Modelling and verification of white light oil immersion microsphere optical nanoscope

摘要

Microsphere has been demonstrated for imaging resolution improvement based on optical microscope, and applied in many engineering and biological fields successfully, while its mechanism is still inconclusive due to the complex physics of both near-field and far-field optics involved. In this paper, a comprehensive simulation model based on point spread function is built to develop a physical insight into microsphere optical nanoscope by numerical simulation. With this model, the Fresnel-region focusing of microsphere lens is studied, which shows the contradiction between focal spot size and focal length. Furthermore, the gap between microsphere and the sample surface is investigated by numerical simulation and experimental verification. As increasing of this gap, the image resolution declines rapidly, and the image becomes blur more and more. At last, a customized sample with a flower pattern etched on silicon substrate is demonstrated with microsphere optical nanoscope, and its feature sizes of 51 nm line width are imaged clearly. While it is generally accepted that microsphere optical nanoscope can be implemented in nano-imaging, these findings quantified the limit on image resolution of this setup, which serves as a general guideline in system design of the other microsphere or micro-particle assisted microscopeanoscope.