Discriminatory optical force for chiral molecules

Robert Cameron, Steve Barnett, Alison Yao

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We suggest that the force F exerted upon a chiral molecule by light assumes the form F = aw + bh under appropriate circumstances, where a and b pertain to the molecule whilst w and h are the local densities of electric energy and helicity in the optical field; the gradients ∇ of these quantities thus governing the molecule’s centre-of-mass motion. Whereas a is identical for the mirror- image forms or enantiomers of the molecule, b has opposite signs; the associated contribution to F therefore pointing in opposite directions. A simple optical field is presented for which ∇w vanishes but ∇h does not, so that F is absolutely discriminatory. We then present two potential applications: a Stern–Gerlach-type deflector capable of spatially separating the enantiomers of a chiral molecule and a diffraction grating to which chiral molecules alone are sensitive; the resulting diffraction patterns thus encoding information about their chiral geometry.

Original languageEnglish
Article number013020
Number of pages18
JournalNew Journal of Physics
Issue numberJanuary
Publication statusPublished - 15 Jan 2014


  • chiral molecules
  • medical physics
  • optical trapping

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