  In optics, we can generate vortex beams using specific methods such as spiral
phase plates or computer generated holograms. While, in nature, it is worth
noting that water can produce vortices by a circularly symmetrical hole. So, if
a light beam can generate vortex when it is diffracted by an aperture? Here, we
show that the light field in the Fresnel region of the diffracted circularly
polarized beam carries orbital angular momentum, which can transfer to the
trapped particles and make orbital rotation.
