Discriminatory optical force for chiral molecules

Abstract

We suggest that the force F exerted upon a chiral molecule by light assumes the form F = a∇w + b∇h 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 mirrorimage 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.

Enhanced Optical Chirality through Locally Excited Surface Plasmon Polaritons

“…This gains special significance as it implies that chirality flow can lead to opposite forces on molecules of different handedness 39 . Such handedness-dependent forces have been investigated and interpreted through different approaches 8,11,13,39,40 . The chirality flow of the CSPP is shown in Figure 2e.…”

Optofluidic sorting of material chirality by chiral light

“…Indeed, despite an obvious practical interest there are only a few theoretical works dealing with electromagnetic field-induced mechanical separation of nanometre-sized chiral entities 14,15,[18][19][20][21][22][23] , whereas no experimental realization has been reported so far. However, straightforward downsizing of an approach based on the circular Bragg reflection phenomenon has obvious inherent limitations.…”

“…17 and corresponding Focus Issue). Despite a few theoretical proposals to achieve photoinduced chiral separation [18][19][20][21][22][23] , the realization of an optical chiral sorter is, however, missing so far.…”

Helicity-dependent three-dimensional optical trapping of chiral microparticles

“…Although present results concern a given chiral material system explored at the 1-100 mm scale, combining this first experimental step to several recent theoretical studies on helicity-dependent optomechanics at the submicrometre scale [29][30][31][32] should motivate the development of practical realization of optomechanical strategies for selective optical trapping and manipulation of chiral objects whose application potential is multidisciplinary by nature.…”