Knotted and linked phase singularities in monochromatic waves

Abstract

Exact solutions of the Helmholtz equation are constructed, possessing wavefront dislocation lines (phase singularities) in the form of knots or links where the wave function vanishes (‘knotted nothings’). The construction proceeds by making a non-generic structure with a strength n dislocation loop threaded by a strength m dislo-cation line, and then perturbing this. In the resulting unfolded (stable) structure, the dislocation loop becomes an (m,n) torus knot if m and n are coprime, and N linked rings or knots if m and n have a common factor N; the loop or rings are threaded by an m-stranded helix. In our explicit implementation, the wave is a superposition of Bessel beams, accessible to experiment. Paraxially, the construction fails.