Microsphere assisted optical super-resolution imaging with narrowband illumination

Microsphere assisted microscopy is a facile and affordable super-resolution technique. Here, we explored fully liquid-immersed high-index (n=1.9, 2.1) microsphere assisted super-resolution imaging with narrowband light illumination. The influence of illumination wavelengths and the relative refractive index between microspheres and immersion media on imaging are experimentally investigated, as well as the relationship between the magnification generated by microspheres and imaging position. Blu-ray disk with 120 nm/180 nm stripe structure can be resolved with low-numerical-aperture (NA) microscope objective (10x, NA=0.35) with appropriate imaging parameters, which achieves super-resolution observation in a low-cost and convenient way. The combination with high relative refractive index between microsphere (n=2.1) and immersion medium (n=1.33) shows the best resolution and magnification (similar to 8). In addition, the dark spot generally appearing in the center of the microsphere in super-resolution imaging is studied. Thus we propose the approach to obtain optimal super-resolution imaging effect by combining narrowband short-wavelength illumination and high relative refractive index between microspheres and immersion media.