Surface-enhanced optical microscopy

A new concept is proposed for an optical probe with spatial resolution unlimited by diffraction effects. It is based on optical-field confinement by surface plasmons of a submicrometer-sized metal particle. The particle serves as an antenna that receives an incoming electromagnetic field. The field extends to a nearby sample surface and interacts with a small area on that surface through the nonlinear susceptibility tensors. The induced sample polarization is reradiated by the particle, thereby generating a Raman, a two-photon, or a second-harmonic spectrum. Microscopy is performed by rastering the position of the metal particle over the sample surface. Spatial resolution approaching 1 nm is projected. The concept is also applicable to submicrometer optical lithography and ultrahigh-density optical recording.