Nonlinear Near Field Optics

Although usually discussed in the field of microscopy only, near field optics can have a number of other interesting applications in various fields of physics. Among these extensions we discuss here nonlinear near field optics. We show that when working inside the near field lying in the vicinity of a surface, the usual phase matching condition can be overpassed exactly as the Rayleigh criterion is overpassed in scanning near field optical microscopy. This can lead to applications both of technological and of fundamental interest. Principal properties of nonlinear near field optics are presented, and the nonlinear behaviour of a molecule trapped in a tip-sample junction is considered.