Optical nano-imaging via refractive index modulated microsphere compound lens

• The proposed microsphere compound lens (MCL) enhances nano-imaging performance without the need for microspheres to be immersed in liquids, reducing contamination risks. • The novel refractive index modulated design allows for the non-contact working manner, addressing a common limitation of traditional MCLs. • A theoretical model employing wave-optics effects is introduced, providing a solid foundation for the development of the refractive index modulated MCL. • Experimental results demonstrate the resolution and field of view enhancement of the refractive index modulated MCL, marking a substantial advancement in the imaging capabilities of optical microscopes . Microsphere compound lens (MCL) is an effective way to improve microsphere nano-imaging performance. Most of the MCLs require microspheres to be immersed in a liquid and samples are inevitably contaminated. In this paper, a non-contact refractive index modulated design is proposed to enhance the nano-imaging performance of MCL. A theoretical model involving wave-optics effect is adopted to guide the design of refractive index modulated MCL. Experimentally, the refractive index modulated MCL shows a better nano-imaging performance than the same refractive index designed MCL. This new design will benefit improving the imaging performance of the optical microscope.