Surface-plasmon enhanced harmonic generation at a rough metal surface

In this paper, we compute the second harmonic radiation generated at a roughened metal surface which is describable in terms of randomly distributed height and spacing roughness variables. The roughness of the surface allows incident radiation to be coupled to a surface-plasmon mode in the metal at frequency ω that beats with the fundamental field at the same frequency to produce a 2ω field of frequency which radiates from the metal in a narrowly defined direction. Given appropriate rough surface parameters, the latter radiation can in principle serve as a well-collimated coherent source of radiation at the second harmonic frequency. We compare the collimated intensity of the harmonic produced by the roughness-induced plasmon coupling with that produced by specular reflection from the metal surface. The former intensity is predicted to exceed the latter by as much as 2 orders of magnitude.