  The diffraction limit is a fundamental barrier in optical microscopy, which
restricts the smallest resolvable feature size of a microscopic system.
Microsphere-based microscopy has proven to be a promosing tool for challenging
the diffraction limit. Nevertheless, the microspheres have a low imaging
contrast in the air, which hinders the application of this technique. In this
Letter, we demonstrate that this challenge can be effectively overcome by using
partially Ag-plated microspheres. The deposited Ag film acts as an aperture
stop that blocks a portion of the incident beam, forming a photonic hook with
oblique near-field illumination. Such a photonic hook significantly enhanced
imaging contrast, as experimentally verified by imaging Blu-ray disc surface
and silica particle arrays.
