Microsphere enhanced optical imaging and patterning: From physics to applications

The diffraction limit is a fundamental barrier in optical science and engineering. It limits the minimum feature size in surface patterning technologies, such as lithography and laser direct writing. It also restricts the resolution for optical imaging, which includes different kinds of microscopes. Microspheres have been demonstrated as a powerful platform to challenge the diffraction limit. Microspheres can manipulate the light in a novel way that conventional optical components cannot achieve. In this review, we summarize the fundamental physical mechanisms and the related applications of microspheres in two primary research directions: first, to focus light energy on the sample surface, which leads to nano-patterning and achieves a sub-100 nm feature size and second, to manipulate light reflected back from the sample surface, which forms the foundation of super-resolution optical imaging to observe nano-structures. We also analyze key features, development, limitation, and opportunities of the nano-patterning and nano-imaging systems based on the microsphere.