Imaging Properties of Microsphere Superlens with Varying Background Refractive Indices under Inclined Illumination

Microsphere lenses can overcome the optical diffraction limit and can be used to observe features smaller than 200 nm under white light. Inclined illumination benefits from the second refraction of evanescent waves in the microsphere cavity, prohibiting the influence of background noise and improving the imaging resolution and quality of the microsphere superlens. Currently, there is a consensus that microspheres immersed in a liquid environment can improve imaging quality. Microsphere imaging under inclined illumination is performed using barium titanate microspheres immersed in an aqueous environment. However, the background medium of a microlens varies depending on its diverse applications. In this study, the effects of continuously changing background media on the imaging properties of microsphere lens under inclined illumination are investigated. The experimental results demonstrate that the axial position of the microsphere photonic nanojet changes with respect to the background medium. Consequently, owing to the refractive index of the background medium, the imaging magnification and the position of the virtual image change. Using a sucrose solution and polydimethylsiloxane with the same refractive index, we demonstrate that the imaging performance of microspheres is related to the refractive index rather than the background medium type. This study helps associate microsphere superlenses with a more universal application spectrum.