Detection of vortex beams based on mutual interference

Abstract

The mutual interference method is introduced to detect vortex beams. For the coaxial interference between l1-order and l2-order vortex beams, the intensity distribution is spirally fan-shaped. The partition number N=|l2-l1|, and the spiral direction can distinguish the sign of topological charge with larger absolute value between |l1| and |l2|. Fork-shaped fringes appear in the center for the small-angle interference between vortex beams with incident angle β1 and β2. The forking number between two fringes agrees with N=|l2-l1|, and the forks face upward when l1<l2 & β1>β2, or l1>l2 & β1<β2, and face downward when l1>l2 & β1>β2, or l1<l2 & β1<β2. Especially, when one of the beams is a Gaussian beam, such as l1=0, the value and sign of the topological charge l2 of the other vortex beam can be simply detected. The mutual interference method can conveniently detect the value and sign of vortex beams without borrowing redundant devices.