Radiation coupling and image formation in scanning near-field optical microscopy

The propagation of light through an aperture scanning near-field optical microscope is studied. Rules for optimizing the confinement and throughput of aperture near-field probes are derived. The radiation from the aperture through simple sample structures, a flat substrate and a substrate with stripe-like elevations and depression, into classically allowed and forbidden directions is determined quantitatively. It is shown that small amplitude and phase objects can be distinguished by comparing "allowed" and "forbidden" light images.