  Optical energy flow inside a dielectric microsphere is usually codirected
with the optical wavevector. At the same time, if the optical field in a
microsphere is in resonance with one of the high-quality spatial eigenmodes
(whispering-gallery modes - WGMs), a region of reverse energy flow emerges in
the shadow hemisphere. This area is of considerable practical interest due to
increased optical trapping potential. In this Letter, we consider a perforated
microsphere with an air-filled single pinhole fabricated along the particle
diameter and numerically analyze the peculiarities of WGM excitation in a
nanostructured microsphere. A pinhole isolates the energy backflow region of a
resonant mode and changes a perforated microsphere into an efficient optical
tweezer. For the first time to our knowledge, we reveal the multiple
enhancement of backflow intensity in the pinhole at a WGM resonance and discuss
the way for its manipulation.
