Resonant light transmission through a nanohole in a metal film

We show that the maximum wavelength that light can propagate through a rectangular hole in a metal is dramatically increased due to the existence of surface-plasmon waves along the edges of the hole. For a 15 nm wide hole, the cut-off wavelength is more than doubled. Furthermore, we show that there is a Fabry-Perot resonance for light transmission close to the cut-off wavelength, which gives a peak in the transmission. Due to the negative phase of reflection, this resonance exists even for very thin films, smaller than half the wavelength of light. Our analytical theory is verified by numerical simulation and these results agree with recent experiments on the transmission through sub-wavelength rectangular holes.