  Optical energy flow inside a dielectric microsphere exposed to an optical
wave is usually codirected with its wave vector. At the same time, if the
optical field in a microparticle is in resonance with a high-quality spatial
eigenmode, referred to as the whispering-gallery mode (WGM), at least two
regions of reverse energy flow emerge in the illuminated and shadow particle
hemispheres. These areas are of considerable practical interest due to their
enhanced optical trapping potential provided they should be previously cleared
from particle material. In this paper, we consider a perforated microsphere
with an air-filled pinhole fabricated along the particle diameter and
theoretically analyze the conditions for WGMs excitation. A pinhole isolates
the energy backflow regions of WGM and multiple enhances the optical pull-in
force that transforms a perforated microsphere into an efficient optical
tweezer for trapping various nanoobjects.
