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The advent of spatial control over the phase and amplitude of light waves has profoundly transformed photonics, enabling major advances in fields from imaging and information technology to biomedical optics. Here we propose a method of deterministic phase-front shaping using a planar thermo-optical module and designed microheaters to locally shape the refractive index distribution. When combined with a genetic algorithm optimization, this SmartLens can produce free-form optical wavefront modifications. Individually, or in arrays, it can generate complex functions based on either pure or combined Zernike polynomials, including lenses or aberration correctors of electrically tunable magnitude. This simple and compact concept complements the existing optical shaping toolbox by offering low-chromatic-aberration, polarization-insensitive and transmission-mode components that can readily be integrated into existing optical systems. Using microheaters and a genetic algorithm optimization, deterministic phase-front shaping through a planar thermo-optical module can be realized, complementing the existing optical shaping toolbox by offering low-chromatic-aberration, polarization-insensitive and transmission-mode components.

This Conference Presentation, “Dielectric nanophotonics for reconfigurable planar optics and biosensing,” was recorded for the Photonics West 2021 Digital Forum.

Fluorescence microscopy is the method of choice in biology for its molecular specificity and super-resolution capabilities. However, it is limited to a narrow z range around one observation plane. Here, we report an imaging approach that recovers the full electric field of fluorescent light with single-molecule sensitivity. We expand the principle of digital holography to fast fluorescent detection by eliminating the need for phase cycling and enable three-dimensional (3D) tracking of individual nanoparticles with an in-plane resolution of 15 nm and a z-range of 8 mm. As a proof-of-concept biological application, we image the 3D motion of extracellular vesicles (EVs) inside live cells. At short time scales (, Science Advances, 6 (45), ISSN:2375-2548

Integrating adjustable zoom lenses into mobile phones, miniaturized microscopes or medical endoscopes requires complex optics that can be reshaped electrically within milliseconds. We have recently demonstrated quasi-achromatic, polarization-insensitive electrical components that can apply predetermined, continuous local wavefront shaping with unprecedented degrees of freedom at the microscale, without mechanical movement.

Optical metasurfaces have shown to be a powerful approach to planar optical elements, enabling an unprecedented control over light phase and amplitude. At that stage, where a wide variety of static functionalities have been accomplished, most efforts are being directed toward achieving reconfigurable optical elements. Here, we present our approach to an electrically controlled varifocal metalens operating in the visible frequency range. It relies on dynamically controlling the refractive index environment of a silicon metalens by means of an electric resistor embedded into a thermo-optical polymer. We demonstrate precise and continuous tuneability of the focal length and achieve focal length variation larger than the Rayleigh length for voltage as small as 12 V. The system time-response is of the order of 100 ms, with the potential to be reduced with further integration. Finally, the imaging capability of our varifocal metalens is successfully validated in an optical microscopy setting. Compared to conventional bulky reconfigurable lenses, the presented technology is a lightweight and compact solution, offering new opportunities for miniaturized smart imaging devices.

By tailoring the anisotropy of light scattering along the surface of a macroscopic flat object, mechanical stabilization can be achieved without focused incident light or excessive constraints on the shape, size or material composition of the object.

The ability to manipulate light propagation at the nanoscale is of vital importance for future integrated photonic circuits. In this work we exploit the high contrast in the optical properties of the phase change material Ge2Sb2Te5 to control the propagation of surface plasmon polaritons at a Au/SiO2 interface. Using grating couplers, normally incident light at λ = 1.55 μm is converted into propagating surface plasmons on a Au waveguide. Single laser pulses (λ = 975 nm) are applied to a thin film of Ge2Sb2Te5 placed on top of the device, which, upon transition from its amorphous to crystalline structural phase, dramatically increases both its refractive index and absorption coefficient, thus inhibiting propagation of the plasmonic mode. This effect is investigated for different interaction lengths between the phase change material and the Au waveguide, and contrast values in the transmitted intensity up to several tens of percents are demonstrated.

