LAUSR

Abstract Super-hemispherical solid immersion lens (s-SIL) has proved its superiority in high-numerical aperture (NA) and aberration-free characteristics, however, its applications are limited by high cost, difficulty in manufacturing, sample mounting and narrow detection fields. One alternative solution is to utilize a coverslip-based two-piece solid immersion lens (t-SIL) modified from conventional s-SIL. However, one severe issue associated with t-SIL is that its practical imaging performances of t-SIL (e.g. effective NA, aberration, etc.) is not as good as expected. Previous literatures mentioned the problems but gave different explanations. Actually, the fundamental reason is the mismatch among the hemispherical ball, the coupling liquid and the additional coverslip. This work is to investigate the refractive-index-mismatch issues of t-SIL. More specifically, we elaborate two typical cases of mismatches and the corresponding influences on practical aberration and effective NA. In both cases, we prove the feasibility of t-SIL when the refractive indices of three parts are not strictly matched, and give tolerance to mismatch. Besides, solutions to aberration compensation and application suggestions are also given to guide the practical operations.