Light focusing of aluminium film-coated capsule-shaped particles with penetrated cylinder

Abstract Microsphere-assisted imaging technology has proven to be a powerful tool for breaking through the Abbe diffraction limit. Appropriate innovation of microsphere structures is of great significance for the design of microlenses. In this paper, a micro-cylinder was added to the center of the microsphere covered with a patchy aluminium film to form a patchy capsule-shaped particle model. The finite difference time domain simulation method was used to simulate the light field. The research model can effectively improve the relevant parameters of focused beams of various structures (photonic nanojet (PNJ), photonic hook (PH), S-shaped PH. In particular, the effective length can be doubled. By changing the position of the patchy aluminium film, the conversion between PNJ, PH and S-shaped PH can be achieved. By changing the height of the central cylinder, a narrower S-shaped PH and more S-shaped PH inflection points can be produced. This work is expected to have potential applications in the fields of nanolithography, super-resolution imaging, light harvesting, micromachining and other fields.