Plasmonic Surface Lattice Resonances: A Review of Properties and Applications.

When metal nanoparticles are arranged in an ordered array, they may scatter light to produce diffracted waves. If one of the diffracted waves then propagates in the plane of the array, it may couple the localized plasmon resonances associated with individual nanoparticles together, leading to an exciting phenomenon, the drastic narrowing of plasmon resonances, down to 1-2 nm in spectral width. This presents a dramatic improvement compared to a typical single particle resonance line width of >80 nm. The very high quality factors of these diffractively coupled plasmon resonances, often referred to as plasmonic surface lattice resonances, and related effects have made this topic a very active and exciting field for fundamental research, and increasingly, these resonances have been investigated for their potential in the development of practical devices for communications, optoelectronics, photovoltaics, data storage, biosensing, and other applications. In the present review article, we describe the basic physical principles and properties of plasmonic surface lattice resonances: the width and quality of the resonances, singularities of the light phase, electric field enhancement, etc. We pay special attention to the conditions of their excitation in different experimental architectures by considering the following: in-plane and out-of-plane polarizations of the incident light, symmetric and asymmetric optical (refractive index) environments, the presence of substrate conductivity, and the presence of an active or magnetic medium. Finally, we review recent progress in applications of plasmonic surface lattice resonances in various fields.

Enhancing the magneto-optical Kerr effect through the use of a plasmonic antenna.

We employ an extended finite-element model as a design tool capable of incorporating the interaction between plasmonic antennas and magneto-optical effects, specifically the magneto-optical Kerr effect (MOKE). We first test our model in the absence of an antenna and show that for a semi-infinite thin-film, good agreement is obtained between our finite-element model and analytical calculations. The addition of a plasmonic antenna is shown to yield a wavelength dependent enhancement of the MOKE. The antenna geometry and its separation from the magnetic material are found to impact the strength of the observed MOKE signal, as well as the antenna's resonance wavelength. Through optimization of these parameters we achieved a MOKE enhancement of more than 100 when compared to a magnetic film alone. These initial results show that our modeling methodology offers a tool to guide the future fabrication of hybrid plasmonic magneto-optical devices and plasmonic antennas for magneto-optical sensing.

Strong coupling between surface plasmon polaritons and emitters: a review.

In this review we look at the concepts and state-of-the-art concerning the strong coupling of surface plasmon-polariton modes to states associated with quantum emitters such as excitons in J-aggregates, dye molecules and quantum dots. We explore the phenomenon of strong coupling with reference to a number of examples involving electromagnetic fields and matter. We then provide a concise description of the relevant background physics of surface plasmon polaritons. An extensive overview of the historical background and a detailed discussion of more recent relevant experimental advances concerning strong coupling between surface plasmon polaritons and quantum emitters is then presented. Three conceptual frameworks are then discussed and compared in depth: classical, semi-classical and fully quantum mechanical; these theoretical frameworks will have relevance to strong coupling beyond that involving surface plasmon polaritons. We conclude our review with a perspective on the future of this rapidly emerging field, one we are sure will grow to encompass more intriguing physics and will develop in scope to be of relevance to other areas of science.

Optical field-enhancement and subwavelength field-confinement using excitonic nanostructures.

We show that dye-doped polymers open an interesting route to controlling light at the nanoscale. Just as for the much better known metal-based plasmonic systems, propagating and localized modes are possible. We show that the attractive features offered by plasmonics, specifically enhanced optical fields and subwavelength field confinement, are also available with these materials. They thus open a new opportunity in nanophotonics in which fabrication and functionality might be achieved by harnessing molecular and supramolecular chemistry.

THz generation from plasmonic nanoparticle arrays.

We investigate the generation of THz pulses when arrays of silver nanoparticles are irradiated by femtosecond laser pulses, providing the first reproducible experimental evidence in support of recent theoretical predictions of such an effect. We assess our results in the context of a model where photoelectrons are produced by plasmon-mediated multiphoton excitation, and THz radiation is generated via the acceleration of the ejected electrons by ponderomotive forces arising from the inhomogeneous plasmon field. By exploring the dependence of the THz emission on the femtosecond pulse intensity and as a function of metal nanoparticle morphology, and by comparing measurements to numerical modeling, we are able to verify the role of the particle plasmon mode in this process.

Composite au nanostructures for fluorescence studies in visible light.

