https://phys.org/news/2018-12-reactive-optical-light-induced-motion.html

The predicted nonreciprocal forces were demonstrated with simulations to vary very little with interparticle separation. However, straightforward experimental evidence on the phenomenon was not presented thus far. Exploring the reactive optical effects can open new possibilities of self-assembling, light-driven micromachines to herald a new field in optics and photonics.

To fill the experimental gap, in the present study, Yifat et al. demonstrated self-motility using optically bound dimers of disproportionate metallic nanoparticles (NPs). The experimental findings were also supported by quantitative electrodynamic simulations. Aside from dimers, the scientists similarly generated and measured the motion of asymmetric nanoparticle clusters or assemblies. To perform the experiments, Yifat et al. used a standard optical trapping setup with a Ti:Sapphire laser operating at a wavelength of 790 nm. A tightly focused, circularly polarized spatially phase-modulated beam of light formed an optical ring trap.