  Stimulated emission depletion (STED) microscopy has become a powerful imaging
and localized excitation method beating the diffraction barrier for improved
lateral spatial resolution in cellular imaging, lithography, etc. Due to
specimen-induced aberrations and scattering distortion, it has been a great
challenge for STED to maintain consistent lateral resolution deeply inside the
specimens. Here we report on a deep imaging STED microscopy by using Gaussian
beam for excitation and hollow Bessel beam for depletion (GB-STED). The
proposed scheme shows the improved imaging depth up to ~155{\mu}m in solid
agarose sample, ~115{\mu}m in PDMS and ~100{\mu}m in phantom of gray matter in
brain tissue with consistent super resolution, while the standard STED
microscopy shown a significantly reduced lateral resolution at the same imaging
depth. The results indicate the excellent imaging penetration capability of
GB-STED, making it a promising tool for deep 3D imaging optical nanoscopy and
laser fabrication.
