Search

Efficient light-matter interaction lies at the heart of many emerging technologies that seek on-chip integration of solid-state photonic systems. Plasmonic waveguides, which guide the radiation in the form of strongly confined surface plasmon-polariton modes, represent a promising solution to manipulate single photons in coplanar architectures with unprecedented small footprints. Here we demonstrate coupling of the emission from a single quantum emitter to the channel plasmon polaritons supported by a V-groove plasmonic waveguide. Extensive theoretical simulations enable us to determine the position and orientation of the quantum emitter for optimum coupling. Concomitantly with these predictions, we demonstrate experimentally that 42% of a single nitrogen vacancy centre emission efficiently couples into the supported modes of the V-groove. This work paves the way towards practical realization of efficient and long distance transfer of energy for integrated solid-state quantum systems., 20 pages, 4 figures

We report on two-photon photoluminescence (TPL) spectroscopy on metal dimers made of two gold nanoparticles separated by subwavelength distances. A direct comparison with far-field scattering measure- ments shows that TPL provides additional data on the structure modes of major importance for their use in surface-enhanced Raman scattering, enhanced fluores- cence, and sensing.

In this paper we study the properties of microring resonator structures fabricated with high-index-of-refraction dielectric material. These structures concentrate light and can produce very strong optical potential gradients. They are of great interest for the trapping, manipulation and transport of cold atoms near surfaces. The study consists of two parts: in the first part we investigate the symmetry properties of the resonator response for simple models of the microring structures. In the second part we present detailed numerical calculations of the actual spectra for realistic microfabricated structures. We employ the direct space integral equation method (DSIEM). This method, based on a volume integral solving procedure, has already been found to cope successfully with nonresonant dielectric nanostructures. Such ab initio investigations of the optical near-field distributions only require a specification of the frequency-dependent dielectric constant and the precise shape of the fabricated structures. Consequently, these calculations can stand alone, or complement and inform anticipated experimental studies.

This letter reports near-field optical observations of light energy transport along micro-waveguides decorated by short chains of gold "nanodots". In spite of their subwavelength dimensions (100 nm diameter ×20 nm height), the metallic dots in the chain function as an efficient photonic band filter or a nanometric Bragg mirror. Numerical simulations reproduce the observed phenomenon and indicate that the occurrence of a band gap for light transport through the decorated guide corresponds to a selective absorption by the metallic chain.

Recent progress in near-field optics instrumentation led to a new class of subwavelength optical experiments in which it is intended to use either the optical tunnel effect (OTE) or the lower mode based transmission (LMBT) in order to control the optical transfer between several delocalized detection or injection centers. This paper presents a panel of new theoretical and experimental results computed or observed near various dielectric or metallic patterns, linear, curved, or dashed, integrated in coplanar geometry. In particular, we demonstrate, how an efficient control of light evanescent waves can allow structures of subwavelength cross sections to be addressed.

International audience

Noble metal nanoparticles supporting plasmonic resonances behave as efficient nanosources of light, heat and energetic electrons. Owing to these properties, they offer a unique playground to trigger chemical reactions on the nanoscale. In this tutorial review, we discuss how nanoplasmonics can benefit chemistry and review the most recent developments in this new and fast growing field of research.

We study the dynamics of a laser-trapped nanoparticle in high vacuum. Using parametric coupling to an external excitation source, the linewidth of the nanoparticle's oscillation can be reduced by three orders of magnitude. We show that the oscillation of the nanoparticle and the excitation source are synchronized, exhibiting a well-defined phase relationship. Furthermore, the external source can be used to controllably drive the nanoparticle into the nonlinear regime, thereby generating strong coupling between the different translational modes of the nanoparticle. Our work contributes to the understanding of the nonlinear dynamics of levitated nanoparticles in high vacuum and paves the way for studies of pattern formation, chaos, and stochastic resonance., 5 pages, 3 figures

