Polarization is one of the basic properties of electromagnetic waves conveying valuable information in signal transmission and sensitive measurements. Conventional methods for advanced polarization control impose demanding requirements on material properties and attain only limited performance. We demonstrated ultrathin, broadband, and highly efficient metamaterial-based terahertz polarization converters that are capable of rotating a linear polarization state into its orthogonal one. On the basis of these results, we created metamaterial structures capable of realizing near-perfect anomalous refraction. Our work opens new opportunities for creating high-performance photonic devices and enables emergent metamaterial functionalities for applications in the technologically difficult terahertz-frequency regime.

Surface-enhanced Raman scattering (SERS) intensities for individual Au nanospheres, nanoshells, and nanosphere and nanoshell dimers coated with nonresonant molecules are measured, where the precise nanoscale geometry of each monomer and dimer is identified through in situ atomic force microscopy. The observed intensities correlate with the integrated quartic local electromagnetic field calculated for each specific nanostructure geometry. In this study, we find that suitably fabricated nanoshells can provide SERS enhancements comparable to nanosphere dimers.

Metallic nanoparticles influence the quantum yield and lifetime of adjacent fluorophores in a manner dependent on the properties of the nanostructure. Here we directly compare the fluorescence enhancement of the near-infrared fluorophore IR800 by Au nanoshells (NSs) and Au nanorods (NRs), where human serum albumin (HSA) serves as a spacer layer between the nanoparticle and the fluorophore. Our measurements reveal that the quantum yield of IR800 is enhanced from approximately 7% as an isolated fluorophore to 86% in a NSs-HSA-IR800 complex and 74% in a NRs-HSA-IR800 complex. This dramatic increase in fluorescence shows tremendous potential for contrast enhancement in fluorescence-based bioimaging.

Our understanding of how the geometry of metallic nanostructures controls the properties of their surface plasmons, based on plasmon hybridization, is useful for developing high-performance substrates for surface enhanced spectroscopies. In this tutorial review, we outline the design of metallic nanostructures tailored specifically for providing electromagnetic enhancements for surface enhanced Raman scattering (SERS). The concepts developed for nanoshell-based substrates can be generalized to other nanoparticle geometries and scaled to other spectroscopies, such as surface enhanced infrared absorption spectroscopy (SEIRA).