Microsphere oblique illumination for enhanced optical nano-imaging

Microsphere nano-imaging is a promising technique for label-free and real-time imaging, making optical sub-diffraction resolution possible. Due to the limited size and high surface curvature of microspheres, the magnified imaging suffers from the limited depth of field and low contrast. The performance of this technique depends not only on the geometric parameters of microspheres but also on the illumination conditions of an optical system. In this work, a specially designed filter is added to the microscope to adjust the illumination angle and area on the microsphere. Experimental results demonstrate that with the filter, the imaging contrast is increased by 2.77 times, and the resolution is improved from 125 nm to 100 nm. It also increases the depth of field, extending it from 519 nm to 900 nm coupled with a 20× objective lens. This effective light manipulation strategy establishes suitable illumination conditions to enhance the imaging contrast and resolution. It is also applicable to improve the performance of microspheres in other optical applications.