Recent advances in nanotechnologies have prompted the need for tools to accurately and non-invasively manipulate individual nano-objects. Among the possible strategies, optical forces have been predicted to provide researchers with nano-optical tweezers capable of trapping a specimen and moving it in three dimensions. In practice, however, the combination of weak optical forces and photothermal issues has thus far prevented their experimental realization. Here, we demonstrate the first three-dimensional optical manipulation of single 50 nm dielectric objects with near-field nanotweezers. The nano-optical trap is built by engineering a bowtie plasmonic aperture at the extremity of a tapered metal-coated optical fibre. Both the trapping operation and monitoring are performed through the optical fibre, making these nanotweezers totally autonomous and free of bulky optical elements. The achieved trapping performances allow for the trapped specimen to be moved over tens of micrometres over a period of several minutes with very low in-trap intensities. This non-invasive approach is foreseen to open new horizons in nanosciences by offering an unprecedented level of control of nanosized objects, including heat-sensitive biospecimens.

Nanopositioning of single quantum emitters to control their coupling to integrated photonic structures is a crucial step in the fabrication of solid-state quantum optics devices. We use the optical near-field enhancement produced by nanofabricated gold antennas subject to near-infrared illumination to deterministically trap and position single nanodiamonds (NDs) hosting nitrogen-vacancy (NV) centers. The positioning of the NDs at the antenna regions of maximum field intensity is first characterized using both fluorescence and electron microscopy imaging. We further study the interaction between the nanoantenna and the delivered NV center by analyzing its change in fluorescence lifetime, which is driven by the increase in the local density of optical states at the trapping positions. Additionally, the plasmonic enhancement of the near-field intensity allows us to optically control the NV excited lifetime using relatively low NIR illumination intensities, some 20 times lower than in the absence of the antennas. ISSN:1530-6984 ISSN:1530-6992

International audience

International audience; Noble metal nanoparticles supporting plasmonic resonances behave as efficient nanosources of light, heat and energetic electrons. Owing to these properties, they offer a unique playground to trigger chemical reactions on the nanoscale. In this tutorial review, we discuss how nanoplasmonics can benefit chemistry and review the most recent developments along this new and fast growing field of research.

In this chapter, we give a comprehensive introduction to the emerging field of transformational plasmonics. We first review the basics of transformational optics, whereby changes of coordinates in Maxwell’s equations lead to the design of novel types of anisotropic heterogeneous media known as metamaterials. Electromagnetic paradigms such as invisibility cloak and carpet are used in order to exemplify the usefulness of this renewed approach to classical optics. We then apply tools of transformational optics to plasmonics. The idea is to control the surface plasmon polariton (SPP) wave trajectories by making changes of coordinates at the interface between a metal and a transformed medium. A number of illustrative examples including a concentrator, an SPP beam shifter, but also a broadband structured plasmonic carpet (demonstrated experimentally for wavelengths ranging from 750 to 900 nm at ICFO in 2010) and a multilayered plasmonic cloak, are given.

Fluctuation theorems are a generalization of thermodynamics on small scales and provide the tools to characterize the fluctuations of thermodynamic quantities in non-equilibrium nanoscale systems. They are particularly important for understanding irreversibility and the second law in fundamental chemical and biological processes that are actively driven, thus operating far from thermal equilibrium. Here, we apply the framework of fluctuation theorems to investigate the important case of a system relaxing from a non-equilibrium state towards equilibrium. Using a vacuum-trapped nanoparticle, we demonstrate experimentally the validity of a fluctuation theorem for the relative entropy change occurring during relaxation from a non-equilibrium steady state. The platform established here allows non-equilibrium fluctuation theorems to be studied experimentally for arbitrary steady states and can be extended to investigate quantum fluctuation theorems as well as systems that do not obey detailed balance., Comment: 5 figures

We report on the observation, in direct space, of both light localization and confinement effects near lithographically designed structures. The sample is observed in the optical near-field zone with a Photon Scanning Tunneling Microscope (PSTM). Several patterns composed of a few periods of TiO2 dots, arranged as a hexagonal lattice, have been investigated. When the central dot of the pattern is removed, a phenomenon of light localization above the vacancy can be observed in the PSTM image. The occurrence of this phenomenon can be related to the variation of the electromagnetic local density of state.

