  We demonstrate, both analytically and experimentally, free-space pin-like
optical vortex beams (POVBs).Such angular-momentum-carrying beams feature
tunable peak intensity and undergo robust anti-diffracting propagation,
realized by judiciously modulating both the amplitude and the phase profile of
a standard laser beam. Specifically, they are generated by superimposing a
radially-symmetric power-law phase on a helical phase structure, which allows
the inclusion of an orbital angular momentum term to the POVBs. During
propagation in free-space, these POVBs initially exhibit autofocusing dynamics,
and subsequently, their amplitude patterns morph into a high-order Bessel-like
profile characterized by a hollow-core and an annular main-lobe with a constant
or tunable width during propagation. In contrast with numerous previous
endeavors on Bessel beams, our work represents the first demonstration of
long-distance free-space generation of optical vortex 'pins', with their peak
intensity evolution controlled by the impressed amplitude structure. Both the
Poynting vectors and the optical radiation forces associated with these beams
are also numerically analyzed, revealing novel properties that may be useful
for a wide range of applications.
