Imaging of two-dimensional nanoplasmonic structures by nanoscopy with contact microlenses and various microscope objectives

The use of contact microlenses attracted a great deal of attention recently because in the case of imaging nanoplasmonic structures it showed the resolution values exceeding the classical diffraction limit. The mechanisms that allow for this type of imaging are presently still debated in the literature; these range from photonic nanojets, plasmon-polaritons, localized surface plasmon resonances and coherent modal excitation in metallic objects, as well as optical resonances in microsphereical lenses. The system of interest is metallic nanoobjects coupled to a dielectric microsphere and is considered as a directional antenna. In this work, we performed preliminary studies of how the resolution of this method depends on the numerical aperture of the microscope objective. We used 2D periodic nanoplasmonic arrays. Based on assumption of incoherent imaging, we demonstrated that the resolution is reduced from ~λ/7 to ~λ/4 for a reduction of NA from 0.95 to 0.60. In future work, we plan to test the main conclusions of this work using standalone and long-period structures.