The intensity of optically-pumped fluorescence generated from a single atomic defect in diamond can be reduced by 80% in just 100 ns by applying infrared laser light. This result demonstrates the possibility of using these so-called nitrogen–vacancy centres to create optical switches that operate at room temperature.

Fully exploiting the capability of nano-optics to enhance light-matter interaction on the nanoscale is conditioned by bringing the nano-object to interrogate within the minuscule volume where the field is concentrated. There currently exists several approaches to control the immobilization of nano-objects but they all involve a cumbersome delivery step and require prior knowledge of the "hot spot" location. Herein, we present a novel technique in which the enhanced local field in the hot spot is the driving mechanism that triggers the binding of proteins via three-photon absorption. This way, we demonstrate exclusive immobilization of nanoscale amounts of bovine serum albumin molecules into the nanometer-sized gap of plasmonic dimers. The immobilized proteins can then act as a scaffold to subsequently attach an additional nanoscale object such as a molecule or a nanocrystal. This universal technique is envisioned to benefit a wide range of nano-optical functionalities including biosensing, enhanced spectroscopy like surface-enhanced Raman spectroscopy or surface-enhanced infrared absorption spectroscopy, as well as quantum optics.

Multipolar transitions other than electric dipoles are generally too weak to be observed at optical frequencies in single quantum emitters. For example, fluorescent molecules and quantum dots have dimensions much smaller than the wavelength of light and therefore emit predominantly as electric dipoles. Here we demonstrate controlled emission of a quantum dot into multipolar radiation through selective coupling to a linear nanowire antenna. The antenna resonance tailors the interaction of the quantum dot with light, effectively creating a hybrid nanoscale source beyond the simple Hertz dipole. Our findings establish a basis for the controlled driving of fundamental modes in nanoantennas and metamaterials, for the understanding of the coupling of quantum emitters to nanophotonic devices such as waveguides and nanolasers, and for the development of innovative quantum nano-optics components with properties not found in nature., Nature Communications, 4, ISSN:2041-1723

International audience

5 pags, 4 figs. -- Supplementary information is available in the online version of the paper., Nitrogen vacancy (NV) centres in diamond are promising elemental blocks for quantum optics, spin-based quantum information processing and high-resolution sensing. However, fully exploiting the capabilities of these NV centres requires suitable strategies to accurately manipulate them. Here, we use optical tweezers as a tool to achieve deterministic trapping and three-dimensional spatial manipulation of individual nanodiamonds hosting a single NV spin. Remarkably, we find that the NV axis is nearly fixed inside the trap and can be controlled in situ by adjusting the polarization of the trapping light. By combining this unique spatial and angular control with coherent manipulation of the NV spin and fluorescence lifetime measurements near an integrated photonic system, we demonstrate individual optically trapped NV centres as a novel route for both three-dimensional vectorial magnetometry and sensing of the local density of optical states. © 2013 Macmillan Publishers Limited. All rights reserved., This work was partially supported by the Spanish Ministry of Sciences (grants FIS2010–14834 and CSD2007–046-NanoLight.es), the European Community’s Seventh Framework Program under grant ERC-Plasmolight (no. 259196) and Fundacio ́ privada CELLEX.

