  We experimentally demonstrate stable trapping and controlled manipulation of
silica microspheres in a structured optical beam consisting of a dark focus
surrounded by light in all directions - the so-called Dark Focus Tweezer.
Results from power spectrum and potential analysis demonstrate the
non-harmonicity of the trapping potential landspace, which is reconstructed
from experimental data in agreement to Lorentz-Mie numerical simulations.
Applications of the dark tweezer in levitated optomechanics and biophysics are
discussed.
