Tying the Knot -- with Computer-Generated Holograms

Ÿ Optical traps created from strongly focused beams of light now can be sculpted into arbitrary three-dimensional patterns, including knots.  Intensity gradients in the pair of interlocking ring traps shown in (a) exert forces that gather and hold microscopic objects, such as the colloidal spheres shown in (b).  Phase gradients encoded in the hologram drive the particles around the ring, threading the knot as shown schematically in (c).

ŸFirst practical implementation of a knotted force field.

ŸApplications for knotted force fields include force measurements for medical diagnostics, mixers for lab-on-a-chip applications, and induction of knotted current loops for fusion power generation.

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