Nano- and micromechanical oscillators with high quality (Q) factors have gained much attention for their potential application as ultrasensitive detectors. In contrast to micro-fabricated devices, optically trapped nanoparticles in vacuum do not suffer from clamping losses, hence leading to much larger Q-factors. We find that for a levitated nanoparticle the thermal energy suffices to drive the motion of the nanoparticle into the nonlinear regime. First, we experimentally measure and fully characterize the frequency fluctuations originating from thermal motion and nonlinearities. Second, we demonstrate that feedback cooling can be used to mitigate these fluctuations. The high level of control allows us to fully exploit the force sensing capabilities of the nanoresonator. Our approach offers a force sensitivity of 20 zN $Hz^{-1/2}$, which is the highest value reported to date at room temperature, sufficient to sense ultra-weak interactions, such as non-Newtonian gravity-like forces., Comment: 12 pages, 5 figures

In this chapter, we use analogies between the governing equations for linear surface liquid waves (LSWs) and surface plasmon polaritons (SPPs) in order to control their trajectories using geometric transforms. These two routes towards cloaking are emerging areas of physics known as transformational acoustics and plasmonics. We first analyze cloaking of LSWs propagating through a circular cloak, which consists of concentric layers cut into a large number of small sectors with rigid pillars. This water wave cloak behaves as an effective anisotropic fluid. We experimentally observe the decreased backscattering around the frequency 10 Hertz of a fluid with low viscosity and finite density (Methoxynonafluorobutane) from a cylindrical rigid obstacle surrounded by the cloak when it is located a couple of wavelengths away from the acoustic source. We then study theoretically, and numerically, the cloaking of SPPs propagating on a structured metal surface, and we manufacture and experimentally validate a plasmonic carpet working in the visible spectrum using dielectric plots of TiO2 arranged along a quasi-conformal grid on a metal plate.

International audience; The use of illuminated gold nanoparticles as ideal nanosources of heat is the basis of numerous research activities and applications in physics, chemistry, biology and medicine. This field defines the area recently named Thermoplasmonics [1]. In most of the activities related to Thermoplasmonics, probing the temperature at the vicinity of the metal nanoparticles is not an easy task. In this context, we recently developed a novel optical microscopy technique, named TIQSI, aimed at mapping the temperature around plasmonic nanoparticles [2]. The approach is based on the measure of the thermal-induced variation of the refractive index surrounding the sources of heat. The TIQSI technique cumulates all the advantages a thermal microscopy technique may require: i) high resolution (diffraction limited), ii) high readout rate (less than one image per second), iii) high temperature sensitivity (

We present the first evidence of nitrogen vacancy (NV) photoluminescence from a nanodiamond suspended in a free-space optical dipole trap at atmospheric pressure. The photoluminescence rates are shown to decrease with increasing trap laser power, but are inconsistent with a thermal quenching process. For a continuous-wave trap, the neutral charge state (NV$^0$) appears to be suppressed. Chopping the trap laser yields higher total count rates and results in a mixture of both NV$^0$ and the negative charge state (NV$^-$)., Comment: Updated to published version appearing in Optics Letters

We present nitrogen vacancy photoluminescence measurements from a nanodiamond levitated in a free-space optical-dipole trap. Photoluminescence decreases as trap laser power increases, and modulating the trap laser results in changes in the defect charge state.

We present the use of green fluorescent protein as a thermal nanoprobe suited for intracellular temperature mapping. In vivo and in vitro experiments show a spatial resolution of 300 nm and temperature accuracy of 0.4 C.

We first review basic equations of plasmonics in anisotropic media. We recall the origin of Maxwell’s gradient index fisheye lens. We then apply tools of transformation optics to the design of a cyclic concentrator and a variety of plasmonic carpet-cloaks. We further give a brief account of the discovery of spoof plasmon polaritons (SfPPs) by Pendry et al (2004 Science 305 847–8) 150 years after Maxwell invented the fisheye lens. Finally, we experimentally demonstrate a concept of a fisheye lens for SfPPs at microwave frequencies. We stress that perfect metal surfaces perforated with dielectrics offer a playground for moulding surface waves in many areas of physics

We study high-order harmonic generation (HHG) resulting from the illumination of plasmonic nanostructures with a short laser pulse of long wavelength. We demonstrate that both the confinement of the electron motion and the inhomogeneous character of the laser electric field play an important role in the HHG process and lead to a significant increase of the harmonic cutoff. In particular, in bow-tie nanostructures with small gaps, electron trajectories with large excursion amplitudes experience significant confinement and their contribution is essentially suppressed. In order to understand and characterize this feature, we combine the numerical solution of the time-dependent Schrodinger equation (TDSE) with the electric fields obtained from 3D finite element simulations. We employ time-frequency analysis to extract more detailed information from the TDSE results and classical tools to explain the extended harmonic spectra. The spatial inhomogeneity of the laser electric field modifies substantially the electron trajectories and contributes also to cutoff increase.