In the current trend toward miniaturization, integrated micro-optical elements play a central role in the development of various applications including high-density data storage and imaging. In these operations, fine alignment and focus adjustment are usually performed mechanically, thus, limiting the accuracy, size and speed of devices. Here, we propose a novel reconfigurable microlens based on the engineering of the temperature distribution induced by a patterned plasmonic surface shined with a resonant near-infrared light. The refractive index change generated in a surrounding thermo-optical material acts as an effective lens whose parameters are remotely adjusted by the control near-infrared light. We demonstrate focal distance tunability of tens of microns with subnanometer accuracy along with time-responses down to 200 μs. The applicability of this photothermal lens is proved in the framework of optical microscopy and adaptive optics.

We introduce a deterministic procedure, named TSUNA for Temperature Shaping Using Nanoparticle Assemblies, aimed at generating arbitrary temperature distributions on the microscale. The strategy consists in (i) using an inversion algorithm to determine the exact heat source density necessary to create a desired temperature distribution and (ii) reproducing experimentally this calculated heat source density using smart assemblies of lithographic metal nanoparticles under illumination at their plasmonic resonance wavelength. The feasibility of this approach was demonstrated experimentally by thermal microscopy based on wavefront sensing., Nanoscale, 6 (15), ISSN:2040-3364, ISSN:2040-3372

International audience; The temperature distribution throughout arrays of illuminated metal nanoparticles is investigated numerically and experimentally. The two cases of continuous and fs-pulsed illumination are addressed. In the case of continuous illumination, two distinct regimes are evidenced: a temperature confinement regime - where the temperature increase remains confined at the vicinity of each nanosource of heat - and a temperature delocalization regime - where the temperature is uniform throughout the whole nanoparticle assembly despite of their nanometric size. We show that the occurrence of one regime or another simply depends on the geometry of the nanoparticle distribution. In particular, we derived simple expressions of i) dimensionless parameters aimed at predicting the degree of temperature confinement and ii) analytical expressions aimed at estimating the actual temperature increase at the centre of an assembly of nanoparticles under illumination, preventing heavy numerical simulations. All these theoretical results are supported by experimental measurements of the temperature distribution on regular arrays of gold nanoparticles under illumination. In the case of fs-pulsed illumination, we explain what are the two conditions that must be fulfilled to observe a further enhanced temperature spatial confinement.

Electron beam induced deposition (EBID) is used to grow on a transparent substrate plasmonic antennas formed by gold nanorods. We first discuss the influence of the growth parameters on the geometrical homogeneity of the structures. The optical response of optimized rods with different aspect ratios are measured using scattering spectroscopy. The optical data show antenna resonances in good agreement with 3D numerical simulations for pure gold antennas, validating EBID as a novel relevant technique for the fabrication of plasmonic nanostructures.

We introduce a numerical technique to investigate the temperature distribution in arbitrarily complex plasmonic systems subject to external illumination. We perform both electromagnetic and thermodynamic calculations based upon a time-efficient boundary element method. Two kinds of plasmonic systems are investigated in order to illustrate the potential of such a technique. First, we focus on individual particles with various morphologies. In analogy with electrostatics, we introduce the concept of thermal capacitance. This geometry-dependent quantity allows us to assess the temperature increase inside a plasmonic particle from the sole knowledge of its absorption cross section. We present universal thermal-capacitance curves for ellipsoids, rods, disks, and rings. Additionally, we investigate assemblies of nanoparticles in close proximity and show that, despite its diffusive nature, the temperature distribution can be made highly non-uniform even at the nanoscale using plasmonic systems. A significant degree of nanoscale control over the individual temperatures of neighboring particles is demonstrated, depending on the external light wavelength and direction of incidence. We illustrate this concept with simulations of gold sphere dimers and chains in water. Our work opens new possibilities for selectively controlling processes such as local melting for dynamic patterning of textured materials, chemical and metabolic thermal activation, and heat delivery for producing mechanical motion with spatial precision in the nanoscale. © 2010 American Chemical Society, This work has been supported by the Spanish MICINN (MAT2007-66050 and Consolider NanoLight.es) and by the EU (NMP4-SL-2008-213669-ENSEMBLE).

