Reflection-mode label-free super-resolution microscopy enabled by hollow beam illumination

Recent years have witnessed significant advances in overcoming the resolution limits of traditional optical imaging, particularly in fluorescence-based super-resolution microscopy. In contrast, label-free super-resolution microscopy eliminates the need for sample staining, offering broader applicability. However, most label-free methods often rely on saturation effects or nonlinearity, which limits their applicability. Here, we have developed a reflection label-free super-resolution confocal optical microscopy technique based on super-resolution focusing. Illuminating a conventional objective lens with a hollow beam generates a super-resolution focal spot at its front focal plane. By utilizing the confocal configuration, the same objective lens is used to collect the reflected and scattered light. Experiments demonstrate that the proposed label-free super-resolution confocal microscope resolves a grating with a pitch of 160 nm and a line width of 80 nm. This technology has potential applications in biological and non-biological microscopy.