ANALYSIS OF NEAR-FIELD TIP PATTERNS INCLUDING OBJECT INTERACTION USING FINITE-DIFFERENCE TIME-DOMAIN CALCULATIONS

Numerical simulation of the field patterns in the Vicinity of a typica l probe tip of a near field scanning optical microscope is performed u sing the finite-difference time-domain technique. Maps of electric fie ld vectors and Poynting vectors are given for a two-dimensional 120 x 160 cell model of the tip for p-polarized incident illumination with i nitially no object nearby. A metal stripe object is then placed near t he tip and perturbations of the field patterns are displayed, in parti cular those caused by the induction of surface charge density in the m etal object. The metal stripe is scanned across the tip plane at three separation distances and the radiated power, determined by a sum of P oynting vectors across a rear plane, is plotted as a function of later al position of the object. An interesting edge enhancement effect is s een for the close metal object, but not for a dielectric object.