International audience; We report on an optical microscopy technique aimed at measuring the absolute absorption cross section of individual nanoparticles. It relies on the thermally induced variation of the refractive index of the surrounding medium subsequent to light absorption by the nanoparticle. The technique is illustrated on gold nanoparticles featuring a well-defined plasmonic resonance. Different plasmonic modes were evidenced and quantified. The simplicity and rapidity of the measurements make it possible to investigate absorption resonances of absorbing nanostructures and microstructures in a reasonable time frame. Furthermore, the experimental approach is simply based on the use of a wavefront analyzer, which is straightforward to implement on any conventional microscope.

This book deals with all aspects of plasmonics, basics, applications and advanced developments. Plasmonics is an emerging field of research dedicated to the resonant interaction of light with metals. The light/matter interaction is strongly enhanced at a nanometer scale which sparks a keen interest of a wide scientific community and offers promising applications in pharmacology, solar energy, nanocircuitry or also light sources. The major breakthroughs of this field of research originate from the recent advances in nanotechnology, imaging and numerical modelling. The book is divided into three main parts: extended surface plasmons polaritons propagating on metallic surfaces, surface plasmons localized on metallic particles, imaging and nanofabrication techniques. The reader will find in the book: Principles and recent advances of plasmonics, a complete description of the physics of surface plasmons, a historical survey with emphasize on the emblematic topic of Wood's anomaly, an overview of modern applications of molecular plasmonics and an extensive description of imaging and fabrications techniques.

We introduce and experimentally demonstrate the concept of multifrequency optical antennas that are designed for controlling the nonlinear response of materials. These antennas consist of two arms of different lengths, each resonant with one of the incoming frequencies. They are embedded in a nonlinear medium (indium tin oxide) that acts as a receiver. Because the two arms have different spectral resonances, tuning of the antenna gap size has minimal effect on the linear optical properties. However, it strongly affects the nonlinear response. Thus, by employing antenna elements with different spectral resonances, we provide a strategy to decouple the nonlinear response of nanomaterials from their linear optical properties.

We present theoretical studies of high-order harmonic generation (HHG) produced by non-homogeneous fields as resulting from the illumination of plasmonic nanostructures with a short laser pulse. We show that both the inhomogeneity of the local fields and the confinement of the electron movement play an important role in the HHG process and lead to the generation of even harmonics and a significantly increased cutoff, more pronounced for the longer wavelengths cases studied. In order to understand and characterize the new HHG features we employ two different approaches: the numerical solution of the time dependent Schr\"odinger equation (TDSE) and the semiclassical approach known as Strong Field Approximation (SFA). Both approaches predict comparable results and show the new features, but using the semiclassical arguments behind the SFA and time-frequency analysis tools, we are able to fully understand the reasons of the cutoff extension., Comment: 25 pages, 12 figures

