Scheme 1. Schematic illustration of the physiochemical mechanisms and applications of chirality transfer from chiral molecules to plasmonic NPs.

We have devised a simple method to determine the absorption and radiative decay rates of surface plasmon polaritons in an Au nanohole array by combining polarization-resolved reflectivity spectroscopy and temporal coupled-mode theory. The dependence of two rates on wavelength has been measured and they are found to agree with finite-difference time-domain simulations. As both absorption and radiative decay rates play a key role in several plasmonic applications, our approach offers a simple and effective means in determining them.

Enhancing the circular dichroism signals of chiral plasmonic nanostructures is vital for realizing miniaturized functional chiroptical devices, such as ultrathin wave plates and high-performance chiral biosensors. Rationally assembling individual plasmonic metamolecules into coupled nanoclusters or periodic arrays provides an extra degree of freedom to effectively manipulate and leverage the intrinsic circular dichroism of the constituent structures. Here, we show that sophisticated manipulation over the geometric parameters of a plasmonic stereo-metamolecule array enables selective excitation of its surface lattice resonance mode either by left- or right-handed circularly polarized incidence through diffraction coupling, which can significantly amplify the differential absorption and hence the intrinsic circular dichroism. In particular, since the diffraction coupling requires no index-matching condition and its handedness can be switched by manipulating the refractive index of either the superstrate or the substrate, it is therefore possible to achieve dynamic tuning and active control of the intrinsic circular dichroism response without the need of modifying structure parameters. Our proposed system provides a versatile platform for ultrasensitive chiral plasmonics biosensing and light field manipulation.

We show the spectral figure-of-merit (FOM) from nanohole arrays can be larger than 1900/RIU by phase-based surface plasmon resonance. By using temporal coupled mode theory, we find the p-s polarization phase jump is the sharpest when both the absorption and radiative decay rates of surface plasmon polaritons are matched, yielding an extremely small spectral differential phase linewidth and thus superior FOM. The result is supported by numerical simulation and experiment. As a demonstration, we show the phase detection outperforms the conventional spectral counterpart significantly by sensing the binding of bovine serum albumin antibodies under identical condition.

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Plasmonic chiral nanostructures have attracted a great deal of attention in chirality-based biosensing, enantioselective separation, and recently photonic orbital angular momentum-based quantum information processing. However, the intrinsic Ohmic losses of metals and significant radiative scattering of plasmonically resonant nanostructures result in small quality factors and hence weak optical chirality (such as circular dichroism, CD). Here, it is reported that propagating surface plasmon polaritons (SPPs)-an achiral electromagnetic surface wave-can significantly enhance the Q-factors of localized surface plasmon resonance (LSPR) related CD in plasmonic lattices with chiral unit cells. It is demonstrated experimentally and theoretically that mode interaction between the highly dispersive achiral SPPs and the nondispersive chiral LSPR results in the formation of hybrid chiral SPPs, enabling efficient tuning of the resultant transmission CD dispersion and signal intensity. A maximum CD signal of 0.8 is experimentally observed with a Q-factor of 45 in the visible spectral region, showing good agreement with theoretical calculations. This study provides an effective yet facile approach for engineering both the strength and dispersion of optical chirality, paving the way for realizing large-scale, low-cost, and high-performing chiral plasmonic and dielectric metasurfaces for a variety of sensing, imaging, and information manipulation.

We studied the effects of absorption and radiative decay rates of surface plasmon polaritons on the field enhancement in periodic metallic arrays by temporal coupled mode theory and finite-difference time-domain simulation. When two rates are equal, the field enhancement is the strongest and the peak height of the orthogonal reflectivity reaches 0.25. To demonstrate this fact, we fabricated two series of two-dimensional Au and Ag nanohole arrays with different geometries and measured their corresponding reflectivity and decay rates. The experimental results agree well with the analytical and numerical results.

We have studied the dependence of the rotation angle and ellipticity on the sample orientation and incident polarization from metallic nanohole arrays. The arrays have four-fold symmetry and thus do not possess any intrinsic chirality. We elucidate the role of surface plasmon