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

Microsphere lenses can overcome the optical diffraction limit and observe features smaller than 200 nm under white light. Inclined illumination benefits from the second refraction of evanescent waves in the microsphere cavity, which avoids the influence of background noise and can improve the imaging resolution and imaging quality of the microsphere superlens. Currently, microsphere imaging under inclined illumination is always performed using barium titanate microspheres immersed in an aqueous environment. However, the background medium of the microlens varies according to diverse applications. This study investigates the effects of background media on the imaging properties of microsphere superlens under inclined illumination. Experimental results demonstrate that the axial position of the microsphere photonic nanojet changes with the background medium, leading to a change in the magnification and objective distance. The imaging performance of microspheres is related to the refractive index of the immersion medium instead of the material. This study helps to endow microsphere superlens with a more universal application ability.