  Light fields with extraordinary propagation behaviours such as nondiffracting
and self-bending are useful in optical delivery for energy, information, and
even objects. A kind of helical beams is constructed here based on the caustic
method. With appropriate design, the main lobe of these helical beams can be
both well-confined and almost nondiffracting while moving along a helix with
its radius, period, the number of rotations and main lobes highly adjustable.
In addition, the main lobe contains almost half of the optical power and the
peak intensity fluctuates below 15% during propagation. These promising
characteristics may enable a variety of potential applications based on these
beams.
