Phase distribution of vortex beams (radians). Left to right) imposed
phase distribution on the array’s discrete elements, measured phase
distribution at the focal plane before and after applying phase corrections, and
simulation for (top to bottom) M = 0, 1, and 4. Before applying phase
corrections, there are slight variations in the phase distribution along the
radial direction. The smooth phase transition indicates that the array behaves
as a continuous acoustic source.