Light polarization research sees new light

Polarization response of a nanoparticle dimer.

Manipulating light on the nanometer scale is a challenging endeavor worldwide not only for the fundamental study, but also for applications aiming at the design of miniature optical devices. In recent years, the plasmonis becomes a rapidly emerging field of photonics that offers solutions to manipulate light by using surface plasmon excitations on metal nanostructures.
As we may learn, direction, intensity, spectrum and polarization are some primary properties of light. And through plasmonis, scientists managed to manipulate the first three properties on the nano-scale. While a less explored yet particularly important property of light to control is its polarization. Breakthroughs in the latter can largely renovate the study in the areas like the single molecule spectroscopy, supersensitive detection, integrated optic chips and quantum communication.
A research group headed by Prof. XU Hongxing with the Beijing National Lab of Condensed Matter Physics, CAS Institute of Physics, has been engaged in this study for years and recently succeeded in managing the polarization of the Raman-scattered (RS) light from a single molecule on the nanoscale. Their research paper entitled "Managing light polarization via plasmon molecule interactions within an asymmetric metal nanoparticle trimer" was published in a recent issue of the Proceedings of the National Academy of Sciences.
The scientists employed RS light from individual molecules to probe the response of asymmetric nanoparticle aggregates (which are asymmetric silver nanocrystal trimers they used in the experiment) over a range of wavelengths and to show that these aggregates can dramatically modulate the polarization of the emitted light.
The results showed that the RS light could be elliptically polarized because of strong plasmonic coupling between all the trimer nanoparticals and its intensity pattern was actually rotated. Then the scientists made further research to find that this coupling depends crucially on the wavelength of the light, the relative sizes of the nanoparticles and their relative distances.