Self-assembled Plasmonic Nanoparticle Networks (PNN) composed of chains of 12-nm diameter crystalline gold nanoparticles exhibit a longitudinally coupled plasmon mode cen- tered at 700 nm. We have exploited this longitudinal absorption band to efficiently confine light fields and concentrate heat sources in the close vicinity of these plasmonic chain net- works. The mapping of the two phenomena on the same superstructures was performed by combining two-photon luminescence (TPL) and fluorescence polarization anisotropy (FPA) imaging techniques. Besides the light and heat concentration, we show experimentally that the planar spatial distribution of optical field intensity can be simply modulated by controlling the linear polarization of the incident optical excitation. On the contrary, the heat production, which is obtained here by exciting the structures within the optically transparent window of biological tissues, is evenly spread over the entire PNN. This contrasts with the usual case of localized heating in continuous nanowires, thus opening opportunities for these networks in light-induced hyperthermia applications. Furthermore, we propose a unified theoretical framework to account for both the non-linear optical and thermal near-fields around PNN. The associated numerical simulations, based on a Green s function formalism, are in excellent agreement with the experimental images. This formalism therefore provides a versatile tool for the accurate engineering of optical and thermodynamical properties of complex plasmonic colloidal architectures.

Nanoscale single-photon emitters behave generally as dipoles. Here, we demonstrate multipolar and unidirectional emission of a quantum dot by near-field coupling to optical nanowire and Yagi-Uda antennas, that determine its angular radiation pattern and polarization.

Light plays a growing role in health science especially with the recent developments of new optical techniques that enable imaging biological processes down to the molecular scale and monitor dynamically physiological mechanisms in patients. In parallel, recent groundbreaking advances in nanotechnologies have opened new perspectives in medicine, for instance in creating new therapies or designing novel compact and highly sensitive diagnostic platforms. In this chapter, the aim is to discuss recent research that sits at the convergence of photonics, nanotechnology, and health. This research is based on the extraordinary optical properties of metallic nanoparticles (MNP) supporting Localized Surface Plasmon (LSP) (see Chap. 4). We discuss how plasmonic MNP can be used as nano-sources of either light or heat for biological and medical applications.

To optimize the signal-to-noise ratio of optically trapped nano-particles in high vacuum, we implemented a heterodyne interferometer to monitor particle motion in a backscattering configuration. The signal relays to a feedback loop that cools the nano-particle to sub-Kelvin temperatures.

We present theoretical studies of above-threshold ionization (ATI) produced by spatially inhomogeneous fields. This kind of field appears as a result of the illumination of plasmonic nanostructures and metal nanoparticles with a short laser pulse. We use the time-dependent Schr\"odinger equation in reduced dimensions to understand and characterize the ATI features in these fields. It is demonstrated that the inhomogeneity of the enhanced plasmonic field plays an important role in the ATI process and it produces appreciable modifications to the energy-resolved photoelectron spectra. In fact, our numerical simulations reveal that high-energy electrons can be generated. Specifically, using a linear approximation for the spatial dependence of the enhanced plasmonic field and with a near-infrared laser with intensities in the mid ${10}^{14}$ W/cm${}^{2}$ range, we show it is possible to drive electrons with energies in the near-keV regime. Furthermore, we study how the carrier envelope phase influences the emission of ATI photoelectrons for few-cycle pulses. Our quantum mechanical calculations are supported by their classical counterparts.

The resonance change of plasmonic nanostructures to a small variation of the shallow refractive index as induced by the binding of molecules to the metal surface determines the sensitivity of plasmonic sensors. The magnitude of this change is strongly determined by a number of factors including dielectric constant of the metal at the working wavelength, refractive indices of analyte, and surroundings [J Phys Chem B 109:21556–21565, 2005], but also the spatial overlap between the region of local refractive index change and the plasmon mode. In this chapter we discuss how the plasmon modes of lithographically prepared plasmonic nanostructures can be accurately engineered to design bio-chemical sensors with improved sensitivities.

