Interaction of two edge dislocations in free-space propagation

This paper studies in detail the interaction of two edge dislocations nested in a Gaussian beam propagating in free space.It shows that in free-space propagation the edge dislocations are unstable and vanish,and two noncanonical vortices with opposite topological charge take place when off-axis distances c 1 and c 2 of two edge dislocations are nonzero,and the condition k 2 w 8 0 + 32c 1 c 2 (w 2 0 2c 1 c 2)z 2 > 0 is fulfilled (k-wave number,w 0-waist width).A noncanonical vortex appears when one off-axis distance is zero.However,one edge dislocation is stable when two edge dislocations are perpendicular and one off-axis distance is zero.Two perpendicular edge dislocations both with zero off-axis distance are also stable.The analytical results are illustrated by numerical examples.