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 $\pi/N$, where N is an arbitrary positive integer. We show 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.