Setup of a confocal nanoscope in reflection using a super-oscillatory lens

In this paper, we discuss the setup of a confocal nanoscope in reflection using a super-oscillatory lens (SOL)which offers a sub-diffracted focal spot with an ultra-short depth of focus (≈100 nm). A tolerance of 20 nm defocussing in a 10 μm travel range is thus necessary, translating to an alignment requirement of the stage, with respect to the optical axis, below 2 mrad. We discuss an iterative procedure to fine tune the stage movement to achieve this requirement. We also demonstrate the necessity of the alignment by imaging a 5μm long 1D array of rectangular shaped Au nanostructures with a periodicity of 500 nm.