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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.