Scanning Near-Field Optical Probe with Ultrasmall Spot-Size

A novel light emitting probe for scanning near-field optical microscopy is investigated theoretically. The 3D vectorial Helmholtz equation is solved for the new probe geometry using the multiple multipole method. The novel probe consists of a dielectric tip which is entirely metal coated. It provides a single near-field spot which can be smaller than 20 nm (FWHM). The dependence on tip radius, taper angle and metal thickness in front of the tip is investigated for the power transmission through the probe as well as for the spot-size.