Near-Field Nano-Focusing and Nano-Imaging of Dielectric Microparticle Lenses.

Compared with traditional far-field objective lenses, microparticle lenses have a distinct advantage of nonobservance of the diffraction limit, which has attracted extensive attention for its application in subwavelength photolithography and super-resolution imaging. In this article, a complete simulation model for a microparticle lens assisted microscopic imaging system was built to analyze the imaging characteristics of any shape of microparticle lens. With this model, we simulated the resolution of a conventional objective lens, a microsphere lens and a hollow microsphere lens, which verified the correctness of our simulation model and demonstrated the super-resolution imaging ability of microsphere lenses. Secondly, the focusing and imaging characteristics of four typical microparticle lenses are illustrated, and how the focal spot affects imaging resolution and imaging quality is analyzed. Upon this conclusion, we reformed and upgraded the microsphere lens with several parameters for smaller focal spots and higher imaging resolution. Finally, three types of microparticle lenses were designed through the optimized parameters and their focusing and imaging characteristics were demonstrated with a minimum FWHM of 140 nm at the focal plane and a highest imaging resolution around 70 nm (~λ/6). Our work opens up a new perspective of super-resolution imaging with near-field microparticle lens.