This chapter presents as a proof of concept the development of a nanosensor based on the localized surface plasmon resonance for the analysis of biomolecules. The method presented take advantage of the plasmon generated in the surrounding of gold nanoparticles (i.e., 100 nm) for the specific interaction between antigen and antibody. The procedure for the optimization of an assay for the determination of biomolecules consisted mainly of four steps. First, the immobilization of gold nanoparticles over the glass surface using the appropriate ratio, concentration and time-contact of amino-sylilating agent, and nonreactive sylilating agent. Next, the suitable concentration of coating antigen in order to obtain the maximum signal LSPR. Following this step, the interaction between antigen and antibody (specific antibody) is evaluated by measuring the signal LSPR. Finally, a calibration curve was obtained for the detection of a small organic molecule such as stanozolol using this nanobiosensor. As a proof of concept, the use of a model is performed that in this case is for the detection of an anabolic androgenic steroid, such as stanozolol which is banned for the European Commission (EC) as a growth promoter and for the World Anti-Doping Agency (WADA) as a doping agent. The nanosensor developed demonstrates its feasibility for screening purposes due to the limit of detection achieved (0.7 μg/L) is under the MRPL required for both organizations (10 μg/L). A protocol such as that presented here may be generally applied for the analysis of other pollutant such as pesticides or antibiotics, or for biomedical applications for the analysis of biomarkers using the LSPR principle using gold nanoparticles (i.e., 30-120 nm).

This chapter presents as a proof of concept the development of a nanosensor based on the localized surface plasmon resonance for the analysis of biomolecules. The method presented take advantage of the plasmon generated in the surrounding of gold nanoparticles (i.e., 100 nm) for the specific interaction between antigen and antibody. The procedure for the optimization of an assay for the determination of biomolecules consisted mainly of four steps. First, the immobilization of gold nanoparticles over the glass surface using the appropriate ratio, concentration and time-contact of amino-sylilating agent, and nonreactive sylilating agent. Next, the suitable concentration of coating antigen in order to obtain the maximum signal LSPR. Following this step, the interaction between antigen and antibody (specific antibody) is evaluated by measuring the signal LSPR. Finally, a calibration curve was obtained for the detection of a small organic molecule such as stanozolol using this nanobiosensor. As a proof of concept, the use of a model is performed that in this case is for the detection of an anabolic androgenic steroid, such as stanozolol which is banned for the European Commission (EC) as a growth promoter and for the World Anti-Doping Agency (WADA) as a doping agent. The nanosensor developed demonstrates its feasibility for screening purposes due to the limit of detection achieved (0.7 μg/L) is under the MRPL required for both organizations (10 μg/L). A protocol such as that presented here may be generally applied for the analysis of other pollutant such as pesticides or antibiotics, or for biomedical applications for the analysis of biomarkers using the LSPR principle using gold nanoparticles (i.e., 30-120 nm).

Dielectric-loaded plasmonic waveguide disk resonators (WDRs) operating at telecom wavelengths are fabricated and investigated. Disks resonators of various radii coupled to a straight waveguide are studied both numerically and experimentally. For each disk radius, the gap between the disk and the waveguide is varied from 0 to 300 nm. Performance of the fabricated WDRs is characterized in the wavelength range of 1500–1620 nm using near-field optical microscopy. Wavelength selectivity and efficiency of the WDRs are evaluated and are in good agreement with numerical results.

While metals benefit from a strong nonlinearity at optical frequencies, its practical exploitation is limited by the weak penetration of the electric field within the metal and the screening by the surface charges. It is shown here that this limitation can be bypassed by depositing a thin dielectric layer on the metal surface or, alternatively, using a thin metal film. This strategy enables us to enhance four-wave mixing in metals by up to four orders of magnitude.

We report on an integrated optical trapping platform operated by simple fiber coupling. The system consists of a dielectric channel optical waveguide decorated with an array of gold micro-pads. Through a suitable engineering of the waveguide mode, we achieve light coupling to the surface plasmon resonance of the gold pads that act as individual plasmonic traps. We demonstrate parallel trapping of both micrometer size polystyrene beads and yeast cells at predetermined locations on the chip with only 20 mW total incident laser power.

