Enhanced reflectivity contrast in confocal solid immersion lens microscopy

The reflected image of a diffraction limited focused spot is investigated using confocal solid immersion microscopy. We find that the spot’s image shows aberrations when reflected off objects with optical indexes lower than that of the solid immersion lens (SIL) material. We demonstrate that such aberrations are only apparent and that the actual size of the spot at the SIL/object interface remains diffraction limited. The aberrations are due to lateral waves at the SIL surface. These von Schmidt waves originate from the total internal reflected components of a diverging spherical wave front. We make use of this image aberration in conjunction with the spatial filtering inherent to confocal microscopy in order to dramatically enhance the optical contrast of objects with low optical indexes.