Observation of laser-induced microscale knotted and unknotted vortex filaments on vaporizing tantalum surface

Laser-induced Ta-surface superheating on a ns time scale is connected with the formation of a spinodal fluid which decomposes into a gaseous phase through microexplosions, generating vortex filament structures on the vaporizing surface. Vortex filaments associated with the Reynolds number Re∼10³–10⁴ are organized into regular, quasiregular, or chaotic structures. Homotopic operations transfer these structures into irreducible ones of a simple closed-loop type, showing that all of them are embedded in a three-dimensional torus either as a vortex ring (unknotted knot), as a cloverleaf (trefoil knotted knot), or as Hopf links (knotted knot). © 1996 The American Physical Society.