Model for reflection near field optical microscopy.

We discuss a model that describes the optical interactions between a dielectric tip and a surface exhibiting roughness of subwavelength size (infinite tracks). Such a model gives new insight into the resolution achievable by scanning near field optical microscopy. The dielectric tip is schematized as a cone whose extremity reduces to a small sphere acting as a dipolar scattering center, allowing separation of the contributions from the near field lying at the air-sample interface of other long range terms associated with the progressive waves coming from the surface. It is shown that because of its fast spatial dependence, the near field detected by the tip contains subwavelength features of the object. Relationships with preliminary experiments are discussed.