Abstract The resolution of an optical microscope is constrained by Abbe’s resolution limit, which assumes linear imaging behavior of the optical system. Fluorescence microscopy, the STED (stimulated emission depletion) method, in particular, exploits nonlinear saturation effects during the stimulated emission depletion of fluorescent molecules to achieve a resolution significantly below the Abbe limit. The DFG collaborative project “Nanoscopy of Composite Materials with Thin Photochromic Layers” (NanoVidere) is investigating how the principle of STED nanoscopy can be transferred to reflection microscopy, thus enabling reflection nanoscopy. This approach involves the use of thin photochromic layers, which can be used to dynamically generate a near-field aperture directly on the sample surface. A major challenge has been the number of switching cycles of the photochromic molecules, which has so far permitted only high-resolution line scans rather than area imaging. The consortium has therefore researched and tested a wide range of new photochromic molecules. The results achieved so far already clearly demonstrate the feasibility of reflection microscopy with resolution beyond the diffraction limit. This approach aims to enable nanoscale spectroscopic measurements with nanometer-scale spatial resolution. In this article, we provide an overview of the progress achieved so far.
Rembe et al. (2026) studied this question.