IMPORTANCE OF CONFINED FIELDS IN NEAR-FIELD OPTICAL IMAGING OF SUBWAVELENGTH OBJECTS

The detailed imaging process of subwavelength objects deposited on a p lanar surface is studied within the framework of a three-dimensional m odel of scanning near-field optical microscope. The model consists of a truncated pointed fiber approaching a planar surface on which a thre e-dimensional protrusion is deposited. For this geometry, Maxwell's eq uations are solved exactly by applying the field-susceptibility method in the direct space. The technique provides precise evaluations of th e physically relevant near and far fields. In order to refine the unde rstanding of the imaging process of subwavelength objects, we present simulated images of low-symmetry protrusions for two different modes o f polarization and as a function of the approach distance. These simul ations show clearly that subwavelength surface defects induce confined optical near-field distributions that are directly related to the sha pes of the objects. We conclude that the central problem of near-field optical microscopy is the optimal detection of the confined Gelds tha t are set up by the objects themselves.