  Nonlinear structured illumination microscopy (nSIM) is an effective approach
for super-resolution wide-field fluorescence microscopy with a theoretically
unlimited resolution. In nSIM, carefully designed, highly-contrasted
illumination patterns are combined with the saturation of an optical transition
to enable sub-diffraction imaging. While the technique proved useful for
two-dimensional imaging, extending it to three-dimensions (3D) is challenging
due to the fading/fatigue of organic fluorophores under intense cycling
conditions. Here, we present a compressed sensing approach that allows for the
first time 3D sub-diffraction nSIM of cultured cells by saturating fluorescence
excitation. Exploiting the natural orthogonality of transverse speckle
illumination planes, 3D probing of the sample is achieved by a single
two-dimensional scan. Fluorescence contrast under saturated excitation is
ensured by the inherent high density of intensity minima associated with
optical vortices in polarized speckle patterns. Compressed speckle microscopy
is thus a simple approach that enables 3D super-resolved nSIM imaging with
potentially considerably reduced acquisition time and photobleaching.les fast
3D super-resolved imaging with considerably minimized photo-bleaching.
