Light-needles in scattering media using self-reconstructing beams and the STED-principle

Stimulated emission depletion (STED) microscopy generates super-resolved images of single cells by point-wise depletion of fluorescence around a small focal volume. Scanned light sheet microscopy, on the other side, generates images line-wise by scanning a weakly focused laser beam through thousands of scattering cells. Here we address the question, whether fluorescence from an excitation beam can be depleted by a STED beam over tens of micrometers while propagating through scattering material. Therefore, we use two self-reconstructing Bessel beams in cw- mode with different angular momentum for fluorescence excitation and depletion along a distance of 110µm. We show that despite significant scattering at various arrangements of microspheres embedded in agarose gel and despite strong losses in spatial coherence, it is possible to generate a sufficiently good overlap of both beam intensities. Without affecting the self-healing capability of the illumination photons in the Bessel beam’s ring system, the emission of fluorescence photons thereof can be strongly suppressed. This results in a needle-like fluorescence distribution inside scattering media giving new perspectives into fundamental principles and applications in microscopy and metrology.