Sculpting Light with Plasmon(2): Nanoemitter, Superchirality, and Discriminatory Optical Force

Sculpting light at nanoscale signifies a substantial step towards comprehensive manipulation of the interaction between photons and molecules. Since plasmon is nearly diffraction unlimited, light can be confined within nano-scale which makes the manipulation of scalar quantities such as wavelength, intensity, and phase easily be achieved. However, being capable of manipulating the polarization state at nanoscale at one’s desire is still challenging. This has been widely recognized as the last mile towards comprehensively control the interactions between photons and molecules, just like the famous remark made by Michael Faraday more than a hundred years ago: “Polarised light is the most subtle and delicate investigator of molecular condition.” Following the results obtained in the first year, in this 2-year-project, we plan to manipulate the polarization state and study the superchiral phenomenon at nanoscale, aiming at facilitating chirality recognition and enantiomer separation. The main methodologies employed in this project include: 1. The fabrication of plasmonic dimer, trimer, or oligomers; 2. Superresolved four wave mixing light generation; 3. Conical refraction based polarimetry; 4. Generalized multiparticle Mie (GMM) simulation; and 5. Waveguide based opto-fluidic technology. So far, preliminary results are obtained both theoretically and experimentally. We will then integrate functionality such as particle transportation by waveguide along with the nanoparticles to achieve chiral recognition and enantiomer separation simultaneously. Since the isolated nanostructure is much smaller than the laser spot (~1/10) and the shift of the absorption/scattering spectrum for molecules with opposite chirality is very small (~10 nm), we request a motor stage and a cryostat to improve the power stability and mitigate deadly thermal drift. It is hoped that with the requested instruments, the resolution and sensitivity can be largely improved. Besides, we will develop a brand-new algorithm based on the conversion between the measured spectrum and CIE 1931 color coordinates. The guidelines about synthesizing the optimal light source to maximize the coordinate shift for oppositely handed enantiomers will be yielded. This will enable one to distinguish chirality directly on the map. If the abovementioned targets are successfully achieved, the results will benefit to the scientific society and industry, in particular for the application in the field of bio-labeling, drug/toxicant identification, food safety, and environment monitoring.