Optical binding

A force that may "override" the intrinsic dispersion force (see London Force) is known as optical binding. This involves the irradiation of molecules by a moderately intense laser, in a similar mechanism to laser-assisted resonance energy transfer (see All-optical Switching).

Feynman diagram for optical binding

The optical binding mechanism is shown on the left:

  • Region I (before interaction i) - the right and left molecules are unexcited (blue)
  • Region II (between i and j) - a laser photon is absorbed by the right molecule and it moves into an intermediate state (green)
  • Region III (between j and k) - a photon is emitted by the right molecule and it returns into the unexcited state (blue)
  • Region IV (between k and l) - this photon is absorbed by the left molecule and it moves into an intermediate state (green)
  • Region V (after l) - a laser photon is stimulated from the left molecule and returns into the unexcited state (blue)

The energy shift (similar to the matrix element) for optical binding involves two alpha tensors - due to two interactions at each molecule - and one V tensor (since the molecules interact via one photon).

The energy shift is already a measurable quantity and, therefore, does not need to be squared to find the transfer rate.


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