Implementing caustic illumination in HiLo microscopy

HiLo microscopy is a widefield optical sectioning technique that involves computational reconstruction from two images, one with structured illumination and the other with uniform illumination. A variety of methods, including speckle and periodic grids, can be employed to achieve structured illumination. In this study, we introduce a novel HiLo strategy that utilizes an off-the-shelf holographic diffuser and a low-coherence LED source to generate random caustic patterns. This method offers several benefits over existing ones, such as simplicity and cost-effectiveness. We achieve 4.5 µm optical sectioning capability with a 20x 0.75 NA objective and demonstrate the performance of our method by imaging a 400 µm thick, highly scattering brain section. We anticipate that our caustic-based structured illumination approach will augment the versatility of HiLo microscopy and extend to various imaging applications.