We present results from composite plasmonic nanostructures designed to achieve the cascaded enhancement of electromagnetic fields at optical frequencies. Our structures comprise a small metallic nanodisc suspended above a larger disk. We probe the optical properties of these structures by coating them with a layer of a visible-light fluorophore and observing fluorescence signals with the help of scanning confocal microscopy. A 43 +/- 5-fold increase in the far-field fluorescence signal has been observed for two-tier composite nanostructures, when compared to the signal obtained from individual nanodiscs. Our results offer the prospect of using such nanostructures for field concentration, optical manipulation of nanoobjects, chemical and biological sensing.

Cascaded optical field enhancement in composite plasmonic nanostructures.

We present composite plasmonic nanostructures designed to achieve cascaded enhancement of electromagnetic fields at optical frequencies. Our structures were made with the help of electron-beam lithography and comprise a set of metallic nanodisks placed one above another. The optical properties of reproducible arrays of these structures were studied by using scanning confocal Raman spectroscopy. We show that our composite nanostructures robustly demonstrate dramatic enhancement of the Raman signals when compared to those measured from constituent elements.

Double-grating-structured light microscopy using plasmonic nanoparticle arrays.

Structured illumination increases the spatial bandwidth of optical microscopes. We demonstrate bandwidth extension using a physical grating placed close to the sample. This comprises an array of elongated nanoparticles, whose localized surface plasmon resonance is polarization dependent. By arranging the particle orientation to vary with position the grating can be moved by changing the input polarization. A projected optical grating provides an additional independent mechanism for bandwidth extension. Experimental results showing bandwidth improvement in one direction are presented, and the measures necessary to extend the technique for routine imaging are discussed.

Energy transfer across a metal film mediated by surface plasmon polaritons.

Coupled surface plasmon polaritons (SPPs) are shown to provide effective transfer of excitation energy from donor molecules to acceptor molecules on opposite sides of metal films up to 120 nanometers thick. This variant of radiative transfer should allow directional control over the flow of excitation energy with the use of suitably designed metallic nanostructures, with SPPs mediating transfer over length scales of 10(-7) to 10(-4) meters. In the emerging field of nanophotonics, such a prospect could allow subwavelength-scale manipulation of light and provide an interface to the outside world.

Surface plasmon polaritons and their role in the enhanced transmission of light through periodic arrays of subwavelength holes in a metal film.

We present results of the transmitted, reflected, and absorbed power associated with the enhanced transmittance of light through a silver film pierced by a periodic array of subwavelength holes. Comparing experimentally acquired dispersion curves under different polarization conditions shows that the transmission features of the array are consistent with p-polarized resonant modes of the structure. By exploring the regime in which no propagating diffracted orders are allowed, we further show that the transmittance maxima are associated with both reflectance minima and absorption maxima. These new results provide strong experimental evidence for transmission based on diffraction, assisted by the enhanced fields associated with surface plasmon polaritons.

Förster energy transfer in an optical microcavity.

By studying the transfer of excitation energy between dye molecules confined within an optical microcavity, we demonstrate experimentally that Förster energy transfer is influenced by the local photonic mode density. Locating donor and acceptor molecules at well-defined positions allows the transfer rate to be determined as a function of both mutual separation and cavity length. The results show that the Förster transfer rate depends linearly on the donor emission rate and hence photonic mode density, providing the potential to control energy transfer by modification of the optical environment.

High-quantum-efficiency Er(3+) fiber lasers pumped at 980 nm.

Significant improvements in the operation of Er(3+)-doped silica fiber lasers operating at wavelengths between 1.5 and 1.6 microm are reported. The use of 980 nm as the pump wavelength provides an output that is limited mainly by the quantum efficiency of the lasing process. It is thus considerably more efficient than previous results using ~810-nm pumping, where excited-state absorption degrades the lasing performance. Operation at three discrete output wavelengths is observed and is accounted for by studying gain across the lasing bandwidth.

Calibration of a satellite infrared radiometer.

The calibration procedure is described for a two-channel imaging radiometer on board the Heat Capacity Mapping Mission, a single sensor satellite in a near polar orbit. The Heat Capacity Mapping Radiometer measures radiation temperature and reflectivity with an instantaneous FOV of 600 m and a noise equivalent temperature of 0.4 K at 280 K in the thermal IR channel. Unexplained changes in the system during satellite launch were treated through comparison with surface/atmosphere data to force agreement. This necessitated an offset from the prelaunch calibration by 5.5 K. Later comparisons showed no difference. Possible explanations are described.