Chirality is the property that the structure cannot be superimposed on its mirror image. Chiral materials have the property that they react differently to left-hand and right-hand circularly polarized light (optical activity). When a matter is irradiated with strong laser light, optical force acts on it. Theoretically, it was expected that the optical force exerted on chiral materials by left- and right-hand circularly polarized light would also be different.
The research group at the Institute for Molecular Science and three other universities used an experimental technique optical trapping to observe the circular polarization dependent optical gradient force exerted on chiral gold nanoparticles. Chiral gold nanoparticles have either a D-shape (right-handed) or an L-shape (left-handed) structure, and the experiment was performed with both. Although the gradient optical force acting on chiral nanoparticles has been theoretically predicted, no observation of the force has been reported so far. The research group succeeded in observing the optical gradient force originating from chirality (ie the difference between the gradient force due to left and right circularly polarized light) by optically trapping the chiral gold nanoparticles. The results showed that the gradient optical power was different for D-shape and L-shape particles. From the dependence of the force on the wavelength of the light used, they also found that there is a hitherto unknown effect on the mechanism of the chirality-dependent optical forces.
The present study elucidated the properties of the circular polarization dependent optical gradient force on the mechanics of chiral gold nanoparticles. It demonstrates the possibility of separating chiral materials by the optical force, which can be realized and broaden the applications by using localized light generated on nanostructures to trap the materials and/or by using the optical force used by other mechanisms.
– This press release was furnished by the National Institutes of Natural Sciences