Researchers from University of Bath observed optical activity in second-harmonic hyper-Rayleigh scattering
Chiral nano- or metamaterials and surfaces have useful photonic properties such as negative refractive index and superchiral light. Therefore, these properties find applications in novel optical components, nanorobotics, and allow enhanced chiral molecular interactions with light. Although nonlinear chiroptical techniques are more sensitive than their linear optical counterparts, separating true chirality from anisotropy is a major challenge. Now, a team of researchers at Department of Physics from the University of Bath used second-harmonic hyper-Rayleigh scattering (HRS) – the color-changing of light scattered from chiral molecules — to measure the chirality of molecules. According to the researchers, the technique is around 100,000 times more sensitive than currently used standard methods and can facilitate advancements in chemical manufacturing efficiency, miniaturization, and quality control in personalized pharmaceuticals.
In an experiment, the team dispersed nano-springs in water within a glass container where they spread randomly. The team later targeted the nano-springs with lasers and the circular polarization of the laser is switched periodically. The light scatters from the container at 90° and was analyzed to determine the chirality of the springs present. The team reported the first observation of optical activity in second-harmonic hyper-Rayleigh scattering (HRS) and demonstrated the effect in a 3D isotropic suspension of silver nanohelices in water. According to the researchers, the effect is 5 orders of magnitude stronger than linear optical activity. Moreover, HRS optical activity offers a fundamental breakthrough in chiral photonics for applications such as nanomaterials, metamaterials, and chemical molecules, owing to its sensitivity, isotropic environment, and straightforward experimental geometry.
Dr. Ventsislav Valev, who leads the research group in the Department of Physics at the University of Bath stated that highly sensitive test allows to use lower quantities in quality control and reduce waste in chemical and pharmaceutical manufacturing, along with microfluidics, in miniaturization and for developing personal pharmaceutical technologies. The team is focused on using the findings to characterize chiral molecules and to develop its technological applications. The findings were published in the journal Physical Review X on February 6, 2019.