LAUSR

Fluorescence nanoscopy methods based on the RESOLFT principle, such as beam‐scanning STED nanoscopy, require the co‐alignment of optical beams for molecular state (on/off) switching and fluorescence excitation. The complexity and stability of the beam alignment can be drastically simplified and improved by using a single‐mode fibre as the sole light source for all required laser beams. This in turn then requires a chromatic optical element for shaping the off‐switching beam into a focal‐plane donut while simultaneously leaving the focal intensity distributions at other wavelengths shaped as regular focal spots. Here we describe novel designs of such so‐called ‘easySTED phase plates’ and provide a rationale how to find the desired spectral signature for combinations of multiple wavelengths.