Conventional optical tweezers, formed at the diffraction-limited focus of a laser beam, have become a powerful and flexible tool for manipulating micrometre-sized objects. Extending optical trapping down to the nanometre scale would open unprecedented opportunities in many fields of science, where such nano-optical tweezers would allow the ultra-accurate positioning of single nano-objects. Among the possible strategies, the ability of metallic nanostructures to control light at the subwavelength scale can be exploited to engineer such nano-optical traps. This Review summarizes the recent advances in the emerging field of plasmon-based optical trapping and discusses the details of plasmon tweezers along with their potential applications to bioscience and quantum optics.

We present resonant dielectric structures exhibiting arbitrarily large optical field enhancement, only limited by fabrication imperfections. Three different arrangements are investigated, based upon dielectric waveguides, dielectric particle arrays, and a combination of these two structures. Experimental confirmation of enhancement in a waveguide resonator is achieved by measuring the luminescence of quantum dots dispersed in the hot optical region of the structure. The performance of these systems can be readily controlled by simply changing geometrical parameters, which allows obtaining remarkable values of the intensity enhancement approaching 105 relative to the incident intensity over large volumes under feasible experimental conditions. This opens new avenues for all-optical switching and biosensing. © 2010 American Chemical Society., The authors thank Mark Kreuzer for surface functionalization and QD deposition and Marta Castro for fluorescence imaging to check for the QD coverage. This work has been supported by the Spanish MICINN (MAT2007-66050 and Consolider NanoLight.es) and the European Commission (FP7-248909 “LIMA” and NMP4-SL- 2008-213669 “ENSEMBLE”). J.R. and R.Q. acknowledge support from la Fundacio´ Cellex Barcelona.

We extend the discrete dipole approximation (DDA) and the Green's dyadic tensor (GDT) methods---previously dedicated to all-optical simulations---to investigate the thermodynamics of illuminated plasmonic nanostructures. This extension is based on the use of the thermal Green's function and a original algorithm that we named Laplace matrix inversion. It allows for the computation of the steady-state temperature distribution throughout plasmonic systems. This hybrid photothermal numerical method is suited to investigate arbitrarily complex structures. It can take into account the presence of a dielectric planar substrate and is simple to implement in any DDA or GDT code. Using this numerical framework, different applications are discussed such as thermal collective effects in nanoparticles assembly, the influence of a substrate on the temperature distribution and the heat generation in a plasmonic nanoantenna. This numerical approach appears particularly suited for new applications in physics, chemistry, and biology such as plasmon-induced nanochemistry and catalysis, nanofluidics, photothermal cancer therapy, or phase-transition control at the nanoscale.

We propose a novel deterministic protocol, based on continuous light flows, that enables us to control the concentration of light in generic plasmonic nanostructures. Based on an exact inversion of the response tensor of the nanosystem, the so-called Deterministic Optical Inversion (DOPTI) protocol provides a physical solution for the incident field leading to a desired near field pattern, expressed in the form of a coherent superposition of high order beams. We demonstrate the high degree of control achieved on complex plasmonic architectures and quantify its efficiency and accuracy.

Directed Emission The atomlike features of quantum dots—the discrete energy levels and subsequent emission of light at discrete wavelengths—make them key building blocks in optoelectronic circuits and optical communication. However, the emitted light tends to be omnidirectional, which limits applications that require accurate transmission between sender and receiver. Curto et al. (p. 930 ; see the Perspective by Giessen and Lippitz ) have designed an optical antenna, a shrunk-down version of the Yagi-Uda design used in microwave and radio communication, and show that coupling the quantum dot to the antenna provides control over the direction of the emitted light.

The ability of gratings made of dielectric ridges placed on top of flat metal layers to open gaps in the dispersion relation of surface plasmon polaritons (SPPs) is studied, both experimentally and theoretically. The gap position can be approximately predicted by the same relation as for standard optical Bragg stacks. The properties of the gap as a function of the grating parameters is numerically analyzed by using the Fourier modal method, and the presence of the gap is experimentally confirmed by leakage radiation microscopy. We also explore the performance of these dielectric gratings as SPP Bragg mirrors. The results show very good reflecting properties of these mirrors for a propagating SPP whose wavelength is inside the gap.