We investigate numerically the optical forces exerted by an incident light beam on metal nanoparticles (MNP) sustaining the so-called localized surface plasmons (LSP). We first describe how the particle dispersion can be used to tune the respective contribution from extinction and gradient forces. By a suitable adjustment of the illumination conditions, single MNP can be selectively guided, sorted and trapped. The second part of our work investigates the interparticle forces existing within a MNP ensemble. Our results show that MNP located in a conventional optical trap can self-arrange under optical forces according to specific architectures. In particular, at very low distances, they tend to agglomerate into metal clusters leading to very high field concentration in the interstices.

The implementation of optical tweezers1 at a surface opens a huge potential towards the elaboration of future lab-on-a-chip devices entirely operated with light2. The transition from conventional three-dimensional (3D) tweezers to 2D is made possible by exploiting evanescent fields bound at interfaces3,4,5. In particular, surface plasmons (SP) at metal/dielectric interfaces are expected to be excellent candidates to relax the requirements on incident power and to achieve subwavelength trapping volumes6,7. Here, we report on novel 2D SP-based optical tweezers formed by finite gold areas fabricated at a glass surface. We demonstrate that SP enable stable trapping of single dielectric beads under non-focused illumination with considerably reduced laser intensity compared with conventional optical tweezers. We show that the method can be extended to parallel trapping over any predefined pattern. Finally, we demonstrate how SP tweezers can be designed to selectively trap one type of particles out of a mixture, acting as an efficient optical sieve.

The momentum transfer between a photon and an object defines a fundamental limit for the precision with which the object can be measured. If the object oscillates at a frequency $\Omega_0$, this measurement back-action adds quanta $\hbar\Omega_0$ to the oscillator's energy at a rate $\Gamma_{\rm recoil}$, a process called photon recoil heating, and sets bounds to quantum coherence times in cavity optomechanical systems. Here, we use an optically levitated nanoparticle in ultrahigh vacuum to directly measure $\Gamma_{\rm recoil}$. By means of a phase-sensitive feedback scheme, we cool the harmonic motion of the nanoparticle from ambient to micro-Kelvin temperatures and measure its reheating rate under the influence of the radiation field. The recoil heating rate is measured for different particle sizes and for different excitation powers, without the need for cavity optics or cryogenic environments. The measurements are in quantitative agreement with theoretical predictions and provide valuable guidance for the realization of quantum ground-state cooling protocols and the measurement of ultrasmall forces

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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 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.

We investigate the physics of photoinduced heat generation in plasmonic structures by using a novel thermal microscopy technique based on molecular fluorescence polarization anisotropy. This technique enables us to image the heat source distribution in light-absorbing systems such as plasmonic nanostructures. While the temperature distribution in plasmonic nanostructures is always fairly uniform because of the fast thermal diffusion in metals, we show that the heat source density is much more contrasted. Unexpectedly the heat origin (thermal hot spots) usually does not correspond to the optical hot spots of the plasmon mode. Numerical simulations based on the Green dyadic method confirm our observations and enable us to derive the general physical rules governing heat generation in plasmonic structures.

One of the key challenges in current research into electromagnetic cloaking is to achieve invisibility at optical frequencies and over an extended bandwidth. There has been significant progress towards this using the idea of cloaking by sweeping under the carpet of Li and Pendry. Here, we show that we can harness surface plasmon polaritons at a metal surface structured with a dielectric material to obtain a unique control of their propagation. We exploit this control to demonstrate both theoretically and experimentally cloaking over an unprecedented bandwidth (650-900 nm). Our non-resonant plasmonic metamaterial is designed using transformational optics extended to plasmonics and allows a curved reflector to mimic a flat mirror. Our theoretical predictions are validated by experiments mapping the surface light intensity at a wavelength of 800 nm.

