted from the spontaneous emission rate.