Improved performance in microsphere-assisted 2D and 3D imaging by polystyrene microspheres semi-immersed in SU-8 resist

Abstract

In this work, we introduce a method to improve the performance of microsphere-assisted imaging by optimizing the refractive index of immersion media. In the method, polystyrene (PS) microspheres are semi-immersed in water, spin-on-glass, SU-8 resist, and S1805 resist. We experimentally find that the distortion of the image observed by a PS microsphere semi-immersed in SU-8 resist is the smallest while the resolution of the semi-immersed microsphere is the highest. ZEMAX software simulations show that PS microspheres semi-immersed in SU-8 resist have the smallest distortion and spherical aberration. Moreover, numerical simulations also reveal that they have the strongest peak intensity, the narrowest waist, and the shortest focal length of the photonic nanojet. When the semi-immersed PS microsphere is used in microsphere-assisted microscopy, a 200-nm-diameter hexagonally close-packed (hcp) silica nanoparticle array can be clearly distinguished. When they are used in microsphere-assisted interference microscopy, a 250-nm-diameter hcp silica nanoparticle array can be resolved.