We present fiber-coupled dielectric-loaded plasmonic waveguides for 1.55 m telecom wavelength fabricated by two-photon polymerization and nanoimprint lithography. The waveguide structures include 100- m-long plasmonic waveguides connected on both ends to tapered dielectric waveguides used for end-fire coupling with optical fibers. The excitation of plasmonic waveguides is verified via polarization-resolved measurements of the overall transmission, demonstrating thereby that this technology is suitable in principle for the integration of plasmonic components into fiberoptics. Loss mechanisms are investigated and improvements suggested to reduce transmission losses and consequently increase the viability of practical application.

We report on a particularly strong third-order nonlinear response from nanostructured gold surfaces. Two incident laser beams with frequencies omega{1} and omega{2} give rise to four-wave mixing (4WM) fields with frequencies 2omega{1}-omega{2} and 2omega{2}-omega{1}. We demonstrate that the nonlinear response can be purely evanescent and that nanostructured surfaces convert the evanescent energy into propagating radiation, thereby increasing the efficiency of frequency conversion. The emitted 4WM radiation is found to be directional, polarized, coherent, and both frequency and angle tunable. The ability to perform efficient frequency conversion in reduced dimensions provides new opportunities for nanophotonics and active plasmonics.

We report on a novel approach, based on sub-wavelength spatial phase variations at the focus of high-order beams, to reconfigure the optical near field distribution near plasmonic nanostructures. We first show how the introduction of phase jumps in the incident field driving a gap nanoantenna strongly affects its near field response. Beyond, we demonstrate the feasibility of exploiting this approach to selectively switch on and off hot-spots sites within a complex antenna architecture.

A self–consistent model based on the classical field-susceptibilities formalism has been developed to simulate recent experiments where metallic particle chain waveguides are addressed locally by the tip of a Scanning Near-Field Optical Microscope (SNOM) [1]. This approach which accounts for the actual optical response of the particles leads to a reliable description of both near–field transmittances and losses of this kind of integrated devices.

We report on a thermal imaging technique based on fluorescence polarization anisotropy measurements, which enables mapping the local temperature near nanometer-sized heat sources with 300 nm spatial resolution and a typical accuracy of 0.1 degrees C. The principle is demonstrated by mapping the temperature landscape around plasmonic nano-structures heated by near-infrared light. By assessing directly the molecules' Brownian dynamics, it is shown that fluorescence polarization anisotropy is a robust and reliable method which overcomes the limitations of previous thermal imaging techniques. It opens new perspectives in medicine, nanoelectronics and nanofluidics where a control of temperature of a few degrees at the nanoscale is required.

Using optical tweezers combined with luminescence measurements we detected the optical field around two optically trapped silica microspheres partially covered by metal. By monitoring the luminescence of rhodamine 6G we were able to observe an increase of the local field intensity owing to the coupling of the local surface plasmons at the surfaces of two spheres.

We present spatially resolved spectral mode mapping of resonant plasmon gap antennas using two-photon luminescence microspectroscopy. The obtained maps are in good agreement with 3D calculations of the antenna modes. The evolution of the modal field with wavelength, both in the gap and along the two coupled gold nanowires forming the antenna, is directly visualized. At resonance, the luminescence for the gap area is enhanced at least 80 times and a comparison with the antenna extremities shows a dynamical charge redistribution due to the near-field coupling between the two arms.

Two-photon induced photoluminescence (TPL) microscopy has been used to probe the local field of nanoantennas. We demonstrate that TPL imaging is directly correlated to the antenna electromagnetic mode computed with a full 3D solver. Furthermore, spectroscopic mode mapping while scanning the incident wavelength enables near-field spectroscopy of specific areas of the antenna response, providing a deeper insight into its resonant properties.