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Plasmonic resonance of metallic nanoparticles results from coherent motion of its conduction electrons, driven by incident light. For the nanoparticles less than 10 nm in diameter, localized surface plasmonic resonances become sensitive to the quantum nature of the conduction electrons. Unfortunately, quantum mechanical simulations based on time-dependent Kohn–Sham density functional theory are computationally too expensive to tackle metal particles larger than 2 nm. Herein, we introduce the recently developed time-dependent orbital-free density functional theory (TD-OFDFT) approach which enables large-scale quantum mechanical simulations of plasmonic responses of metallic nanostructures. Using TD-OFDFT, we have performed quantum mechanical simulations to understand size-dependent plasmonic response of Na nanoparticles and plasmonic responses in Na nanoparticle dimers and trimers. An outlook of future development of the TD-OFDFT method is also presented.

Quantum plasmonics opens the option to integrate complex quantum optical circuitry onto chip scale devices. In the past, often external light sources were used and nonclassical light was coupled in and out of plasmonic structures, such as hole arrays or waveguide structures. Another option to launch single plasmonic excitations is the coupling of single emitters in the direct proximity of, e.g., a silver or gold nanostructure. Here, we present our attempts to integrate the research of single emitters with wet-chemically grown silver nanowires. The emitters of choice are single organic dye molecules under cryogenic conditions, which are known to act as high-brightness and extremely narrow-band single photon sources. Another advantage is their high optical nonlinearity, such that they might mediate photon–photon interactions on the nanoscale. We report on the coupling of a single molecule fluorescence emission through the wire over the length of several wavelengths. The transmission of coherently emitted photons is proven by an extinction type experiment. As for influencing the spectral properties of a single emitter, we are able to show a remote change of the line-width of a single terrylene molecule, which is in close proximity to the nanowire.

Spatial nonlocality in the photonic response of metallic nanoparticles is actually known to produce near-field quenching and significant plasmon frequency shifts relative to local descriptions. As the control over size and morphology of fabricated nanostructures is truly reaching the nanometer scale, understanding and accounting for nonlocal phenomena is becoming increasingly important. Recent advances clearly point out the need to go beyond the local theory. We here present a general formalism for incorporating spatial dispersion effects through the hydrodynamic model and generalizations for arbitrary surface morphologies. Our method relies on the boundary element method, which we supplement with a nonlocal interaction potential. We provide numerical examples in excellent agreement with the literature for individual and paired gold nanospheres, and critically examine the accuracy of our approach. The present method involves marginal extra computational cost relative to local descriptions and facilitates the simulation of spatial dispersion effects in the photonic response of complex nanoplasmonic structures.

The near-field distribution of surface plasmon polariton (SPP) on metallic photonic crystal slabs has been studied. Preliminary numerical simulations indicate that the interference of SPP on the exit side of metallic photonic crystal slabs can redistribute the illumination light into nano-scale spatial distribution, which beats the Rayleigh diffraction limit. The electric field distribution of SPP with a resolution of 50 nm was measured by recording the high intensity range into photoresist with a wavelength of 436 nm. Because of the small wavelength of the plasmon wave, a much higher spatial resolution can be obtained, which can provide a new nano-fabrication or nano-storage method by using optical light with a long wavelength.

The transmission properties of rectangular one-dimensional unperforated metallic periodic structures for frequencies close to the surface plasmon band are investigated experimentally and theoretically. The results reveal that it is possible to obtain unexpectedly large transmissions through thick unperforated metallic structures. The mechanisms of enhanced transmissions are attributed to resonant excitations of three kinds of plasmon radiations: coupled surface plasmon polaritons, horizontal localized groove plasmon mode, and vertical localized groove plasmons mode. Once the surface plasmon polaritons and the vertical groove plasmon modes are excited simultaneously, the transmission approaches to maximum at the coincident condition.

The spatial distribution of the interference of surface plasmon polariton (SPP) on metallic nanostructures has been studied. The results show that the transmission of electromagnetic radiation is remarkably enhanced for frequencies close to the surface plasmon band and the interference of SPP can redistribute the illumination light into subwavelength-scale spatial distribution with high intensity, which beats the Rayleigh diffraction limit. For an appropriate thickness, the transmission of an unperforated structure can be larger than that of holes or slits systems with the same periodicity and thickness when the coupled surface plasmon wave mode is excited. With the help of the interference of the horizontal plasmon excited by Bragg resonance due to the periodicity in the horizontal direction, the vertical plasmons, excited in z direction via Fabry–Perot cavity resonance in different grooves, are correlated, so the transmission is increased via the tunneling process. The properties of transparency for light but impenetrability for gas and liquid will be of importance for device applications. The information on near-field distribution from perforated metallic structures is important for understanding the underlying physics, as well as for optimizing photonic crystals for possible applications.

A mode separation approach in the nanoring resonator by a cascaded slot cavity is proposed and numerically investigated using the finite-difference time-domain (FDTD) method. With the cascaded slot cavity, the specified modes in the nanoring can be separated to realize a wide free spectral range (FSR) or single channel filtering, which provides a free degree to the plasmonic filters design. Simulation results also demonstrate that the full-width at half-maximum (FWHM) of the single channel filter obtained from the cascaded slot cavity can be effectively reduced to meet various requirements.

In this paper, a wide-angle polarization-sensitive dual-band absorber at infrared wavelengths with a multilayer grating is reported. The simulation results show that the absorber has two absorption peaks at wavelengths λ = 1.365 μm and λ = 3.035 μm with the absorption magnitudes more than 0.97 and 0.99 for TM polarization (electric field perpendicular to the strips), respectively. And this absorber reflects almost all TE polarization (electric field parallel to the strips) light. The dual-band absorption peaks can be tuned by varying the width of the strips, and the absorption magnitudes are more than 0.9 for the dual-band absorption peaks for angles up to 70°.

We report a multiband absorber with dielectric–dielectric–metal structure in the infrared regime. The simulation results show that that near-perfect absorption is originated from the guide mode resonance and surface plasmonic polaritons (SPPs) excitation. Furthermore, the absorption peaks of this multiband absorber can be tuned by changing the incidence angle or scaling the microstructure dimensions. The results of this study have possible future potential applications in thermal emitter and sensor.